





Network Working Group                                         J. Quittek
Request for Comments: 5190                                M. Stiemerling
Category: Standards Track                                            NEC
                                                            P. Srisuresh
                                                          Kazeon Systems
                                                              March 2008


       Definitions of Managed Objects for Middlebox Communication

Status of This Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Abstract

   This memo defines a portion of the Management Information Base (MIB)
   for use with network management protocols in the Internet community.
   In particular, it describes a set of managed objects that allow
   configuring middleboxes, such as firewalls and network address
   translators, in order to enable communication across these devices.
   The definitions of managed objects in this documents follow closely
   the MIDCOM semantics defined in RFC 5189.
























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Table of Contents

   1. Introduction ....................................................4
   2. The Internet-Standard Management Framework ......................4
   3. Overview ........................................................4
      3.1. Terminology ................................................5
   4. Realizing the MIDCOM Protocol with SNMP .........................6
      4.1. MIDCOM Sessions ............................................6
           4.1.1. Authentication and Authorization ....................6
      4.2. MIDCOM Transactions ........................................7
           4.2.1. Asynchronous Transactions ...........................7
           4.2.2. Configuration Transactions ..........................8
           4.2.3. Monitoring Transactions ............................11
           4.2.4. Atomicity of MIDCOM Transactions ...................12
                  4.2.4.1. Asynchronous MIDCOM Transactions ..........12
                  4.2.4.2. Session Establishment and
                           Termination Transactions ..................12
                  4.2.4.3. Monitoring Transactions ...................13
                  4.2.4.4. Lifetime Change Transactions ..............13
                  4.2.4.5. Transactions Establishing New
                           Policy Rules ..............................14
           4.2.5. Access Control .....................................14
      4.3. Access Control Policies ...................................14
   5. Structure of the MIB Module ....................................15
      5.1. Transaction Objects .......................................16
           5.1.1. midcomRuleTable ....................................17
           5.1.2. midcomGroupTable ...................................19
      5.2. Configuration Objects .....................................20
           5.2.1. Capabilities .......................................20
           5.2.2. midcomConfigFirewallTable ..........................21
      5.3. Monitoring Objects ........................................22
           5.3.1. midcomResourceTable ................................22
           5.3.2. midcomStatistics ...................................24
      5.4. Notifications .............................................25
   6. Recommendations for Configuration and Operation ................26
      6.1. Security Model Configuration ..............................26
      6.2. VACM Configuration ........................................27
      6.3. Notification Configuration ................................28
      6.4. Simultaneous Access .......................................28
      6.5. Avoiding Idempotency Problems .............................29
      6.6. Interface Indexing Problems ...............................29
      6.7. Applicability Restrictions ................................30
   7. Usage Examples for MIDCOM Transactions .........................30
      7.1. Session Establishment (SE) ................................31
      7.2. Session Termination (ST) ..................................31
      7.3. Policy Reserve Rule (PRR) .................................31
      7.4. Policy Enable Rule (PER) after PRR ........................33
      7.5. Policy Enable Rule (PER) without Previous PRR .............34



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      7.6. Policy Rule Lifetime Change (RLC) .........................35
      7.7. Policy Rule List (PRL) ....................................35
      7.8. Policy Rule Status (PRS) ..................................35
      7.9. Asynchronous Policy Rule Event (ARE) ......................36
      7.10. Group Lifetime Change (GLC) ..............................36
      7.11. Group List (GL) ..........................................36
      7.12. Group Status (GS) ........................................37
   8. Usage Examples for Monitoring Objects ..........................37
      8.1. Monitoring NAT Resources ..................................37
      8.2. Monitoring Firewall Resources .............................38
   9. Definitions ....................................................38
   10. Security Considerations .......................................85
      10.1. General Security Issues ..................................85
      10.2. Unauthorized Middlebox Configuration .....................86
      10.3. Unauthorized Access to Middlebox Configuration ...........87
      10.4. Unauthorized Access to MIDCOM Service Configuration ......88
   11. Acknowledgements ..............................................88
   12. IANA Considerations ...........................................88
   13. Normative References ..........................................88
   14. Informative References ........................................90































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1.  Introduction

   This memo defines a portion of the Management Information Base (MIB)
   for use with network management protocols in the Internet community.
   In particular, it describes a set of managed objects that allow
   controlling middleboxes.

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

2.  The Internet-Standard Management Framework

   For a detailed overview of the documents that describe the current
   Internet-Standard Management Framework, please refer to section 7 of
   RFC 3410 [RFC3410].

   Managed objects are accessed via a virtual information store, termed
   the Management Information Base or MIB.  MIB objects are generally
   accessed through the Simple Network Management Protocol (SNMP).
   Objects in the MIB are defined using the mechanisms defined in the
   Structure of Management Information (SMI).  This memo specifies a MIB
   module that is compliant to the SMIv2, which is described in STD 58,
   RFC 2578 [RFC2578], STD 58, RFC 2579 [RFC2579] and STD 58, RFC 2580
   [RFC2580].

3.  Overview

   The managed objects defined in this document serve for controlling
   firewalls and Network Address Translators (NATs).  As defined in
   [RFC3234], firewalls and NATs belong to the group of middleboxes.  A
   middlebox is a device on the datagram path between source and
   destination, which performs other functions than just IP routing.  As
   outlined in [RFC3303], firewalls and NATs are potential obstacles to
   packet streams, for example, if dynamically negotiated UDP or TCP
   port numbers are used, as in many peer-to-peer communication
   applications.

   As one possible solution for this problem, the IETF MIDCOM working
   group defined a framework [RFC3303], requirements [RFC3304], and
   protocol semantics [RFC5189] for communication between applications
   and middleboxes acting as firewalls, NATs, or a combination of both.
   The MIDCOM architecture and framework define a model in which trusted
   third parties can be delegated to assist middleboxes in performing
   their operations, without requiring application intelligence being
   embedded in the middleboxes.  This trusted third party is referred to
   as the MIDCOM agent.  The MIDCOM protocol is defined between a MIDCOM
   agent and a middlebox.



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   The managed objects defined in this document can be used for
   dynamically configuring middleboxes on the datagram path to permit
   datagrams traversing the middleboxes.  This way, applications can,
   for example, request pinholes at firewalls and address bindings at
   NATs.

   Besides managed objects for controlling the middlebox operation, this
   document also defines managed objects that provide information on
   middlebox resource usage (such as firewall pinholes, NAT bindings,
   NAT sessions, etc.) affected by requests.

   Since firewalls and NATs are critical devices concerning network
   security, security issues of middlebox communication need to be
   considered very carefully.

3.1.  Terminology

   The terminology used in this document is fully aligned with the
   terminology defined in [RFC5189] except for the term 'MIDCOM agent'.
   For this term, there is a conflict between the MIDCOM terminology and
   the SNMP terminology.  The roles of entities participating in SNMP
   communication are called 'manager' and 'agent' with the agent acting
   as server for requests from the manager.  This use of the term
   'agent' is different from its use in the MIDCOM framework: The SNMP
   manager corresponds to the MIDCOM agent and the SNMP agent
   corresponds to the MIDCOM middlebox, also called MIDCOM server.  In
   order to avoid confusion in this document specifying a MIB module, we
   replace the term 'MIDCOM agent' with 'MIDCOM client'.  Whenever the
   term 'agent' is used in this document, it refers to the SNMP agent.
   Figure 1 sketches the entities of MIDCOM in relationship to SNMP
   manager and SNMP agent.

                  +---------+     MIDCOM      +-----------+
                  | MIDCOM  |<~ ~ ~ ~ ~ ~ ~ ~>|  MIDCOM   |
                  | Client  |   Transaction   | middlebox |
                  |         |                 | (server)  |
                  +---------+                 +-----------+
                       ^                            ^
                       |                            |
                       v                            v
                  +---------+                 +-----------+
                  |  SNMP   |      SNMP       |   SNMP    |
                  | Manager |<===============>|   Agent   |
                  +---------+    Protocol     +-----------+

                    Figure 1: Mapping of MIDCOM to SNMP





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4.  Realizing the MIDCOM Protocol with SNMP

   In order to realize middlebox communication as described in
   [RFC5189], several aspects and properties of the MIDCOM protocol need
   to be mapped to SNMP capabilities and expressed in terms of the
   Structure of Management Information version 2 (SMIv2).

   Basic concepts to be mapped are MIDCOM sessions and MIDCOM
   transactions.  For both, access control policies need to be
   supported.

4.1.  MIDCOM Sessions

   SNMP has no direct support for sessions.  Therefore, they need to be
   modeled.  A MIDCOM session is stateful and has a context that is
   valid for several transactions.  For SNMP, a context is valid for a
   single transaction only, for example, covering just a single
   request/reply pair of messages.

   Properties of sessions that are utilized by the MIDCOM semantics and
   not available in SNMP need to be modeled.  Particularly, the
   middlebox needs to be able to authenticate MIDCOM clients, authorize
   access to policy rules, and send notification messages concerning
   policy rules to MIDCOM clients participating in a session.  In the
   MIDCOM-MIB module, authentication and access control are performed on
   a per-message basis using an SNMPv3 security model, such as the
   User-based Security Model (USM) [RFC3414], for authentication, and
   the View-based Access Control Model (VACM) [RFC3415] for access
   control.  Sending notifications to MIDCOM clients is controlled by
   access control models such as VACM and a mostly static configuration
   of objects in the SNMP-TARGET-MIB [RFC3413] and the SNMP-
   NOTIFICATION-MIB [RFC3413].

   This session model is static except that the MIDCOM client can switch
   on and off the generation of SNMP notifications that the middlebox
   sends.  Recommended configurations of VACM and the SNMP-TARGET-MIB
   and the SNMP-NOTIFICATION-MIB that can serve for modeling a session
   are described in detail in section 6.

4.1.1.  Authentication and Authorization

   MIDCOM sessions are required for providing authentication,
   authorization, and encryption for messages exchanged between a MIDCOM
   client and a middlebox.  SNMPv3 provides these features on a per-
   message basis instead of a per-session basis applying a security
   model and an access control model, such as USM and VACM.  Per-message





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   security mechanisms can be considered as overhead compared to per-
   session security mechanisms, but it certainly satisfies the security
   requirements of middlebox communication.

   For each authenticated MIDCOM client, access to the MIDCOM-MIB,
   particularly to policy rules, should be configured as part of the
   VACM configuration of the SNMP agent.

4.2.  MIDCOM Transactions

   [RFC5189] defines the MIDCOM protocol semantics in terms of
   transactions and transaction parameters.  Transactions are grouped
   into request-reply transactions and asynchronous transactions.

   SNMP offers simple transactions that in general cannot be mapped
   one-to-one to MIDCOM transactions.  This section describes how the
   MIDCOM-MIB module implements MIDCOM transactions using SNMP
   transactions.  The concerned MIDCOM transactions are asynchronous
   transactions and request-reply transactions.  Within the set of
   request-reply transactions, we distinguish configuration transactions
   and monitoring transactions, because they are implemented in slightly
   different ways by using SNMP transactions.

   The SNMP terminology as defined in [RFC3411] does not use the concept
   of transactions, but of SNMP operations.  For the considerations in
   this section, we use the terms SNMP GET transaction and SNMP SET
   transaction.  An SNMP GET transaction consists of an SNMP Read Class
   operation and an SNMP Response Class operation.  An SNMP SET
   transaction consists of an SNMP Write Class operation and an SNMP
   Response Class operation.

4.2.1.  Asynchronous Transactions

   Asynchronous transactions can easily be modeled by SNMP Notification
   Class operations.  An asynchronous transaction contains a
   notification message with one to three parameters.  The message can
   be realized as an SNMP Notification Class operation with the
   parameters implemented as managed objects contained in the
   notification.












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               +--------------+  notification +------------+
               | MIDCOM client|<--------------| middlebox  |
               +--------------+    message    +------------+

                      MIDCOM asynchronous transaction


               +--------------+      SNMP     +------------+
               | SNMP manager |<--------------| SNMP agent |
               +--------------+  notification +------------+

             Implementation of MIDCOM asynchronous transaction

                 Figure 2: MIDCOM asynchronous transaction
                mapped to SNMP Notification Class operation

   One of the parameters is the transaction identifier that should be
   unique per middlebox.  It does not have to be unique for all
   notifications sent by the particular SNMP agent, but for all sent
   notifications that are defined by the MIDCOM-MIB module.

   Note that SNMP notifications are usually sent as unreliable UDP
   packets and may be dropped before they reach their destination.  If a
   MIDCOM client is expecting an asynchronous notification on a specific
   transaction, it would be the job of the MIDCOM client to poll the
   middlebox periodically and monitor the transaction in case
   notifications are lost along the way.

4.2.2.  Configuration Transactions

   All request-reply transactions contain a request message, a reply
   message, and potentially also a set of notifications.  In general,
   they cannot be modeled by just having a single SNMP message per
   MIDCOM message, because some of the MIDCOM messages carry a large set
   of parameters that do not necessarily fit into an SNMP message
   consisting of a single UDP packet only.

   For configuration transactions, the MIDCOM request message can be
   modeled by one or more SNMP SET transactions.  The action of sending
   the MIDCOM request to the middlebox is realized by writing the
   parameters contained in the message to managed objects at the SNMP
   agent.  If necessary, the SNMP SET transaction includes creating
   these managed objects.  If not all parameters of the MIDCOM request
   message can be set by a single SNMP SET transaction, then more than
   one SET transaction is used; see Figure 3.  Completion of the last of
   the SNMP transactions indicates that all required parameters are set
   and that processing of the MIDCOM request message can start at the
   middlebox.



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   Please note that a single SNMP SET transaction consists of an SNMP
   SET request message and an SNMP SET reply message.  Both are sent as
   unreliable UDP packets and may be dropped before they reach their
   destination.  If the SNMP SET request message or the SNMP reply
   message is lost, then the SNMP manager (the MIDCOM client) needs to
   take action, for example, by just repeating the SET transaction or by
   first checking the success of the initial write transaction with an
   SNMP GET transaction and then only repeating the SNMP SET transaction
   if necessary.

               +--------------+    request    +------------+
               | MIDCOM client|-------------->| middlebox  |
               +--------------+    message    +------------+

                          MIDCOM request message


               +--------------+               +------------+
               |              |    SNMP SET   |            |
               |              |-------------->|            |
               |              |    message    |            |
               |              |               |            |
               |              |    SNMP SET   |            |
               |              |<--------------|            |
               |              | reply message |            |
               | SNMP manager |               | SNMP agent |
               |              |    SNMP SET   |            |
               |              |- - - - - - - >|            |
               |              |    message    |            |
               |              |               |            |
               |              |    SNMP SET   |            |
               |              |< - - - - - - -|            |
               |              | reply message |            |
               |              |               |            |
               |              |  . . .        |            |
               +--------------+               +------------+

                 Implementation of MIDCOM request message
                   by one or more SNMP SET transactions

                     Figure 3: MIDCOM request message
                      mapped to SNMP SET transactions

   The MIDCOM reply message can be modeled in two ways.  The first way
   is an SNMP Notification Class operation optionally followed by one or
   more SNMP GET transactions as shown in Figure 4.  The MIDCOM server
   informs the MIDCOM client about the end of processing the request by
   sending an SNMP notification.  If possible, the SNMP notification



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   carries all reply parameters.  If this is not possible, then the SNMP
   manager has to perform additional SNMP GET transactions as long as
   necessary to receive all of the reply parameters.

               +--------------+     reply     +------------+
               | MIDCOM client|<--------------| middlebox  |
               +--------------+    message    +------------+

                           MIDCOM reply message


               +--------------+               +------------+
               |              |     SNMP      |            |
               |              |<--------------|            |
               |              |  notification |            |
               |              |               |            |
               |              |    SNMP GET   |            |
               |              |-------------->|            |
               |              |    message    |            |
               | SNMP manager |               | SNMP agent |
               |              |    SNMP GET   |            |
               |              |<--------------|            |
               |              | reply message |            |
               |              |               |            |
               |              |    SNMP GET   |            |
               |              |- - - - - - - >|            |
               |              |    message    |            |
               |              |               |            |
               |              |    SNMP GET   |            |
               |              |< - - - - - - -|            |
               |              | reply message |            |
               |              |               |            |
               |              |  . . .        |            |
               +--------------+               +------------+

                  Implementation of MIDCOM reply message
                          by an SNMP notification
                   and one or more SNMP GET transactions

                      Figure 4: MIDCOM reply message
         mapped to SNMP notification and optional GET transactions

   The second way replaces the SNMP Notification Class operation by a
   polling operation of the SNMP manager.  The manager polls status
   information at the SNMP agent using SNMP GET transactions until it
   detects the end of the processing of the request.  Then it uses one
   or more SNMP GET transactions to receive all of the reply parameters.
   Note that this second way requires more SNMP operations, but is more



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   reliable than the first way using an SNMP Notification Class
   operation.

4.2.3.  Monitoring Transactions

   The realization of MIDCOM monitoring transactions in terms of SNMP
   transactions is simpler.  The request message is very short and just
   specifies a piece of information that the MIDCOM client wants to
   retrieve.

               +--------------+    request    +------------+
               |              |-------------->|            |
               |              |    message    |            |
               | MIDCOM client|               | middlebox  |
               |              |     reply     |            |
               |              |<--------------|            |
               +--------------+    message    +------------+

                       MIDCOM monitoring transaction


               +--------------+               +------------+
               |              |    SNMP GET   |            |
               |              |-------------->|            |
               |              |    message    |            |
               |              |               |            |
               |              |    SNMP GET   |            |
               |              |<--------------|            |
               |              | reply message |            |
               | SNMP manager |               | SNMP agent |
               |              |    SNMP GET   |            |
               |              |- - - - - - - >|            |
               |              |    message    |            |
               |              |               |            |
               |              |    SNMP GET   |            |
               |              |< - - - - - - -|            |
               |              | reply message |            |
               |              |               |            |
               |              |  . . .        |            |
               +--------------+               +------------+

              Implementation of MIDCOM monitoring transaction
                     by one or more SNMP GET messages

                  Figure 5: MIDCOM monitoring transaction
                      mapped to SNMP GET transactions





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   Since monitoring is a strength of SNMP, there are sufficient means to
   realize MIDCOM monitoring transactions simpler than MIDCOM
   configuration transactions.

   All MIDCOM monitoring transactions can be realized as a sequence of
   SNMP GET transactions.  The number of SNMP GET transactions required
   depends on the amount of information to be retrieved.

4.2.4.  Atomicity of MIDCOM Transactions

   Given the realizations of MIDCOM transactions by means of SNMP
   transactions, atomicity of the MIDCOM transactions is not fully
   guaranteed anymore.  However, this section shows that atomicity
   provided by the MIB module specified in section 9 is still sufficient
   for meeting the MIDCOM requirements specified in [RFC3304].

4.2.4.1.  Asynchronous MIDCOM Transactions

   There are two asynchronous MIDCOM transactions: Asynchronous Session
   Termination (AST) and Asynchronous Policy Rule Event (ARE).  The very
   static realization of MIDCOM sessions in the MIDCOM-MIB, as described
   by section 4.1, does not anymore support the asynchronous termination
   of a session.  Therefore, the AST transaction is not modeled.  For
   the ARE, atomicity is maintained, because it is modeled by a single
   atomic SNMP notification transaction.

   In addition, the MIDCOM-MIB supports an Asynchronous Group Event
   transaction, which is an aggregation of a set of ARE transactions.
   Also, this MIDCOM transaction is implemented by a single SNMP
   transaction.

4.2.4.2.  Session Establishment and Termination Transactions

   The MIDCOM-MIB models MIDCOM sessions in a very static way.  The only
   dynamic actions within these transactions are enabling and disabling
   the generation of SNMP notifications at the SNMP agent.

   For the Session Establishment (SE) transaction, the MIDCOM client
   first reads the middlebox capabilities.  It is not relevant whether
   or not this action is atomic because a dynamic change of the
   middlebox capabilities is not to be expected.  Therefore, also non-
   atomic implementations of this action are acceptable.

   Then, the MIDCOM agent needs to enable the generation of SNMP
   notifications at the middlebox.  This can be realized by writing to a
   single managed object in the SNMP-NOTIFICATION-MIB [RFC3413].  But
   even other implementations are acceptable, because atomicity is not
   required for this step.



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   For the Session Termination (ST) transaction, the only required
   action is disabling the generation of SNMP notifications at the
   middlebox.  As for the SE transaction, this action can be realized
   atomically by using the SNMP-NOTIFICATION-MIB, but also other
   implementations are acceptable because atomicity is not required for
   this action.

4.2.4.3.  Monitoring Transactions

   Potentially, the monitoring transactions Policy Rule List (PRL),
   Policy Rule Status (PRS), Group List (GL), and Group Status (GS) are
   not atomic, because these transactions may be implemented by more
   than one SNMP GET operation.

   The problem that might occur is that while the monitoring transaction
   is performed, the monitored items may change.  For example, while
   reading a long list of policies, new policies may be added and
   already read policies may be deleted.  This is not in line with the
   protocol semantics.  However, it is not in direct conflict with the
   MIDCOM requirement requesting the middlebox state to be stable and
   known by the MIDCOM client, because the middlebox notifies the MIDCOM
   client on all changes to its state that are performed during the
   monitoring transaction by sending notifications.

   If the MIDCOM client receives such a notification while performing a
   monitoring transaction (or shortly after completing it), the MIDCOM
   client can then either repeat the monitoring transaction or integrate
   the result of the monitoring transaction with the information
   received via notifications during the transaction.  In both cases,
   the MIDCOM client will know the state of the middlebox.

4.2.4.4.  Lifetime Change Transactions

   For the policy Rule Lifetime Change (RLC) transaction and the Group
   Lifetime Change (GLC) transaction, atomicity is maintained.  They
   both have very few parameters for the request message and the reply
   message.  The request parameters can be transmitted by a single SNMP
   SET request message, and the reply parameters can be transmitted by a
   single SNMP notification message.  In order to prevent idempotency
   problems by retransmitting an SNMP request after a lost SNMP reply,
   it is RECOMMENDED that either snmpSetSerialNo (see [RFC3418]) is
   included in the corresponding SNMP SET request or the value of the
   SNMP retransmission timer be lower than the smallest requested
   lifetime value.  The same recommendation applies to the smallest
   requested value for the midcomRuleStorageTime.  MIDCOM client
   implementations MAY completely avoid this problem by configuring
   their SNMP stack such that no retransmissions are sent.




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4.2.4.5.  Transactions Establishing New Policy Rules

   Analogous to the monitoring transactions, the atomicity may not be
   given for Policy Reserve Rule (PRR) and Policy Enable Rule (PER)
   transactions.  Both transactions are potentially implemented using
   more than one SNMP SET operation and GET operation for obtaining
   transaction reply parameters.  The solution for this loss of
   atomicity is the same as for the monitoring transactions.

   There is an additional atomicity problem for PRR and PER.  If
   transferring request parameters requires more than a single SET
   operation, then there is the potential problem that multiple MIDCOM
   clients sharing the same permissions are able to access the same
   policy rule.  In this case, a client could alter request parameters
   already set by another client before the first client could complete
   the request.  However, this is acceptable since usually only one
   agent is creating a policy rule and filling it subsequently.  It can
   also be assumed that in most cases where clients share permissions,
   they act in a more or less coordinated way avoiding such
   interferences.

   All atomicity problems caused by using multiple SNMP SET transactions
   for implementing the MIDCOM request message can be avoided by
   transferring all request parameters with a single SNMP SET
   transaction.

4.2.5.  Access Control

   Since SNMP does not offer per-session authentication and
   authorization, authentication and authorization are performed per
   SNMP message sent from the MIDCOM client to the middlebox.

   For each transaction, the MIDCOM client has to authenticate itself as
   an authenticated principal, such as a USM user.  Then, the
   principal's access rights to all resources affected by the
   transaction are checked.  Access right control is realized by
   configuring the access control mechanisms, such as VACM, at the SNMP
   agent.

4.3.  Access Control Policies

   Potentially, a middlebox has to control access for a large set of
   MIDCOM clients and to a large set of policy rules configuring
   firewall pinholes and NAT bindings.  Therefore, it can be beneficial
   to use access control policies for specifying access control rules.
   Generating, provisioning, and managing these policies are out of
   scope of this MIB module.




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   However, if such an access control policy system is used, then the
   SNMP agent acts as a policy enforcement point.  An access control
   policy system must transform all active policies into configurations
   of, for example, the SNMP agent's View-based Access Control Model
   (VACM).

   The mechanisms of access control models, such as VACM, allow an
   access control policy system to enforce MIDCOM client authentication
   rules and general access control of MIDCOM clients to middlebox
   control.

   The mechanisms of VACM can be used to enforce access control of
   authenticated clients to MIDCOM-MIB policy rules based on the concept
   of ownership.  For example, an access control policy can specify that
   MIDCOM-MIB policy rules owned by user A cannot be accessed at all by
   user B, can be read by user C, and can be read and modified by user
   D.

   Further access control policies can control access to concrete
   middlebox resources.  These are enforced, when a MIDCOM request is
   processed.  For example, an authenticated MIDCOM client may be
   authorized to request new MIDCOM policies to be established, but only
   for certain IP address ranges.  The enforcement of this kind of
   policies may not be realizable using available SNMP mechanisms, but
   needs to be performed by the individual MIB module implementation.

5.  Structure of the MIB Module

   The MIB module defined in section 9 contains three kinds of managed
   objects:

   -   Transaction objects
       Transaction objects are required for implementing the MIDCOM
       protocol requirements defined in [RFC3304] and the MIDCOM
       protocol semantics defined in [RFC5189].

   -   Configuration objects
       Configuration objects can be used for retrieving middlebox
       capability information (mandatory) and for setting parameters of
       the implementation of transaction objects (optional).

   -   Monitoring objects
       The optional monitoring objects provide information about used
       resources and about MIDCOM transaction statistics.

   The transaction objects are organized in two tables: the
   midcomRuleTable and the midcomGroupTable.  Entity relationships of




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   entries of these tables and the midcomResourceTable from the
   monitoring objects are illustrated by Figure 6.

                            +--------------------+
                            |  midcomRuleEntry   |
                            |     indexed by     |
                            |  midcomRuleOwner   |
                            |  midcomGroupIndex  |
                            |  midcomRuleIndex   |
                            +--------------------+
                        1...n |                | 1
                              |                |
                            1 |                | 1
           +--------------------+            +---------------------+
           |  midcomGroupEntry  |            | midcomResourceEntry |
           |     indexed by     |            |     indexed by      |
           |  midcomRuleOwner   |            |  midcomRuleOwner    |
           |  midcomGroupIndex  |            |  midcomGroupIndex   |
           +--------------------+            |  midcomRuleIndex    |
                                             +---------------------+
                                               |        |        |
                                               |        |        |
                                               v        v        v
                                              NAT   Firewall   other
                                              MIB      MIB      MIB

              Figure 6: Entity relationships of table entries

   A MIDCOM client can create and delete entries in the midcomRuleTable.
   Entries in the midcomGroupTable are generated automatically as soon
   as there is an entry in the midcomRuleTable using the
   midcomGroupIndex.  The midcomGroupTable can be used as shortcut for
   accessing all member rules with a single transaction.  MIDCOM clients
   can group policy rules for various purposes.  For example, they can
   assign a unique value for the midcomGroupIndex to all rules belonging
   to a single application or an application session served by the
   MIDCOM agent.

   The midcomResourceTable augments the midcomRuleTable by information
   on the relationship of entries of the midcomRuleTable to resources
   listed in other MIB modules, such as the NAT-MIB [RFC4008].

5.1.  Transaction Objects

   The transaction objects are structured according to the MIDCOM
   semantics described in [RFC5189] into two subtrees, one for policy
   rule control and one for policy rule group control.




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5.1.1.  midcomRuleTable

   The midcomRuleTable contains information about policy rules including
   policy rules to be established, policy rules for which establishing
   failed, established policy rules, and terminated policy rules.

   Entries in this table are indexed by the combination of
   midcomRuleOwner, midcomGroupIndex, and midcomRuleIndex.  The
   midcomRuleOwner is the owner of the rule; the midcomGroupIndex is the
   index of the group of which the policy rule is a member.

   midcomRuleOwner is of type SnmpAdminString, a textual convention that
   allows for use of the SNMPv3 View-based Access Control Model (VACM
   [RFC3415]) and allows a management application to identify its
   entries.

   Entries in this table are created by writing to midcomRuleRowStatus.
   Entries are removed when both their midcomRuleLifetime and
   midcomRuleStorageTime are timed out by counting down to 0.  A MIDCOM
   client can explicitly remove an entry by setting midcomRuleLifetime
   and midcomRuleStorageTime to 0.

   The table contains the following columnar objects:

   o   midcomRuleIndex
       The index of this entry must be unique in combination with the
       midcomRuleOwner and the midcomGroupIndex of the entry.

   o   midcomRuleAdminStatus
       For establishing a new policy rule, a set of objects in this
       entry needs to be written first.  These objects are the request
       parameters.  Then, by writing either reserve(1) or enable(2) to
       this object, the MIDCOM-MIB implementation is triggered to start
       processing the parameters and tries to establish the specified
       policy rule.

   o   midcomRuleOperStatus
       This read-only object indicates the current status of the entry.
       The entry may have an initializing state, it may have a transient
       state while processing requests, it may have an error state after
       a request was rejected, it may have a state where a policy rule
       is established, or it may have a terminated state.

   o   midcomRuleStorageType
       This object indicates whether or not the policy rule is stored as
       volatile, non-volatile, or permanent.  Depending on the MIDCOM-
       MIB implementation, this object may be writable.




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   o   midcomRuleStorageTime
       This object indicates how long the entry will still exist after
       entering an error state or a termination state.

   o   midcomRuleError
       This object is a string indicating the reason for entering an
       error state.

   o   midcomRuleInterface
       This object indicates the IP interface for which enforcement of a
       policy rule is requested or performed, respectively.

   o   midcomRuleFlowDirection
       This object indicates a flow direction for which a policy enable
       rule was requested or established, respectively.

   o   midcomRuleMaxIdleTime
       This object indicates the maximum idle time of the policy rule in
       seconds.  If no packet to which the policy rule applies passes
       the middlebox for the time specified by midcomRuleMaxIdleTime,
       then the policy rule enters a termination state.

   o   midcomRuleTransportProtocol
       This object indicates a transport protocol for which a policy
       reserve rule or policy enable rule was requested or established,
       respectively.

   o   midcomRulePortRange
       This object indicates a port range for which a policy reserve
       rule or policy enable rule was requested or established,
       respectively.

   o   midcomRuleLifetime
       This object indicates the remaining lifetime of an established
       policy rule.  The MIDCOM client can change the remaining lifetime
       by writing to it.

   Beyond the listed objects, the table contains 10 further objects
   describing address parameters.  They include the IP version, IP
   address, prefix length and port number for the internal address (A0),
   inside address (A1), outside address (A2), and external address (A3).
   These objects serve as parameters specifying a request or an
   established policy, respectively.

   A0, A1, A2, and A3 are address tuples defined according to the MIDCOM
   semantics [RFC5189].  Each of them identifies either a communication
   endpoint at an internal or external device or an allocated address at
   the middlebox.



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         +----------+                                 +----------+
         | internal | A0    A1 +-----------+ A2    A3 | external |
         | endpoint +----------+ middlebox +----------+ endpoint |
         +----------+          +-----------+          +----------+

                     Figure 7: Address tuples A0 - A3

    - A0 - internal endpoint: Address tuple A0 specifies a communication
      endpoint of a device within the internal network, with respect to
      the middlebox.

    - A1 - middlebox inside address: Address tuple A1 specifies a
      virtual communication endpoint at the middlebox within the
      internal network.  A1 is the destination address for packets
      passing from the internal endpoint to the middlebox and is the
      source for packets passing from the middlebox to the internal
      endpoint.

    - A2 - middlebox outside address: Address tuple A2 specifies a
      virtual communication endpoint at the middlebox within the
      external network.  A2 is the destination address for packets
      passing from the external endpoint to the middlebox and is the
      source for packets passing from the middlebox to the external
      endpoint.

    - A3 - external endpoint: Address tuple A3 specifies a communication
      endpoint of a device within the external network, with respect to
      the middlebox.

   The MIDCOM-MIB requires the MIDCOM client to specify address tuples
   A0 and A3.  This might be a problem for applications that are not
   designed in a firewall-friendly way.  An example is an FTP
   application that uses the PORT command (instead of the recommended
   PASV command).  The problem only occurs when the middlebox offers
   twice-NAT functionality, and it can be fixed following
   recommendations for firewall-friendly communication.

5.1.2.  midcomGroupTable

   The midcomGroupTable has an entry per existing policy rule group.
   Entries in this table are created automatically when creating member
   entries in the midcomRuleTable.  Entries are automatically removed
   from this table when the last member entry is removed from the
   midcomRuleTable.  Entries cannot be created or removed explicitly by
   the MIDCOM client.






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   Entries are indexed by the midcomRuleOwner of the rules that belong
   to the group and by a specific midcomGroupIndex.  This allows each
   midcomRuleOwner to maintain its own independent group namespace.

   An entry of the table contains the following objects:

   o   midcomGroupIndex
       The index of this entry must be unique in combination with the
       midcomRuleOwner of the entry.

   o   midcomGroupLifetime
       This object indicates the maximum of the remaining lifetimes of
       all established policy rules that are members of the group.  The
       MIDCOM client can change the remaining lifetime of all member
       policies by writing to this object.

5.2.  Configuration Objects

   The configuration subtree contains middlebox capability and
   configuration information.  Some of the contained objects are
   (optionally) writable and can also be used for configuring the
   middlebox service.

   The capabilities subtree contains some general capability information
   and detailed information per supported IP interface.  The
   midcomConfigFirewallTable can be used to configure how the MIDCOM-MIB
   implementation creates firewall rules in its firewall modules.

   Note that typically, configuration objects are not intended to be
   written by MIDCOM clients.  In general, write access to these objects
   needs to be restricted more strictly than write access to transaction
   objects.

5.2.1.  Capabilities

   Information on middlebox capabilities, i.e., capabilities of the
   MIDCOM-MIB implementation, is provided by the midcomCapabilities
   subtree of managed objects.  The following objects are defined:

   o   midcomConfigMaxLifetime
       This object indicates the maximum lifetime that this middlebox
       allows policy rules to have.

   o   midcomConfigPersistentRules
       This is a boolean object indicating whether or not the middlebox
       is capable of storing policy rules persistently.





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       Further capabilities are provided by the midcomConfigIfTable per
       IP interface.  This table contains just two objects.  The first
       one is a BITS object called midcomConfigIfBits containing the
       following bit values:

   o   ipv4 and ipv6
       These two bit values provide information on which IP versions are
       supported by the middlebox at the indexed interface.

   o   addressWildcards and portWildcards
       These two bit values provide information on wildcarding supported
       by the middlebox at the indexed interface.

   o   firewall and nat
       These two bit values provide information on availability of
       firewall and NAT functionality at the indexed interface.

   o   portTranslation, protocolTranslation, and twiceNat
       These three bit values provide information on the kind of NAT
       functionality available at the indexed interface.

   o   inside
       This bit indicates whether or not the indexed interface is an
       inside interface with respect to NAT functionality.

   The second object, called midcomConfigIfEnabled, indicates whether
   the middlebox capabilities described by midcomConfigIfBits are
   available or not available at the indexed IP interface.

   The midcomConfigIfTable uses index 0 for indicating capabilities that
   are available for all interfaces.

5.2.2.  midcomConfigFirewallTable

   The midcomConfigFirewallTable serves for configuring how policy rules
   created by MIDCOM clients are realized as firewall rules of a
   firewall implementation.  Particularly, the priority used for
   MIDCOM-MIB policy rules can be configured.  For a single firewall
   implementation at a particular IP interface, all MIDCOM-MIB policy
   rules are realized as firewall rules with the same priority.  Also, a
   firewall rule group name can be configured.  The table is indexed by
   the IP interface index.

   An entry of the table contains the following objects:

   o   midcomConfigFirewallGroupId
       This object indicates the firewall rule group to which all
       firewall rules of the MIDCOM server are assigned.



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   o   midcomConfigFirewallPriority
       This object indicates the priority assigned to all firewall rules
       of the MIDCOM server.

5.3.  Monitoring Objects

   The monitoring objects are structured into two subtrees: the resource
   subtree and the statistics subtree.  The resource subtree provides
   information about which resources are used by which policy rule.  The
   statistics subtree provides statistics about the usage of transaction
   objects.

5.3.1.  midcomResourceTable

   Information about resource usage per policy rule is provided by the
   midcomResourceTable.  Each entry in the midcomResourceTable describes
   resource usage of exactly one policy rule.

   Resources are NAT resources and firewall resources, depending on the
   type of middlebox.  Used NAT resources include NAT bindings and NAT
   sessions.  NAT address mappings are not covered.  For firewalls,
   firewall filter rules are considered as resources.

   The values provided by the following objects on NAT binds and NAT
   sessions may refer to the detailed resource usage description in the
   NAT-MIB module [RFC4008].

   The values provided by the following objects on firewall rules may
   refer to more detailed firewall resource usage descriptions in other
   MIB modules.

   Entries in the midcomResourceTable are only valid if the
   midcomRuleOperStatus object of the corresponding entry in the
   midcomRuleTable has a value of either reserved(7) or enabled(8).

   An entry of the table contains the following objects:

   o   midcomRscNatInternalAddrBindMode
       This object indicates whether the binding of the internal address
       is an address NAT binding or an address-port NAT binding.

   o   midcomRscNatInternalAddrBindId
       This object identifies the NAT binding for the internal address
       in the NAT engine.

   o   midcomRscNatExternalAddrBindMode
       This object indicates whether the binding of the external address
       is an address NAT binding or an address-port NAT binding.



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   o   midcomRscNatExternalAddrBindId
       This object identifies the NAT binding for the external address
       in the NAT engine.

   o   midcomRscNatSessionId1
       This object links to the first NAT session associated with one of
       the above NAT bindings.

   o   midcomRscNatSessionId2
       This object links to the optional second NAT session associated
       with one of the above NAT bindings.

   o   midcomRscFirewallRuleId
       This object indicates the firewall rule for this policy rule.

   The MIDCOM-MIB module does not require a middlebox to implement
   further specific middlebox (NAT, firewall, etc.) MIB modules as, for
   example, the NAT-MIB module [RFC4008].

   The resource identifiers in the midcomResourceTable may be vendor
   proprietary in the cases where the middlebox does not implement the
   NAT-MIB [RFC4008] or a firewall MIB.  The MIDCOM-MIB module affects
   NAT binding and sessions, as well as firewall pinholes.  It is
   intentionally not specified in the MIDCOM-MIB module how these NAT
   and firewall resources are allocated and managed, since this depends
   on the MIDCOM-MIB implementation and middlebox's capabilities.
   However, the midcomResourceTable is useful for understanding which
   resources are affected by which MIDCOM-MIB transaction.

   The midcomResourceTable is beneficial to the middlebox administrator
   in that the table lists all MIDCOM transactions and the middlebox
   specific resources to which these transactions refer.  For instance,
   multiple MIDCOM clients might end up using the same NAT bind, yet
   each MIDCOM client might define a Lifetime parameter and
   directionality for the bind that is specific to the transaction.
   MIDCOM-MIB implementations are responsible for impacting underlying
   middlebox resources so as to satisfy the sometimes overlapping
   requirements on the same resource from multiple MIDCOM clients.

   Managing these resources is not a trivial task for MIDCOM-MIB
   implementers.  It is possible that different MIDCOM-MIB policy rules
   owned by different MIDCOM clients share a NAT binding or a firewall
   rule.  Then common properties, for example, the lifetime of the
   resource, need to be managed such that all clients are served well
   and changes to these resources need to be communicated to all
   affected clients.  Also, dependencies between resources, for example,
   the precedence order of firewall rules, need to be considered




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   carefully in order to avoid that different policy rules --
   potentially owned by different clients -- influence each other.

   MIDCOM clients may use the midcomResourceTable of the MIDCOM-MIB
   module in conjunction with the NAT-MIB module [RFC4008] to determine
   which resources of the NAT are used for MIDCOM.  The NAT-MIB module
   stores the configured NAT bindings and sessions, and MIDCOM clients
   can use the information of the midcomResourceTable to sort out those
   NAT resources that are used by the MIDCOM-MIB module.

5.3.2.  midcomStatistics

   The statistics subtree contains a set of non-columnar objects that
   provide 'MIDCOM protocol statistics', i.e., statistics about the
   usage of transaction objects.

   o   midcomCurrentOwners
       This object indicates the number of different values for
       midcomRuleOwner for all current entries in the midcomRuleTable.

   o   midcomOwnersTotal
       This object indicates the summarized number of all different
       values that occurred for midcomRuleOwner in the midcomRuleTable
       current and in the past.

   o   midcomTotalRejectedRuleEntries
       This object indicates the total number of failed attempts to
       create an entry in the midcomRuleTable.

   o   midcomCurrentRulesIncomplete
       This object indicates the total number of policy rules that have
       not been fully loaded into a table row of the midcomRuleTable.

   o   midcomTotalIncorrectReserveRules
       This object indicates the total number of policy reserve rules
       that were rejected because the request was incorrect.

   o   midcomTotalRejectedReserveRules
       This object indicates the total number of policy reserve rules
       that were failed while being processed.

   o   midcomCurrentActiveReserveRules
       This object indicates the number of currently active policy
       reserve rules in the midcomRuleTable.

   o   midcomTotalExpiredReserveRules
       This object indicates the total number of expired policy reserve
       rules.



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   o   midcomTotalTerminatedOnRqReserveRules
       This object indicates the total number of policy reserve rules
       that were terminated on request.

   o   midcomTotalTerminatedReserveRules
       This object indicates the total number of policy reserve rules
       that were terminated, but not on request.

   o   midcomTotalIncorrectEnableRules
       This object indicates the total number of policy enable rules
       that were rejected because the request was incorrect.

   o   midcomTotalRejectedEnableRules
       This object indicates the total number of policy enable rules
       that were failed while being processed.

   o   midcomCurrentActiveEnableRules
       This object indicates the number of currently active policy
       enable rules in the midcomRuleTable.

   o   midcomTotalExpiredEnableRules
       This object indicates the total number of expired policy enable
       rules.

   o   midcomTotalTerminatedOnRqEnableRules
       This object indicates the total number of policy enable rules
       that were terminated on request.

   o   midcomTotalTerminatedEnableRules
       This object indicates the total number of policy enable rules
       that were terminated, but not on request.

5.4.  Notifications

   For informing MIDCOM clients about state changes of MIDCOM-MIB
   implementations, three notifications can be used.  They notify the
   MIDCOM client about state changes of individual policy rules or of
   groups of policy rules.  Different notifications are used for
   different kinds of transactions.

   For asynchronous transactions, unsolicited notifications are used.
   The only asynchronous transaction that needs to be modeled by the
   MIDCOM-MIB is the Asynchronous Policy Rule Event (ARE).  The ARE may
   be caused by the expiration of a policy rule lifetime, the expiration
   of the idle time, or an internal change in policy rule lifetime by
   the MIDCOM-MIB implementation for whatever reason.





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   For configuration transactions, solicited notifications are used.
   This concerns the Policy Reserve Rule (PRR) transaction, the Policy
   Enable Rule (PER) transaction, the Policy Rule Lifetime Change (RLC)
   transaction, and the Group Lifetime Change (GLC) transaction.

   The separation between unsolicited and solicited notifications gives
   the implementer of a MIDCOM client some freedom to make design
   decisions on how to model the MIDCOM reply message as described at
   the end of section 4.2.2.  Depending on the choice, processing of
   solicited notifications may not be required.  In such a case,
   delivery of solicited notification may be disabled, for example, by
   an appropriate configuration of the snmpNotifyFilterTable such that
   solicited notifications are filtered differently to unsolicited
   notifications.

   o   midcomUnsolicitedRuleEvent
       This notification can be generated for indicating the change of a
       policy rule's state or lifetime.  It is used for performing the
       ARE transaction.

   o   midcomSolicitedRuleEvent
       This notification can be generated for indicating the requested
       change of a policy rule's state or lifetime.  It is used for
       performing PRR, PER, and RLC transactions.

   o   midcomSolicitedGroupEvent
       This notification can be generated for indicating the requested
       change of a policy rule group's lifetime.  It is used for
       performing the GLC transaction.

6.  Recommendations for Configuration and Operation

   Configuring MIDCOM-MIB security is highly sensitive for obvious
   reasons.  This section gives recommendations for securely configuring
   the SNMP agent acting as MIDCOM server.  In addition, recommendations
   for avoiding idempotency problems are given and restrictions of
   MIDCOM-MIB applicability to a special set of applications are
   discussed.

6.1.  Security Model Configuration

   Since controlling firewalls and NATs is highly sensitive, it is
   RECOMMENDED that SNMP Command Responders implementing the MIDCOM-MIB
   module use the authPriv security level for all users that may access
   managed objects of the MIDCOM-MIB module.






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6.2.  VACM Configuration

   Entries in the midcomRuleTable and the midcomGroupTable provide
   information about existing firewall pinholes and/or NAT sessions.
   They also could be used for manipulating firewall pinholes and/or NAT
   sessions.  Therefore, access control to these objects is essential
   and should be restrictive.

   It is RECOMMENDED that SNMP Command Responders instantiating an
   implementation of the MIDCOM-MIB module use VACM for controlling
   access to managed objects in the midcomRuleTable and the
   midcomGroupTable.

   It is further RECOMMENDED that individual MIDCOM clients, acting as
   SNMP Command Generators, only have access to an entry in the
   midcomRuleTable, the midcomResourceTable, or the midcomGroupTable, if
   they created the entry directly in the midcomRuleTable or indirectly
   in the midcomGroupTable and midcomResourceTable.  Exceptions to this
   recommendation are situations where access by multiple MIDCOM clients
   to managed objects is explicitly required.  One example is fail-over
   for MIDCOM agents where the stand-by MIDCOM agent needs the same
   access rights to managed objects as the currently active MIDCOM
   agent.  Another example is a supervisor MIDCOM agent that monitors
   activities of other MIDCOM agents and/or may be used by network
   management systems to modify entries in tables of the MIDCOM-MIB.

   For this reason, all three tables listed above have the
   midcomRuleOwner as initial index.  It is RECOMMENDED that MIDCOM
   clients acting as SNMP Command Generator have access to the
   midcomRuleTable and the midcomGroupTable restricted to entries with
   the initial index matching either their SNMP securityName or their
   VACM groupName.  It is RECOMMENDED that they do not have access to
   entries in these tables with initial indices other than their SNMP
   securityName or their VACM groupName.  It is RECOMMENDED that this
   VACM configuration is applied to read access, write access, and
   notify access for all objects in the midcomRuleTable and the
   midcomGroupTable.

   Note that less restrictive access rights MAY be granted to other
   users, for example, to a network management application, that
   monitors MIDCOM policy rules.










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6.3.  Notification Configuration

   For each MIDCOM client that has access to the midcomRuleTable, a
   notification target SHOULD be configured at a Command Responder
   instantiating an implementation of the MIDCOM-MIB.  It is RECOMMENDED
   that such a configuration be retrievable from the Command Responder
   via the SNMP-TARGET-MIB [RFC3413].

   For each entry of the snmpTargetAddrTable that is related to a MIDCOM
   client, there SHOULD be an individual corresponding entry in the
   snmpTargetParamsTable.

   An implementation of the MIDCOM-MIB SHOULD also implement the SNMP-
   NOTIFICATION-MIB [RFC3413].  An instance of an implementation of the
   MIDCOM-MIB SHOULD have an individual entry in the
   snmpNotifyFilterProfileTable for each MIDCOM client that has access
   to the midcomRuleTable.

   An instance of an implementation of the MIDCOM-MIB SHOULD allow
   MIDCOM clients to start and stop the generation of notifications
   targeted at themselves.  This SHOULD be realized by giving the MIDCOM
   clients write access to the snmpNotifyFilterTable.  If appropriate
   entries of the snmpNotifyFilterTable are established in advance, then
   this can be achieved by granting MIDCOM clients write access only to
   the columnar object snmpNotifyFilterType.

   It is RECOMMENDED that VACM be configured such that each MIDCOM agent
   can only access entries in the snmpTargetAddrTable, the
   snmpTargetParamsTable, the snmpNotifyFilterProfileTable, and the
   snmpFilterTable that concern that particular MIDCOM agent.
   Typically, read access to the snmpTargetAddrTable, the
   snmpTargetParamsTable, and the snmpNotifyFilterProfileTable is
   sufficient.  Write access may be required for objects of the
   snmpFilterTable.

6.4.  Simultaneous Access

   Situations with two MIDCOM clients simultaneously modifying the same
   policy rule should be avoided.  For each entry in the
   midcomRuleTable, there should be only one client at a time that
   modifies it.  If two MIDCOM clients share the same midcomRuleOwner
   index of the midcomRuleTable, then conflicts can be avoided, for
   example, by

      - scheduling access times, as, for example, in the fail-over case;
      - using different midcomGroupIndex values per client; or
      - using non-overlapping intervals for values of the
        midcomRuleIndex per client.



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6.5.  Avoiding Idempotency Problems

   As already discussed in section 4.2.4.4, the following recommendation
   is given for avoiding idempotency problems.

   In general, idempotency problems can be solved by including
   snmpSetSerialNo (see [RFC3418]) in SNMP SET requests.

   In case this feature is not used, it is RECOMMENDED that the value of
   the SNMP retransmission timer of a MIDCOM client (acting as SNMP
   Command Generator) is lower than the smallest requested value for any
   rule lifetime or rule idle time in order to prevent idempotency
   problems with setting midcomRuleLifetime and midcomRuleMaxIdleTime
   when retransmitting an SNMP SET request after a lost SNMP reply.

   MIDCOM client implementations MAY completely avoid this problem by
   configuring their SNMP stack such that no retransmissions are sent.

   Similar considerations apply to MIDCOM-MIB implementations acting as
   Notification Originator when sending a notification
   (midcomUnsolicitedRuleEvent, midcomSolicitedRuleEvent or
   midcomSolicitedGroupEvent) containing the remaining lifetime of a
   policy rule or a policy rule group, respectively.

6.6.  Interface Indexing Problems

   A well-known problem of MIB modules is indexing IP interfaces after a
   re-initialization of the managed device.  The index for interfaces
   provided by the ifTable (see IF-MIB in [RFC2863]) may change during
   re-initialization, for example, when physical interfaces are added or
   removed.

   The MIDCOM-MIB module uses the interface index for indicating at
   which interface which policy rule is (or is to be) applied.  Also,
   this index is used for indicating how policy rules are prioritized at
   certain interfaces.  The MIDCOM-MIB module specification requires
   that information provided is always correct.  This implies that after
   re-initialization, interface index values of policy rules or firewall
   configurations may have changed even though they still refer to the
   same interface as before the re-initialization.

   MIDCOM client implementations need to be aware of this potential
   behavior.  It is RECOMMENDED that before writing the value or using
   the value of indices that depend on the ifTable the MIDCOM client
   checks if the middlebox has been re-initialized recently.






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   MIDCOM-MIB module implementations MUST track interface changes of IP
   interface indices in the ifTable.  This implies that after a re-
   initialization of a middlebox, a MIDCOM-MIB implementation MUST make
   sure that each instance of an interface index in the MIDCOM-MIB
   tables still points to the same interface as before the re-
   initialization.  For any instance for which this is not possible, all
   affected entries in tables of the MIDCOM-MIB module MUST be either
   terminated, disabled, or deleted, as specified in the DESCRIPTION
   clause of the respective object.  This concerns all objects in the
   MIDCOM-MIB module that are of type InterfaceIndexOrZero.

6.7.  Applicability Restrictions

   As already discussed in section 5.1.1, the MIDCOM-MIB requires the
   MIDCOM client to specify address tuples A0 and A3.  This can be a
   problem for applications that do not have this information available
   when they need to configure the middlebox.  For some applications,
   there are usage scenarios where address information is only available
   for a single address realm, A0 and A1 in the private realm or A2 and
   A3 in the public realm.  An example is an FTP application using the
   PORT command (instead of the PASV command).  The problem occurs when
   the middlebox offers twice-NAT functionality.

7.  Usage Examples for MIDCOM Transactions

   This section presents some examples that explain how a MIDCOM client
   acting as SNMP manager can use the MIDCOM-MIB module defined in this
   memo.  The purpose of these examples is to explain the steps that are
   required to perform MIDCOM transactions.  For each MIDCOM transaction
   defined in the MIDCOM semantics [RFC5189], a sequence of SNMP
   operations that realizes the transaction is described.

   The examples described below are recommended procedures for MIDCOM
   clients.  Clients may choose to operate differently.

   For example, they may choose not to receive solicited notifications
   on completion of a transaction, but to poll the MIDCOM-MIB instead
   until the transaction is completed.  This can be achieved by
   performing step 2 of the SE transaction (see below) differently.  The
   MIDCOM agent then creates an entry in the snmpNotifyFilterTable such
   that only the midcomUnsolicitedRuleEvent may pass the filter and is
   sent to the MIDCOM client.  In this case, the PER, PRR, and RLC
   transactions require a polling loop wherever in the example below the
   MIDCOM client waits for a notification.







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7.1.  Session Establishment (SE)

   The MIDCOM-MIB realizes most properties of MIDCOM sessions in a very
   static way.  Only the generation of notifications targeted at the
   MIDCOM client is enabled by the client for session establishment.

   1. The MIDCOM client checks the middlebox capabilities by reading
      objects in the midcomCapabilitiesGroup.

   2. The MIDCOM client enables generation of notifications on events
      concerning the policy rules controlled by the client.  If the
      SNMP-NOTIFICATION-MIB is supported as recommended by section 6.3
      of this document, then the agent just has to change the value of a
      object snmpNotifyFilterType in the corresponding entry of the
      snmpNotifyFilterTable from included(1) to excluded(2).

7.2.  Session Termination (ST)

   For terminating a session, the MIDCOM client just disables the
   generation of notifications for this client.

   1. The MIDCOM client disables generation of notifications on events
      concerning the policy rules controlled by the client.  If the
      SNMP-NOTIFICATION-MIB is supported as recommended by section 6.3
      of this document, then the agent just has to change the value of a
      object snmpNotifyFilterType in the corresponding entry of the
      snmpNotifyFilterTable from included(1) to excluded(2).

7.3.  Policy Reserve Rule (PRR)

   This example explains steps that may be performed by a MIDCOM client
   to establish a policy reserve rule.

   1. The MIDCOM client creates a new entry in the midcomRuleTable by
      writing to midcomRuleRowStatus.  The chosen value for index object
      midcomGroupIndex determines the group membership of the created
      rule.  Note that choosing an unused value for midcomGroupIndex
      creates a new entry in the midcomGroupTable.

   2. The MIDCOM client sets the following objects in the new entry of
      the midcomRuleTable to specify all request parameters of the PRR
      transaction:

         - midcomRuleMaxIdleTime
         - midcomRuleInterface
         - midcomRuleTransportProtocol
         - midcomRulePortRange
         - midcomRuleInternalIpVersion



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         - midcomRuleExternalIpVersion
         - midcomRuleInternalIpAddr
         - midcomRuleInternalIpPrefixLength
         - midcomRuleInternalPort
         - midcomRuleLifetime

      Note that several of these parameters have default values that can
      be used.

   3. The MIDCOM client sets the midcomRuleAdminStatus objects in the
      new row of the midcomRuleTable to reserve(1).

   4. The MIDCOM client awaits a midcomSolicitedRuleEvent notification
      concerning the new policy rule in the midcomRuleTable.  Waiting
      for the notification is timed out after a pre-selected maximum
      waiting time.  In case of a timeout while waiting for the
      notification or if the client does not use notifications, the
      MIDCOM client retrieves the status of the midcomRuleEntry by one
      or more SNMP GET operations.

   5. After receiving the midcomSolicitedRuleEvent notification, the
      MIDCOM client checks the lifetime value carried by the
      notification.  If it is greater than 0, the MIDCOM client reads
      all positive reply parameters of the PRR transaction:

         - midcomRuleOutsideIpAddr
         - midcomRuleOutsidePort
         - midcomRuleMaxIdleTime
         - midcomRuleLifetime

      If the lifetime equals 0, then the MIDCOM client reads the
      midcomRuleOperStatus and the midcomRuleError in order to analyze
      the failure reason.

   6. Optionally, after receiving the midcomSolicitedRuleEvent
      notification with a lifetime value greater than 0, the MIDCOM
      client may check the midcomResourceTable for the middlebox
      resources allocated for this policy reserve rule.  Note that PRR
      does not necessarily allocate any middlebox resource visible in
      the NAT-MIB module or in a firewall MIB module, since it does a
      reservation only.  If, however, the PRR overlaps with already
      existing PERs, then the PRR may be related to middlebox resources
      visible in other MIB modules.








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7.4.  Policy Enable Rule (PER) after PRR

   This example explains steps that may be performed by a MIDCOM client
   to establish a policy enable rule after a corresponding policy
   reserve rule was already established.

   1. The MIDCOM client sets the following objects in the row of the
      established PRR in the midcomRuleTable to specify all request
      parameters of the PER transaction:

         - midcomRuleMaxIdleTime
         - midcomRuleExternalIpAddr
         - midcomRuleExternalIpPrefixLength
         - midcomRuleExternalPort
         - midcomRuleFlowDirection

      Note that several of these parameters have default values that can
      be used.

   2. The MIDCOM client sets the midcomRuleAdminStatus objects in the
      row of the established PRR in the midcomRuleTable to enable(1).

   3. The MIDCOM client awaits a midcomSolicitedRuleEvent notification
      concerning the new row in the midcomRuleTable.  Waiting for the
      notification is timed out after a pre-selected maximum waiting
      time.  In case of a timeout while waiting for the notification or
      if the client does not use notifications, the MIDCOM client
      retrieves the status of the midcomRuleEntry by one or more SNMP
      GET operations.

   4. After receiving the midcomSolicitedRuleEvent notification, the
      MIDCOM client checks the lifetime value carried by the
      notification.  If it is greater than 0, the MIDCOM client reads
      all positive reply parameters of the PER transaction:

         - midcomRuleInsideIpAddr
         - midcomRuleInsidePort
         - midcomRuleMaxIdleTime

      If the lifetime equals 0, then the MIDCOM client reads the
      midcomRuleOperStatus and the midcomRuleError in order to analyze
      the failure reason.

   5. Optionally, after receiving the midcomSolicitedRuleEvent
      notification with a lifetime value greater than 0, the MIDCOM
      client may check the midcomResourceTable for the allocated
      middlebox resources for this policy enable rule.




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7.5.  Policy Enable Rule (PER) without Previous PRR

   This example explains steps that may be performed by a MIDCOM client
   to establish a policy enable rule for which no PRR transaction has
   been performed before.

   1. Identical to step 1 for PRR (section 7.3).

   2. Identical to step 2 for PRR (section 7.3).

   3. The MIDCOM client sets the following objects in the new row of the
      midcomRuleTable to specify all request parameters of the PER
      transaction:

         - midcomRuleInterface
         - midcomRuleFlowDirection
         - midcomRuleTransportProtocol
         - midcomRulePortRange
         - midcomRuleInternalIpVersion
         - midcomRuleExternalIpVersion
         - midcomRuleInternalIpAddr
         - midcomRuleInternalIpPrefixLength
         - midcomRuleInternalPort
         - midcomRuleExternalIpAddr
         - midcomRuleExternalIpPrefixLength
         - midcomRuleExternalPort
         - midcomRuleLifetime

      Note that several of these parameters have default values that can
      be used.

   4. The MIDCOM client sets the midcomRuleAdminStatus objects in the
      new row of the midcomRuleTable to enable(1).

   5. Identical to step 4 for PRR (section 7.3).

   6. After receiving the midcomSolicitedRuleEvent notification, the
      MIDCOM client checks the lifetime value carried by the
      notification.  If it is greater than 0, the MIDCOM client reads
      all positive reply parameters of the PRR transaction:

         - midcomRuleInsideIpAddr
         - midcomRuleInsidePort
         - midcomRuleOutsideIpAddr
         - midcomRuleOutsidePort
         - midcomRuleMaxIdleTime





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      If the lifetime equals 0, then the MIDCOM client reads the
      midcomRuleOperStatus and the midcomRuleError in order to analyze
      the failure reason.

   7. Optionally, after receiving the midcomSolicitedRuleEvent
      notification with a lifetime value greater than 0, the MIDCOM
      client may check the midcomResourceTable for the allocated
      middlebox resources for this policy enable rule.

7.6.  Policy Rule Lifetime Change (RLC)

   This example explains steps that may be performed by a MIDCOM client
   to change the lifetime of a policy rule.  Changing the lifetime to 0
   implies terminating the policy rule.

   1. The MIDCOM client issues a SET request for writing the desired
   lifetime to the midcomRuleLifetime object in the corresponding row of
   the midcomRuleTable.  This does not have any effect if the lifetime
   is already expired.

   2. The MIDCOM client awaits a midcomSolicitedRuleEvent notification
   concerning the corresponding row in the midcomRuleTable.  Waiting for
   the notification is timed out after a pre-selected maximum waiting
   time.  In case of a timeout while waiting for the notification or if
   the client does not use notifications, the MIDCOM client retrieves
   the status of the midcomRuleEntry by one or more SNMP GET operations.

   3. After receiving the midcomSolicitedRuleEvent notification MIDCOM
   client checks the lifetime value carried by the notification.

7.7.  Policy Rule List (PRL)

   The SNMP agent can browse the list of policy rules by browsing the
   midcomRuleTable.  For each observed row in this table, the SNMP agent
   should check the midcomRuleOperStatus in order to find out if the row
   contains information about an established policy rule or of a rule
   that is under construction or already terminated.

7.8.  Policy Rule Status (PRS)

   The SNMP agent can retrieve all status information and properties of
   a policy rule by reading the managed objects in the corresponding row
   of the midcomRuleTable.








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7.9.  Asynchronous Policy Rule Event (ARE)

   There are two different triggers for the ARE.  It may be triggered by
   the expiration of a policy rule's lifetime or the expiration of the
   idle time.  But beyond this, the MIDCOM-MIB implementation may
   terminate a policy rule at any time.  In all cases, two steps are
   required for performing this transaction:

   1. The MIDCOM-MIB implementation sends a midcomUnsolicitedRuleEvent
      notification containing a lifetime value of 0 to the MIDCOM client
      owning the rule.

   2. If the midcomRuleStorageTime object in the corresponding row of
      the midcomRuleTable has a value of 0, then the MIDCOM-MIB
      implementation removes the row from the table.  Otherwise, it sets
      in this row the midcomRuleLifetime object to 0 and changes the
      midcomRuleOperStatus object.  If the event was triggered by policy
      lifetime expiration, then the midcomRuleOperStatus is set to
      timedOut(9); otherwise, it is set to terminated(11).

7.10.  Group Lifetime Change (GLC)

   This example explains steps that may be performed by a MIDCOM client
   to change the lifetime of a policy rule group.  Changing the lifetime
   to 0 implies terminating all member policies of the group.

   1. The MIDCOM client issues a SET request for writing the desired
      lifetime to the midcomGroupLifetime object in the corresponding
      row of the midcomGroupTable.

   2. The MIDCOM client waits for a midcomSolicitedGroupEvent
      notification concerning the corresponding row in the
      midcomGroupTable.  Waiting for the notification is timed out after
      a pre-selected maximum waiting time.  In case of a timeout while
      waiting for the notification or if the client does not use
      notifications, the MIDCOM client retrieves the status of the
      midcomGroupEntry by one or more SNMP GET operations.

   3. After receiving the midcomSolicitedRuleEvent notification, the
      MIDCOM client checks the lifetime value carried by the
      notification.

7.11.  Group List (GL)

   The SNMP agent can browse the list of policy rule groups by browsing
   the midcomGroupTable.  For each observed row in this table, the SNMP
   agent should check the midcomGroupLifetime in order to find out if
   the group does contain established policies.



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7.12.  Group Status (GS)

   The SNMP agent can retrieve all member policies of a group by
   browsing the midcomRuleTable using the midcomGroupIndex of the
   particular group.  For retrieving the remaining lifetime of the
   group, the SNMP agent reads the midcomGroupLifetime object in the
   corresponding row of the midcomGroupTable.

8.  Usage Examples for Monitoring Objects

   This section presents some examples that explain how a MIDCOM client
   can use the midcomResourceTable to correlate policy rules with the
   used middlebox resources.  One example is given for middleboxes
   implementing the NAT-MIB and another one is given for firewalls.

8.1.  Monitoring NAT Resources

   When a rule in the midcomRuleTable is executed, it directly impacts
   the middlebox resources.  The midcomResourceTable provides the
   information on the relationships between the MIDCOM-MIB policy rules
   and the middlebox resources used for enforcing these rules.

   A MIDCOM-MIB policy rule will cause the creation or modification of
   up to two NAT bindings and up to two NAT sessions.  Two NAT bindings
   are impacted in the case of a session being subject to twice-NAT.
   Two NAT bindings may also be impacted when midcomRulePortRange is set
   to pair(2) in the policy rule.  In the majority of cases, where
   traditional NAT is implemented, only a single NAT binding may be
   adequate.  Note, however, that this BindId is set to 0 if the
   middlebox is implementing symmetric NAT function.  Two NAT sessions
   are created or modified only when the midcomRulePortRange is set to
   pair(2) in the policy rule.

   When support for the NAT-MIB module is also available at the
   middlebox, the parameters in the combination of the midcomRuleTable
   and the midcomResourceTable for a given rule can be used to index the
   corresponding BIND and NAT session resources effected in the NAT-MIB.
   These parameters are valuable to monitor the impact on the NAT
   module, even when the NAT-MIB module is not implemented at the
   middlebox.

   The impact of MIDCOM rules on the NAT resources is important because
   a MIDCOM rule not only can create BINDs and NAT sessions, but also is
   capable of modifying the NAT objects that already exist.  For
   example, FlowDirection and MaxIdleTime parameters in a MIDCOM rule
   directly affect the TranslationEntity and MaxIdleTime of the
   associated NAT bind object.  Likewise, MaxIdleTime in a MIDCOM rule




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   has a direct impact on the MaxIdleTime of the associated NAT session
   object.  The lifetime parameter in the MIDCOM rule directly impacts
   the lifetime of all the impacted NAT BIND and NAT session objects.

8.2.  Monitoring Firewall Resources

   When a MIDCOM-MIB policy rule is established at a middlebox with
   firewall capabilities, this may lead to the creation of one or more
   new firewall rules.  Note that in general a single firewall rule per
   MIDCOM-MIB policy rule will be sufficient.  For each policy rule, a
   MIDCOM client can explore the corresponding firewall filter rule by
   reading the midcomResourceEntry in the midcomResourceTable that
   corresponds to the midcomRuleEntry describing the rule.  The
   identification of the firewall filter rule is stored in object
   midcomRscFirewallRuleId.  The value of midcomRscFirewallRuleId may
   correspond directly to any firewall filter rule number or to an entry
   in a locally available firewall MIB module.

9.  Definitions

   The following MIB module imports from [RFC2578], [RFC2579],
   [RFC2580], [RFC2863], [RFC3411], [RFC4001], and [RFC4008].

   MIDCOM-MIB DEFINITIONS ::= BEGIN

   IMPORTS
       MODULE-IDENTITY, OBJECT-TYPE,
       NOTIFICATION-TYPE, Unsigned32,
       Counter32, Gauge32, mib-2
           FROM SNMPv2-SMI                  -- RFC 2578

       TEXTUAL-CONVENTION, TruthValue,
       StorageType, RowStatus
           FROM SNMPv2-TC                   -- RFC 2579

       MODULE-COMPLIANCE, OBJECT-GROUP,
       NOTIFICATION-GROUP
           FROM SNMPv2-CONF                 -- RFC 2580

       SnmpAdminString
           FROM SNMP-FRAMEWORK-MIB          -- RFC 3411

       InetAddressType, InetAddress,
       InetPortNumber,
       InetAddressPrefixLength
           FROM INET-ADDRESS-MIB            -- RFC 4001





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       InterfaceIndexOrZero
           FROM IF-MIB                      -- RFC 2863

       NatBindIdOrZero
           FROM NAT-MIB;                    -- RFC 4008

   midcomMIB MODULE-IDENTITY
       LAST-UPDATED "200708091011Z"  -- August 09, 2007
       ORGANIZATION "IETF Middlebox Communication Working Group"
       CONTACT-INFO
          "WG charter:
             http://www.ietf.org/html.charters/midcom-charter.html

           Mailing Lists:
             General Discussion: midcom@ietf.org
             To Subscribe: midcom-request@ietf.org
             In Body: subscribe your_email_address

           Co-editor:
             Juergen Quittek
             NEC Europe Ltd.
             Kurfuersten-Anlage 36
             69115 Heidelberg
             Germany
             Tel: +49 6221 4342-115
             Email: quittek@nw.neclab.eu

           Co-editor:
             Martin Stiemerling
             NEC Europe Ltd.
             Kurfuersten-Anlage 36
             69115 Heidelberg
             Germany
             Tel: +49 6221 4342-113
             Email: stiemerling@nw.neclab.eu

           Co-editor:
             Pyda Srisuresh
             Kazeon Systems, Inc.
             1161 San Antonio Rd.
             Mountain View, CA 94043
             U.S.A.
             Tel: +1 408 836-4773
             Email: srisuresh@yahoo.com"

       DESCRIPTION
           "This MIB module defines a set of basic objects for
            configuring middleboxes, such as firewalls and network



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            address translators, in order to enable communication
            across these devices.

            Managed objects defined in this MIB module are structured
            in three kinds of objects:
              - transaction objects required according to the MIDCOM
                protocol requirements defined in RFC 3304 and according
                to the MIDCOM protocol semantics defined in RFC 3989,
              - configuration objects that can be used for retrieving or
                setting parameters of the implementation of transaction
                objects,
              - optional monitoring objects that provide information
                about used resource and statistics

            The transaction objects are organized in two subtrees:
              - objects modeling MIDCOM policy rules in the
                midcomRuleTable
              - objects modeling MIDCOM policy rule groups in the
                midcomGroupTable

            Note that typically, configuration objects are not intended
            to be written by MIDCOM clients.  In general, write access
            to these objects needs to be restricted more strictly than
            write access to objects in the transaction subtrees.

            Copyright (C) The Internet Society (2008).  This version
            of this MIB module is part of RFC 5190;  see the RFC
            itself for full legal notices."

       REVISION    "200708091011Z"  -- August 09, 2007
       DESCRIPTION "Initial version, published as RFC 5190."
       ::= { mib-2 171 }

   --
   -- main components of this MIB module
   --

   midcomNotifications   OBJECT IDENTIFIER ::= { midcomMIB 0 }
   midcomObjects         OBJECT IDENTIFIER ::= { midcomMIB 1 }
   midcomConformance     OBJECT IDENTIFIER ::= { midcomMIB 2 }

   --  Transaction objects required according to the MIDCOM
   --  protocol requirements defined in RFC 3304 and according to
   --  the MIDCOM protocol semantics defined in RFC 3989
   midcomTransaction     OBJECT IDENTIFIER ::= { midcomObjects 1 }

   --  Configuration objects that can be used for retrieving
   --  middlebox capability information (mandatory) and for



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   --  setting parameters of the implementation of transaction
   --  objects (optional)
   midcomConfig   OBJECT IDENTIFIER ::= { midcomObjects 2 }

   --  Optional monitoring objects that provide information about
   --  used resource and statistics
   midcomMonitoring      OBJECT IDENTIFIER ::= { midcomObjects 3 }

   --
   -- Transaction Objects
   --
   -- Transaction objects are structured according to the MIDCOM
   -- protocol semantics into two groups:
   --   - objects modeling MIDCOM policy rules in the midcomRuleTable
   --   - objects modeling MIDCOM policy rule groups in the
   --     midcomGroupTable

   --
   -- Policy rule subtree
   --
   -- The midcomRuleTable lists policy rules
   -- including policy reserve rules and policy enable rules.
   --

   midcomRuleTable OBJECT-TYPE
       SYNTAX      SEQUENCE OF MidcomRuleEntry
       MAX-ACCESS  not-accessible
       STATUS      current
       DESCRIPTION
           "This table lists policy rules.

            It is indexed by the midcomRuleOwner, the
            midcomGroupIndex, and the midcomRuleIndex.
            This implies that a rule is a member of exactly
            one group and that group membership cannot
            be changed.

            Entries can be deleted by writing to
            midcomGroupLifetime or midcomRuleLifetime
            and potentially also to midcomRuleStorageTime."
       ::= { midcomTransaction 3 }

   midcomRuleEntry OBJECT-TYPE
       SYNTAX      MidcomRuleEntry
       MAX-ACCESS  not-accessible
       STATUS      current
       DESCRIPTION
           "An entry describing a particular MIDCOM policy rule."



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       INDEX { midcomRuleOwner, midcomGroupIndex, midcomRuleIndex }
       ::= { midcomRuleTable 1 }

   MidcomRuleEntry ::= SEQUENCE {
       midcomRuleOwner                   SnmpAdminString,
       midcomRuleIndex                   Unsigned32,
       midcomRuleAdminStatus             INTEGER,
       midcomRuleOperStatus              INTEGER,
       midcomRuleStorageType             StorageType,
       midcomRuleStorageTime             Unsigned32,
       midcomRuleError                   SnmpAdminString,
       midcomRuleInterface               InterfaceIndexOrZero,
       midcomRuleFlowDirection           INTEGER,
       midcomRuleMaxIdleTime             Unsigned32,
       midcomRuleTransportProtocol       Unsigned32,
       midcomRulePortRange               INTEGER,
       midcomRuleInternalIpVersion       InetAddressType,
       midcomRuleExternalIpVersion       InetAddressType,
       midcomRuleInternalIpAddr          InetAddress,
       midcomRuleInternalIpPrefixLength  InetAddressPrefixLength,
       midcomRuleInternalPort            InetPortNumber,
       midcomRuleExternalIpAddr          InetAddress,
       midcomRuleExternalIpPrefixLength  InetAddressPrefixLength,
       midcomRuleExternalPort            InetPortNumber,
       midcomRuleInsideIpAddr            InetAddress,
       midcomRuleInsidePort              InetPortNumber,
       midcomRuleOutsideIpAddr           InetAddress,
       midcomRuleOutsidePort             InetPortNumber,
       midcomRuleLifetime                Unsigned32,
       midcomRuleRowStatus               RowStatus
   }

   midcomRuleOwner OBJECT-TYPE
       SYNTAX      SnmpAdminString (SIZE (0..32))
       MAX-ACCESS  not-accessible
       STATUS      current
       DESCRIPTION
           "The manager who owns this row in the midcomRuleTable.

            This object SHOULD uniquely identify an authenticated
            MIDCOM client.  This object is part of the table index to
            allow for the use of the SNMPv3 View-based Access Control
            Model (VACM, RFC 3415)."
       ::= { midcomRuleEntry 1 }

   midcomRuleIndex OBJECT-TYPE
       SYNTAX      Unsigned32 (1..4294967295)
       MAX-ACCESS  not-accessible



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       STATUS      current
       DESCRIPTION
           "The value of this object must be unique in
            combination with the values of the objects
            midcomRuleOwner and midcomGroupIndex in this row."
       ::= { midcomRuleEntry 3 }

   midcomRuleAdminStatus OBJECT-TYPE
       SYNTAX      INTEGER {
                       reserve(1),
                       enable(2),
                       notSet(3)
                   }
       MAX-ACCESS  read-create
       STATUS      current
       DESCRIPTION
           "The value of this object indicates the desired status of
            the policy rule.  See the definition of midcomRuleOperStatus
            for a description of the values.

            When a midcomRuleEntry is created without explicitly setting
            this object, its value will be notSet(3).

            However, a SET request can only set this object to either
            reserve(1) or enable(2).  Attempts to set this object to
            notSet(3) will always fail with an 'inconsistentValue'
            error.  Note that this error code is SNMP specific.  If the
            MIB module is used with other protocols than SNMP, errors
            with similar semantics specific to those protocols should
            be returned.

            When the midcomRuleAdminStatus object is set, then the
            MIDCOM-MIB implementation will try to read the respective
            relevant objects of the entry and try to achieve the
            corresponding midcomRuleOperStatus.

            Setting midcomRuleAdminStatus to value reserve(1) when
            object midcomRuleOperStatus has a value of reserved(7)
            does not have any effect on the policy rule.
            Setting midcomRuleAdminStatus to value enable(2) when
            object midcomRuleOperStatus has a value of enabled(8)
            does not have any effect on the policy rule.

            Depending on whether the midcomRuleAdminStatus is set to
            reserve(1) or enable(2), several objects must be set in
            advance.  They serve as parameters of the policy rule to be
            established.




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            When object midcomRuleAdminStatus is set to reserve(1),
            then the following objects in the same entry are of
            relevance:
                - midcomRuleInterface
                - midcomRuleTransportProtocol
                - midcomRulePortRange
                - midcomRuleInternalIpVersion
                - midcomRuleExternalIpVersion
                - midcomRuleInternalIpAddr
                - midcomRuleInternalIpPrefixLength
                - midcomRuleInternalPort
                - midcomRuleLifetime

            MIDCOM-MIB implementation may also consider the value
            of object midcomRuleMaxIdleTime when establishing
            a reserve rule.

            When object midcomRuleAdminStatus is set to enable(2),
            then the following objects in the same entry are of
            relevance:
                - midcomRuleInterface
                - midcomRuleFlowDirection
                - midcomRuleMaxIdleTime
                - midcomRuleTransportProtocol
                - midcomRulePortRange
                - midcomRuleInternalIpVersion
                - midcomRuleExternalIpVersion
                - midcomRuleInternalIpAddr
                - midcomRuleInternalIpPrefixLength
                - midcomRuleInternalPort
                - midcomRuleExternalIpAddr
                - midcomRuleExternalIpPrefixLength
                - midcomRuleExternalPort
                - midcomRuleLifetime

            When retrieved, the object returns the last set value.
            If no value has been set, it returns the default value
            notSet(3)."
       DEFVAL { notSet }
       ::= { midcomRuleEntry 4 }

   midcomRuleOperStatus OBJECT-TYPE
       SYNTAX      INTEGER {
                       newEntry(1),
                       setting(2),
                       checkingRequest(3),
                       incorrectRequest(4),
                       processingRequest(5),



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                       requestRejected(6),
                       reserved(7),
                       enabled(8),
                       timedOut(9),
                       terminatedOnRequest(10),
                       terminated(11),
                       genericError(12)
                   }
       MAX-ACCESS  read-only
       STATUS      current
       DESCRIPTION
           "The actual status of the policy rule.  The
            midcomRuleOperStatus object may have the following values:

            - newEntry(1) indicates that the entry in the
              midcomRuleTable was created, but not modified yet.
              Such an entry needs to be filled with values specifying
              a request first.

            - setting(2) indicates that the entry has been already
              modified after generating it, but no request was made
              yet.

            - checkingRequest(3) indicates that midcomRuleAdminStatus
              has recently been set and that the MIDCOM-MIB
              implementation is currently checking the parameters of
              the request.  This is a transient state.  The value of
              this object will change to either incorrectRequest(4)
              or processingRequest(5) without any external
              interaction.  A MIDCOM-MIB implementation MAY return
              this value while checking request parameters.

            - incorrectRequest(4) indicates that checking a request
              resulted in detecting an incorrect value in one of the
              objects containing request parameters.  The failure
              reason is indicated by the value of midcomRuleError.

            - processingRequest(5) indicates that
              midcomRuleAdminStatus has recently been set and that
              the MIDCOM-MIB implementation is currently processing
              the request and trying to configure the middlebox
              accordingly.  This is a transient state.  The value of
              this object will change to either requestRejected(6),
              reserved(7), or enabled(8) without any external
              interaction.  A MIDCOM-MIB implementation MAY return
              this value while processing a request.

            - requestRejected(6) indicates that a request to establish



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              a policy rule specified by the entry was rejected.  The
              reason for rejection is indicated by the value of
              midcomRuleError.

            - reserved(7) indicates that the entry describes an
              established policy reserve rule.
              These values of MidcomRuleEntry are meaningful
              for a reserved policy rule:
                  - midcomRuleMaxIdleTime
                  - midcomRuleInterface
                  - midcomRuleTransportProtocol
                  - midcomRulePortRange
                  - midcomRuleInternalIpVersion
                  - midcomRuleExternalIpVersion
                  - midcomRuleInternalIpAddr
                  - midcomRuleInternalIpPrefixLength
                  - midcomRuleInternalPort
                  - midcomRuleOutsideIpAddr
                  - midcomRuleOutsidePort
                  - midcomRuleLifetime

            - enabled(8) indicates that the entry describes an
              established policy enable rule.
              These values of MidcomRuleEntry are meaningful
              for an enabled policy rule:

                  - midcomRuleFlowDirection
                  - midcomRuleInterface
                  - midcomRuleMaxIdleTime
                  - midcomRuleTransportProtocol
                  - midcomRulePortRange
                  - midcomRuleInternalIpVersion
                  - midcomRuleExternalIpVersion
                  - midcomRuleInternalIpAddr
                  - midcomRuleInternalIpPrefixLength
                  - midcomRuleInternalPort
                  - midcomRuleExternalIpAddr
                  - midcomRuleExternalIpPrefixLength
                  - midcomRuleExternalPort
                  - midcomRuleInsideIpAddr
                  - midcomRuleInsidePort
                  - midcomRuleOutsideIpAddr
                  - midcomRuleOutsidePort
                  - midcomRuleLifetime

            - timedOut(9) indicates that the lifetime of a previously
              established policy rule has expired and that the policy
              rule is terminated for this reason.



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            - terminatedOnRequest(10) indicates that a previously
              established policy rule was terminated by an SNMP
              manager setting the midcomRuleLifetime to 0 or
              setting midcomGroupLifetime to 0.

            - terminated(11) indicates that a previously established
              policy rule was terminated by the MIDCOM-MIB
              implementation for a reason other than lifetime
              expiration or an explicit request from a MIDCOM client.

            - genericError(12) indicates that the policy rule
              specified by the entry is not established due to
              an error condition not listed above.

            The states timedOut(9), terminatedOnRequest(10), and
            terminated(11) are referred to as termination states.

            The states incorrectRequest(4), requestRejected(6),
            and genericError(12) are referred to as error states.

            The checkingRequest(3) and processingRequest(5)
            states are transient states, which will lead to either
            one of the error states or the reserved(7) state or the
            enabled(8) state.  MIDCOM-MIB implementations MAY return
            these values when checking or processing requests."
       DEFVAL { newEntry }
       ::= { midcomRuleEntry 5 }

   midcomRuleStorageType OBJECT-TYPE
       SYNTAX      StorageType
       MAX-ACCESS  read-create
       STATUS      current
       DESCRIPTION
           "When retrieved, this object returns the storage
            type of the policy rule.  Writing to this object can
            change the storage type of the particular row from
            volatile(2) to nonVolatile(3) or vice versa.

            Attempts to set this object to permanent will always
            fail with an 'inconsistentValue' error.  Note that this
            error code is SNMP specific.  If the MIB module is used
            with other protocols than SNMP, errors with similar
            semantics specific to those protocols should be
            returned.

            If midcomRuleStorageType has the value permanent(4),
            then all objects in this row whose MAX-ACCESS value
            is read-create must be read-only."



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       DEFVAL { volatile }
       ::= { midcomRuleEntry 6 }

   midcomRuleStorageTime OBJECT-TYPE
       SYNTAX      Unsigned32
       UNITS       "seconds"
       MAX-ACCESS  read-create
       STATUS      current
       DESCRIPTION
           "The value of this object specifies how long this row
            can exist in the midcomRuleTable after the
            midcomRuleOperStatus switched to a termination state or
            to an error state.  This object returns the remaining
            time that the row may exist before it is aged out.

            After expiration or termination of the context, the value
            of this object ticks backwards.  The entry in the
            midcomRuleTable is destroyed when the value reaches 0.

            The value of this object may be set in order to increase
            or reduce the remaining time that the row may exist.
            Setting the value to 0 will destroy this entry as soon as
            the midcomRuleOperStatus switched to a termination state
            or to an error state.

            Note that there is no guarantee that the row is stored as
            long as this object indicates.  At any time, the MIDCOM-
            MIB implementation may decide to remove a row describing
            a terminated policy rule before the storage time of the
            corresponding row in the midcomRuleTable reaches the
            value of 0.  In this case, the information stored in this
            row is not available anymore.

            If object midcomRuleStorageType indicates that the policy
            rule has the storage type permanent(4), then this object has
            a constant value of 4294967295."
       DEFVAL { 0 }
       ::= { midcomRuleEntry 7 }

   midcomRuleError OBJECT-TYPE
       SYNTAX      SnmpAdminString
       MAX-ACCESS  read-only
       STATUS      current
       DESCRIPTION
           "This object contains a descriptive error message if
            the transition into the operational status reserved(7)
            or enabled(8) failed.  Implementations must reset the
            error message to a zero-length string when a new



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            attempt to change the policy rule status to reserved(7)
            or enabled(8) is started.

            RECOMMENDED values to be returned in particular cases
            include
              - 'lack of IP addresses'
              - 'lack of port numbers'
              - 'lack of resources'
              - 'specified NAT interface does not exist'
              - 'specified NAT interface does not support NAT'
              - 'conflict with already existing policy rule'
              - 'no internal IP wildcarding allowed'
              - 'no external IP wildcarding allowed'

            The semantics of these error messages and the corresponding
            behavior of the MIDCOM-MIB implementation are specified
            in sections 2.3.9 and 2.3.10 of RFC 3989."
       REFERENCE
           "RFC 3989, sections 2.3.9 and 2.3.10"
       DEFVAL { ''H }
       ::= { midcomRuleEntry 8 }

   midcomRuleInterface OBJECT-TYPE
       SYNTAX      InterfaceIndexOrZero
       MAX-ACCESS  read-create
       STATUS      current
       DESCRIPTION
           "This object indicates the IP interface for which
            enforcement of a policy rule is requested or performed,
            respectively.

            The interface is identified by its index in the ifTable
            (see IF-MIB in RFC 2863).  If the object has a value of 0,
            then no particular interface is indicated.

            This object is used as input to a request for establishing
            a policy rule as well as for indicating the properties of
            an established policy rule.

            If object midcomRuleOperStatus of the same entry has the
            value newEntry(1) or setting(2), then this object can be
            written by a manager in order to request its preference
            concerning the interface at which it requests NAT service.
            The default value of 0 indicates that the manager does not
            have a preferred interface or does not have sufficient
            topology information for specifying one.  Writing to this
            object in any state other than newEntry(1) or setting(2)
            will always fail with an 'inconsistentValue' error.



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            Note that this error code is SNMP specific.  If the MIB
            module is used with other protocols than SNMP, errors with
            similar semantics specific to those protocols should be
            returned.

            If object midcomRuleOperStatus of the same entry has the
            value reserved(7) or enabled(8), then this object indicates
            the interface at which NAT service for this rule is
            performed.  If NAT service is not required for enforcing
            the policy rule, then the value of this object is 0.  Also,
            if the MIDCOM-MIB implementation cannot indicate an
            interface, because it does not have this information or
            because NAT service is not offered at a particular single
            interface, then the value of the object is 0.

            Note that the index of a particular interface in the
            ifTable may change after a re-initialization of the
            middlebox, for example, after adding another interface to
            it.  In such a case, the value of this object may change,
            but the interface referred to by the MIDCOM-MIB MUST still
            be the same.  If, after a re-initialization of the
            middlebox, the interface referred to before
            re-initialization cannot be uniquely mapped anymore to a
            particular entry in the ifTable, then the value of object
            midcomRuleOperStatus of the same entry MUST be changed to
            terminated(11).

            If object midcomRuleOperStatus of the same entry has a
            value other than newEntry(1), setting(2), reserved(7), or
            enabled(8), then the value of this object is irrelevant."
       DEFVAL { 0 }
       ::= { midcomRuleEntry 9 }

   midcomRuleFlowDirection OBJECT-TYPE
       SYNTAX      INTEGER {
                       inbound(1),
                       outbound(2),
                       biDirectional(3)
                   }
       MAX-ACCESS  read-create
       STATUS      current
       DESCRIPTION
           "This parameter specifies the direction of enabled
            communication, either inbound(1), outbound(2), or
            biDirectional(3).

            The semantics of this object depends on the protocol
            the rule relates to.  If the rule is independent of



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            the transport protocol (midcomRuleTransportProtocol
            has a value of 0) or if the transport protocol is UDP,
            then the value of midcomRuleFlowDirection indicates
            the direction of packets traversing the middlebox.

            In this case, value inbound(1) indicates that packets
            are traversing from outside to inside, value outbound(2)
            indicates that packets are traversing from inside to
            outside.  For both values, inbound(1) and outbound(2)
            packets can traverse the middlebox only unidirectional.
            A bidirectional flow is indicated by value
            biDirectional(3).

            If the transport protocol is TCP, the packet flow is
            always bidirectional, but the value of
            midcomRuleFlowDirection indicates that:

              - inbound(1): bidirectional TCP packet flow.
                First packet, with TCP SYN flag set, must arrive
                at an outside interface of the middlebox.

              - outbound(2): bidirectional TCP packet flow.
                First packet, with TCP SYN flag set, must arrive
                at an inside interface of the middlebox.

              - biDirectional(3): bidirectional TCP packet flow.
                First packet, with TCP SYN flag set, may arrive
                at an inside or an outside interface of the middlebox.

            This object is used as input to a request for
            establishing a policy enable rule as well as for
            indicating the properties of an established policy rule.

            If object midcomRuleOperStatus of the same entry has a
            value of either newEntry(1), setting(2), or reserved(7),
            then this object can be written by a manager in order to
            specify a requested direction to be enabled by a policy
            rule.  Writing to this object in any state other than
            newEntry(1), setting(2), or reserved(7) will always fail
            with an 'inconsistentValue' error.

            Note that this error code is SNMP specific.  If the MIB
            module is used with other protocols than SNMP, errors with
            similar semantics specific to those protocols should be
            returned.

            If object midcomRuleOperStatus of the same entry has the
            value enabled(8), then this object indicates the enabled



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            flow direction.

            If object midcomRuleOperStatus of the same entry has a
            value other than newEntry(1), setting(2), reserved(7), or
            enabled(8), then the value of this object is irrelevant."
       DEFVAL { outbound }
       ::= { midcomRuleEntry 10 }

   midcomRuleMaxIdleTime OBJECT-TYPE
       SYNTAX      Unsigned32
       UNITS       "seconds"
       MAX-ACCESS  read-create
       STATUS      current
       DESCRIPTION
           "Maximum idle time of the policy rule in seconds.

            If no packet to which the policy rule applies passes the
            middlebox for the specified midcomRuleMaxIdleTime, then
            the policy rule enters the termination state timedOut(9).

            A value of 0 indicates that the policy does not require
            an individual idle time and that instead, a default idle
            time chosen by the middlebox is used.

            A value of 4294967295 ( = 2^32 - 1 ) indicates that the
            policy does not time out if it is idle.

            This object is used as input to a request for
            establishing a policy enable rule as well as for
            indicating the properties of an established policy rule.

            If object midcomRuleOperStatus of the same entry has a
            value of either newEntry(1), setting(2), or reserved(7),
            then this object can be written by a manager in order to
            specify a maximum idle time for the policy rule to be
            requested.  Writing to this object in any state others
            than newEntry(1), setting(2), or reserved(7) will always
            fail with an 'inconsistentValue' error.

            Note that this error code is SNMP specific.  If the MIB
            module is used with other protocols than SNMP, errors with
            similar semantics specific to those protocols should be
            returned.

            If object midcomRuleOperStatus of the same entry has the
            value enabled(8), then this object indicates the maximum
            idle time of the policy rule.  Note that even if a maximum
            idle time greater than zero was requested, the middlebox



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            may not be able to support maximum idle times and set the
            value of this object to zero when entering state
            enabled(8).

            If object midcomRuleOperStatus of the same entry has a
            value other than newEntry(1), setting(2), reserved(7), or
            enabled(8), then the value of this object is irrelevant."
       DEFVAL { 0 }
       ::= { midcomRuleEntry 11 }

   midcomRuleTransportProtocol OBJECT-TYPE
       SYNTAX      Unsigned32 (0..255)
       MAX-ACCESS  read-create
       STATUS      current
       DESCRIPTION
           "The transport protocol.

            Valid values for midcomRuleTransportProtocol
            other than zero are defined at:
            http://www.iana.org/assignments/protocol-numbers

            This object is used as input to a request for establishing
            a policy rule as well as for indicating the properties of
            an established policy rule.

            If object midcomRuleOperStatus of the same entry has a
            value of either newEntry(1) or setting(2), then this
            object can be written by a manager in order to specify a
            requested transport protocol.  If translation of an IP
            address only is requested, then this object must have the
            default value 0.  Writing to this object in any state
            other than newEntry(1) or setting(2) will always fail
            with an 'inconsistentValue' error.

            Note that this error code is SNMP specific.  If the MIB
            module is used with other protocols than SNMP, errors with
            similar semantics specific to those protocols should be
            returned.

            If object midcomRuleOperStatus of the same entry has the
            value reserved(7) or enabled(8), then this object
            indicates which transport protocol is enforced by this
            policy rule.  A value of 0 indicates a rule acting on IP
            addresses only.

            If object midcomRuleOperStatus of the same entry has a
            value other than newEntry(1), setting(2), reserved(7), or
            enabled(8), then the value of this object is irrelevant."



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       DEFVAL { 0 }
       ::= { midcomRuleEntry 12 }

   midcomRulePortRange OBJECT-TYPE
       SYNTAX      INTEGER {
                       single(1),
                       pair(2)
                   }
       MAX-ACCESS  read-create
       STATUS      current
       DESCRIPTION
           "The range of port numbers.

            This object is used as input to a request for establishing
            a policy rule as well as for indicating the properties of
            an established policy rule.  It is relevant to the
            operation of the MIDCOM-MIB implementation only if the
            value of object midcomTransportProtocol in the same entry
            has a value other than 0.

            If object midcomRuleOperStatus of the same entry has the
            value newEntry(1) or setting(2), then this object can be
            written by a manager in order to specify the requested
            size of the port range.  With single(1) just a single
            port number is requested, with pair(2) a consecutive pair
            of port numbers is requested with the lower number being
            even.  Requesting a consecutive pair of port numbers may
            be used by RTP [RFC3550] and may even be required to
            support older RTP applications.

            Writing to this object in any state other than
            newEntry(1), setting(2) or reserved(7) will always fail
            with an 'inconsistentValue' error.

            Note that this error code is SNMP specific.  If the MIB
            module is used with other protocols than SNMP, errors with
            similar semantics specific to those protocols should be
            returned.

            If object midcomRuleOperStatus of the same entry has a
            value of either reserved(7) or enabled(8), then this
            object will have the value that it had before the
            transition to this state.

            If object midcomRuleOperStatus of the same entry has a
            value other than newEntry(1), setting(2), reserved(7), or
            enabled(8), then the value of this object is irrelevant."
       DEFVAL { single }



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       ::= { midcomRuleEntry 13}

   midcomRuleInternalIpVersion OBJECT-TYPE
       SYNTAX      InetAddressType
       MAX-ACCESS  read-create
       STATUS      current
       DESCRIPTION
           "IP version of the internal address (A0) and the inside
            address (A1).  Allowed values are ipv4(1), ipv6(2),
            ipv4z(3), and ipv6z(4).

            This object is used as input to a request for establishing
            a policy rule as well as for indicating the properties of
            an established policy rule.

            If object midcomRuleOperStatus of the same entry has the
            value newEntry(1) or setting(2), then this object can be
            written by a manager in order to specify the IP version
            required at the inside of the middlebox.  Writing to this
            object in any state other than newEntry(1) or setting(2)
            will always fail with an 'inconsistentValue' error.

            Note that this error code is SNMP specific.  If the MIB
            module is used with other protocols than SNMP, errors with
            similar semantics specific to those protocols should be
            returned.

            If object midcomRuleOperStatus of the same entry has the
            value reserved(7) or enabled(8), then this object
            indicates the internal/inside IP version.

            If object midcomRuleOperStatus of the same entry has a
            value other than newEntry(1), setting(2), reserved(7), or
            enabled(8), then the value of this object is irrelevant."
       DEFVAL { ipv4 }
       ::= { midcomRuleEntry 14 }

   midcomRuleExternalIpVersion OBJECT-TYPE
       SYNTAX      InetAddressType
       MAX-ACCESS  read-create
       STATUS      current
       DESCRIPTION
           "IP version of the external address (A3) and the outside
            address (A2).  Allowed values are ipv4(1) and ipv6(2).

            This object is used as input to a request for establishing
            a policy rule as well as for indicating the properties of
            an established policy rule.



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            If object midcomRuleOperStatus of the same entry has the
            value newEntry(1) or setting(2), then this object can be
            written by a manager in order to specify the IP version
            required at the outside of the middlebox.  Writing to
            this object in any state other than newEntry(1) or
            setting(2) will always fail with an 'inconsistentValue'
            error.
            Note that this error code is SNMP specific.  If the MIB
            module is used with other protocols than SNMP, errors with
            similar semantics specific to those protocols should be
            returned.

            If object midcomRuleOperStatus of the same entry has the
            value reserved(7) or enabled(8), then this object
            indicates the external/outside IP version.

            If object midcomRuleOperStatus of the same entry has a
            value other than newEntry(1), setting(2), reserved(7) or
            enabled(8), then the value of this object is irrelevant."
       DEFVAL { ipv4 }
       ::= { midcomRuleEntry 15 }

   midcomRuleInternalIpAddr OBJECT-TYPE
       SYNTAX      InetAddress
       MAX-ACCESS  read-create
       STATUS      current
       DESCRIPTION
           "The internal IP address (A0).

            This object is used as input to a request for establishing
            a policy rule as well as for indicating the properties of
            an established policy rule.

            If object midcomRuleOperStatus of the same entry has the
            value newEntry(1) or setting(2), then this object can be
            written by a manager in order to specify the internal IP
            address for which a reserve policy rule or a enable policy
            rule is requested to be established.  Writing to this
            object in any state other than newEntry(1) or setting(2)
            will always fail with an 'inconsistentValue' error.
            Note that this error code is SNMP specific.  If the MIB
            module is used with other protocols than SNMP, errors with
            similar semantics specific to those protocols should be
            returned.

            If object midcomRuleOperStatus of the same entry has the
            value reserved(7) or enabled(8), then this object will
            have the value which it had before the transition to this



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            state.

            If object midcomRuleOperStatus of the same entry has a
            value other than newEntry(1), setting(2), reserved(7) or
            enabled(8), then the value of this object is irrelevant."
       ::= { midcomRuleEntry 16 }

   midcomRuleInternalIpPrefixLength OBJECT-TYPE
       SYNTAX      InetAddressPrefixLength
       MAX-ACCESS  read-create
       STATUS      current
       DESCRIPTION
           "The prefix length of the internal IP address used for
            wildcarding.  A value of 0 indicates a full wildcard;
            in this case, the value of midcomRuleInternalIpAddr is
            irrelevant.  If midcomRuleInternalIpVersion has a value
            of ipv4(1), then a value > 31 indicates no wildcarding
            at all.  If midcomRuleInternalIpVersion has a value
            of ipv4(2), then a value > 127 indicates no wildcarding
            at all.  A MIDCOM-MIB implementation that does not
            support IP address wildcarding MUST implement this object
            as read-only with a value of 128.  A MIDCOM that does
            not support wildcarding based on prefix length MAY
            restrict allowed values for this object to 0 and 128.

            This object is used as input to a request for establishing
            a policy rule as well as for indicating the properties of
            an established policy rule.

            If object midcomRuleOperStatus of the same entry has the
            value newEntry(1) or setting(2), then this object can be
            written by a manager in order to specify the prefix length
            of the internal IP address for which a reserve policy rule
            or an enable policy rule is requested to be established.
            Writing to this object in any state other than newEntry(1)
            or setting(2) will always fail with an 'inconsistentValue'
            error.

            Note that this error code is SNMP specific.  If the MIB
            module is used with other protocols than SNMP, errors with
            similar semantics specific to those protocols should be
            returned.

            If object midcomRuleOperStatus of the same entry has the
            value reserved(7) or enabled(8), then this object will
            have the value which it had before the transition to this
            state.




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            If object midcomRuleOperStatus of the same entry has a
            value other than newEntry(1), setting(2), reserved(7), or
            enabled(8), then the value of this object is irrelevant."
       DEFVAL { 128 }
       ::= { midcomRuleEntry 17 }

   midcomRuleInternalPort OBJECT-TYPE
       SYNTAX      InetPortNumber
       MAX-ACCESS  read-create
       STATUS      current
       DESCRIPTION
           "The internal port number.  A value of 0 is a wildcard.

            This object is used as input to a request for establishing
            a policy rule as well as for indicating the properties of
            an established policy rule.  It is relevant to the
            operation of the MIDCOM-MIB implementation only if the
            value of object midcomTransportProtocol in the same entry
            has a value other than 0.

            If object midcomRuleOperStatus of the same entry has the
            value newEntry(1) or setting(2), then this object can be
            written by a manager in order to specify the internal port
            number for which a reserve policy rule or an enable policy
            rule is requested to be established.  Writing to this
            object in any state other than newEntry(1) or setting(2)
            will always fail with an 'inconsistentValue' error.

            Note that this error code is SNMP specific.  If the MIB
            module is used with other protocols than SNMP, errors with
            similar semantics specific to those protocols should be
            returned.

            If object midcomRuleOperStatus of the same entry has the
            value reserved(7) or enabled(8), then this object will
            have the value that it had before the transition to this
            state.

            If object midcomRuleOperStatus of the same entry has a
            value other than newEntry(1), setting(2), reserved(7), or
            enabled(8), then the value of this object is irrelevant."
       DEFVAL { 0 }
       ::= { midcomRuleEntry 18 }

   midcomRuleExternalIpAddr OBJECT-TYPE
       SYNTAX      InetAddress
       MAX-ACCESS  read-create
       STATUS      current



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       DESCRIPTION
           "The external IP address (A3).

            This object is used as input to a request for establishing
            a policy rule as well as for indicating the properties of
            an established policy rule.

            If object midcomRuleOperStatus of the same entry has the
            value newEntry(1), setting(2), or reserved(7), then this
            object can be written by a manager in order to specify the
            external IP address for which an enable policy rule is
            requested to be established.  Writing to this object in
            any state other than newEntry(1), setting(2), or reserved(7)
            will always fail with an 'inconsistentValue' error.

            Note that this error code is SNMP specific.  If the MIB
            module is used with other protocols than SNMP, errors with
            similar semantics specific to those protocols should be
            returned.

            If object midcomRuleOperStatus of the same entry has the
            value enabled(8), then this object will have the value
            that it had before the transition to this state.

            If object midcomRuleOperStatus of the same entry has a
            value other than newEntry(1), setting(2), reserved(7), or
            enabled(8), then the value of this object is irrelevant."
       ::= { midcomRuleEntry 19 }

   midcomRuleExternalIpPrefixLength OBJECT-TYPE
       SYNTAX      InetAddressPrefixLength
       MAX-ACCESS  read-create
       STATUS      current
       DESCRIPTION
           "The prefix length of the external IP address used for
            wildcarding.  A value of 0 indicates a full wildcard;
            in this case, the value of midcomRuleExternalIpAddr is
            irrelevant.  If midcomRuleExternalIpVersion has a value
            of ipv4(1), then a value > 31 indicates no wildcarding
            at all.  If midcomRuleExternalIpVersion has a value
            of ipv4(2), then a value > 127 indicates no wildcarding
            at all.  A MIDCOM-MIB implementation that does not
            support IP address wildcarding MUST implement this object
            as read-only with a value of 128.  A MIDCOM that does
            not support wildcarding based on prefix length MAY
            restrict allowed values for this object to 0 and 128.

            This object is used as input to a request for establishing



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            a policy rule as well as for indicating the properties of
            an established policy rule.

            If object midcomRuleOperStatus of the same entry has the
            value newEntry(1), setting(2), or reserved(7), then this
            object can be written by a manager in order to specify the
            prefix length of the external IP address for which an
            enable policy rule is requested to be established.
            Writing to this object in any state other than
            newEntry(1), setting(2), or reserved(7) will always fail
            with an 'inconsistentValue' error.

            Note that this error code is SNMP specific.  If the MIB
            module is used with other protocols than SNMP, errors with
            similar semantics specific to those protocols should be
            returned.

            If object midcomRuleOperStatus of the same entry has the
            value enabled(8), then this object will have the value
            that it had before the transition to this state.

            If object midcomRuleOperStatus of the same entry has a
            value other than newEntry(1), setting(2), reserved(7), or
            enabled(8), then the value of this object is irrelevant."
       DEFVAL { 128 }
       ::= { midcomRuleEntry 20 }

   midcomRuleExternalPort OBJECT-TYPE
       SYNTAX      InetPortNumber
       MAX-ACCESS  read-create
       STATUS      current
       DESCRIPTION
           "The external port number.  A value of 0 is a wildcard.

            This object is used as input to a request for establishing
            a policy rule as well as for indicating the properties of
            an established policy rule.  It is relevant to the
            operation of the MIDCOM-MIB implementation only if the
            value of object midcomTransportProtocol in the same entry
            has a value other than 0.

            If object midcomRuleOperStatus of the same entry has the
            value newEntry(1), setting(2) or reserved(7), then this
            object can be written by a manager in order to specify the
            external port number for which an enable policy rule is
            requested to be established.  Writing to this object in
            any state other than newEntry(1), setting(2) or reserved(7)
            will always fail with an 'inconsistentValue' error.



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            Note that this error code is SNMP specific.  If the MIB
            module is used with other protocols than SNMP, errors with
            similar semantics specific to those protocols should be
            returned.

            If object midcomRuleOperStatus of the same entry has the
            value enabled(8), then this object will have the value
            which it had before the transition to this state.

            If object midcomRuleOperStatus of the same entry has a
            value other than newEntry(1), setting(2), reserved(7) or
            enabled(8), then the value of this object is irrelevant."
       DEFVAL { 0 }
       ::= { midcomRuleEntry 21 }

   midcomRuleInsideIpAddr OBJECT-TYPE
       SYNTAX      InetAddress
       MAX-ACCESS  read-only
       STATUS      current
       DESCRIPTION
           "The inside IP address at the middlebox (A1).

            The value of this object is relevant only if
            object midcomRuleOperStatus of the same entry has
            a value of either reserved(7) or enabled(8)."
       ::= { midcomRuleEntry 22 }

   midcomRuleInsidePort OBJECT-TYPE
       SYNTAX      InetPortNumber
       MAX-ACCESS  read-only
       STATUS      current
       DESCRIPTION
           "The inside port number at the middlebox.
            A value of 0 is a wildcard.

            The value of this object is relevant only if
            object midcomRuleOperStatus of the same entry has
            a value of either reserved(7) or enabled(8)."
       ::= { midcomRuleEntry 23 }

   midcomRuleOutsideIpAddr OBJECT-TYPE
       SYNTAX      InetAddress
       MAX-ACCESS  read-only
       STATUS      current
       DESCRIPTION
           "The outside IP address at the middlebox (A2).

            The value of this object is relevant only if



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            object midcomRuleOperStatus of the same entry has
            a value of either reserved(7) or enabled(8)."
       ::= { midcomRuleEntry 24 }

   midcomRuleOutsidePort OBJECT-TYPE
       SYNTAX      InetPortNumber
       MAX-ACCESS  read-only
       STATUS      current
       DESCRIPTION
           "The outside port number at the middlebox.
            A value of 0 is a wildcard.

            The value of this object is relevant only if
            object midcomRuleOperStatus of the same entry has
            a value of either reserved(7) or enabled(8)."
       ::= { midcomRuleEntry 25 }

   midcomRuleLifetime OBJECT-TYPE
       SYNTAX      Unsigned32
       UNITS       "seconds"
       MAX-ACCESS  read-create
       STATUS      current
       DESCRIPTION
           "The remaining lifetime in seconds of this policy rule.

            Lifetime of a policy rule starts when object
            midcomRuleOperStatus in the same entry enters either
            state reserved(7) or state enabled(8).

            This object is used as input to a request for establishing
            a policy rule as well as for indicating the properties of
            an established policy rule.

            If object midcomRuleOperStatus of the same entry has a
            value of either newEntry(1) or setting(2), then this
            object can be written by a manager in order to specify
            the requested lifetime of a policy rule to be established.

            If object midcomRuleOperStatus of the same entry has a
            value of either reserved(7) or enabled(8), then this
            object indicates the (continuously decreasing) remaining
            lifetime of the established policy rule.  Note that when
            entering state reserved(7) or enabled(8), the MIDCOM-MIB
            implementation can choose a lifetime shorter than the one
            requested.

            Unlike other parameters of the policy rule, this parameter
            can still be written in state reserved(7) and enabled(8).



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            Writing to this object is processed by the MIDCOM-MIB
            implementation by choosing a lifetime value that is
            greater than 0 and less than or equal to the minimum of
            the requested value and the value specified by object
            midcomConfigMaxLifetime:

             0 <= lt_granted <= MINIMUM(lt_requested, lt_maximum)

            where:
               - lt_granted is the actually granted lifetime by the
                 MIDCOM-MIB implementation
               - lt_requested is the requested lifetime of the MIDCOM
                 client
               - lt_maximum is the value of object
                 midcomConfigMaxLifetime

            SNMP SET requests to this object may be rejected or the
            value of the object after an accepted SET operation may be
            less than the value that was contained in the SNMP SET
            request.

            Successfully writing a value of 0 terminates the policy
            rule.  Note that after a policy rule is terminated, still
            the entry will exist as long as indicated by the value of
            midcomRuleStorageTime.

            Writing to this object in any state other than
            newEntry(1), setting(2), reserved(7), or enabled(7)
            will always fail with an 'inconsistentValue' error.

            Note that this error code is SNMP specific.  If the MIB
            module is used with other protocols than SNMP, errors with
            similar semantics specific to those protocols should be
            returned.

            If object midcomRuleOperStatus of the same entry has a
            value other than newEntry(1), setting(2), reserved(7), or
            enabled(8), then the value of this object is irrelevant."
       DEFVAL { 180 }
       ::= { midcomRuleEntry 26 }

   midcomRuleRowStatus OBJECT-TYPE
       SYNTAX      RowStatus
       MAX-ACCESS  read-create
       STATUS      current
       DESCRIPTION
           "A control that allows entries to be added and removed from
            this table.



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            Entries can also be removed from this table by setting
            objects midcomRuleLifetime and midcomRuleStorageTime of
            an entry to 0.

            Attempts to set a row notInService(2) where the value
            of the midcomRuleStorageType object is permanent(4) or
            readOnly(5) will result in an 'notWritable' error.

            Note that this error code is SNMP specific.  If the MIB
            module is used with other protocols than SNMP, errors with
            similar semantics specific to those protocols should be
            returned.

            The value of this object has no effect on whether other
            objects in this conceptual row can be modified."
       ::= { midcomRuleEntry 27 }

   --
   -- Policy rule group subtree
   --
   -- The midcomGroupTable lists all current policy rule groups.
   --

   midcomGroupTable OBJECT-TYPE
       SYNTAX      SEQUENCE OF MidcomGroupEntry
       MAX-ACCESS  not-accessible
       STATUS      current
       DESCRIPTION
           "This table lists all current policy rule groups.

            Entries in this table are created or removed
            implicitly when entries in the midcomRuleTable are
            created or removed, respectively.  A group entry
            in this table only exists as long as there are
            member rules of this group in the midcomRuleTable.

            The table serves for listing the existing groups and
            their remaining lifetimes and for changing lifetimes
            of groups and implicitly of all group members.
            Groups and all their member policy rules can only be
            deleted by deleting all member policies in the
            midcomRuleTable.

            Setting midcomGroupLifetime will result in setting
            the lifetime of all policy members to the same value."
       ::= { midcomTransaction 4 }

   midcomGroupEntry OBJECT-TYPE



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       SYNTAX      MidcomGroupEntry
       MAX-ACCESS  not-accessible
       STATUS      current
       DESCRIPTION
           "An entry describing properties of a particular
            MIDCOM policy rule group."
       INDEX { midcomRuleOwner, midcomGroupIndex }
       ::= { midcomGroupTable 1 }

   MidcomGroupEntry ::= SEQUENCE {
       midcomGroupIndex      Unsigned32,
       midcomGroupLifetime   Unsigned32
   }

   midcomGroupIndex OBJECT-TYPE
       SYNTAX      Unsigned32 (1..4294967295)
       MAX-ACCESS  not-accessible
       STATUS      current
       DESCRIPTION
           "The index of this group for the midcomRuleOwner.
            A group is identified by the combination of
            midcomRuleOwner and midcomGroupIndex.

            The value of this index must be unique per
            midcomRuleOwner."
       ::= { midcomGroupEntry 2 }

   midcomGroupLifetime OBJECT-TYPE
       SYNTAX      Unsigned32
       UNITS       "seconds"
       MAX-ACCESS  read-write
       STATUS      current
       DESCRIPTION
           "When retrieved, this object delivers the maximum
            lifetime in seconds of all member rules of this group,
            i.e., of all rows in the midcomRuleTable that have the
            same values for midcomRuleOwner and midcomGroupIndex.

            Successfully writing to this object modifies the
            lifetime of all member policies.  Successfully
            writing a value of 0 terminates all member policies
            and implicitly deletes the group as soon as all member
            entries are removed from the midcomRuleTable.

            Note that after a group's lifetime is expired or is
            set to 0, still the corresponding entry in the
            midcomGroupTable will exist as long as terminated
            member policy rules are stored as entries in the



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            midcomRuleTable.

            Writing to this object is processed by the MIDCOM-MIB
            implementation by choosing a lifetime value that is
            greater than 0 and less than or equal to the minimum of
            the requested value and the value specified by object
            midcomConfigMaxLifetime:

             0 <= lt_granted <= MINIMUM(lt_requested, lt_maximum)

            where:
               - lt_granted is the actually granted lifetime by the
                 MIDCOM-MIB implementation
               - lt_requested is the requested lifetime of the MIDCOM
                 client
               - lt_maximum is the value of object
                 midcomConfigMaxLifetime

            SNMP SET requests to this object may be rejected or the
            value of the object after an accepted SET operation may be
            less than the value that was contained in the SNMP SET
            request."
       ::= { midcomGroupEntry 3 }

   --
   -- Configuration Objects
   --
   --  Configuration objects that can be used for retrieving
   --  middlebox capability information (mandatory) and for
   --  setting parameters of the implementation of transaction
   --  objects (optional).
   --
   --  Note that typically configuration objects are not intended
   --  to be written by MIDCOM clients.  In general, write access
   --  to these objects needs to be restricted more strictly than
   --  write access to transaction objects.
   --

   --
   -- Capabilities subtree
   --
   -- This subtree contains objects to which MIDCOM clients should
   -- have read access.
   --

   midcomConfigMaxLifetime OBJECT-TYPE
       SYNTAX      Unsigned32
       UNITS       "seconds"



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       MAX-ACCESS  read-write
       STATUS      current
       DESCRIPTION
           "When retrieved, this object returns the maximum lifetime,
            in seconds, that this middlebox allows policy rules to
            have."
       ::= { midcomConfig 1 }

   midcomConfigPersistentRules OBJECT-TYPE
       SYNTAX      TruthValue
       MAX-ACCESS  read-write
       STATUS      current
       DESCRIPTION
           "When retrieved, this object returns true(1) if the
            MIDCOM-MIB implementation can store policy rules
            persistently.  Otherwise, it returns false(2).

            A value of true(1) indicates that there may be
            entries in the midcomRuleTable with object
            midcomRuleStorageType set to value nonVolatile(3)."
       ::= { midcomConfig 2 }

   midcomConfigIfTable OBJECT-TYPE
       SYNTAX      SEQUENCE OF MidcomConfigIfEntry
       MAX-ACCESS  not-accessible
       STATUS      current
       DESCRIPTION
           "This table indicates capabilities of the MIDCOM-MIB
            implementation per IP interface.

            The table is indexed by the object midcomConfigIfIndex.

            For indexing a single interface, this object contains
            the value of the ifIndex object that is associated
            with the interface.  If an entry with
            midcomConfigIfIndex = 0 occurs, then bits set in
            objects of this entry apply to all interfaces for which
            there is no entry in this table with the interface's
            index."
       ::= { midcomConfig 3 }

   midcomConfigIfEntry OBJECT-TYPE
       SYNTAX      MidcomConfigIfEntry
       MAX-ACCESS  not-accessible
       STATUS      current
       DESCRIPTION
           "An entry describing the capabilities of a middlebox
            with respect to the indexed IP interface."



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       INDEX { midcomConfigIfIndex }
       ::= { midcomConfigIfTable 1 }

   MidcomConfigIfEntry ::= SEQUENCE {
       midcomConfigIfIndex          InterfaceIndexOrZero,
       midcomConfigIfBits           BITS,
       midcomConfigIfEnabled        TruthValue
   }

   midcomConfigIfIndex OBJECT-TYPE
       SYNTAX      InterfaceIndexOrZero
       MAX-ACCESS  not-accessible
       STATUS      current
       DESCRIPTION
           "The index of an entry in the midcomConfigIfTable.

            For values different from zero, this object
            identifies an IP interface by containing the same
            value as the ifIndex object associated with the
            interface.

            Note that the index of a particular interface in the
            ifTable may change after a re-initialization of the
            middlebox, for example, after adding another interface to
            it.  In such a case, the value of this object may change,
            but the interface referred to by the MIDCOM-MIB MUST still
            be the same.  If, after a re-initialization of the
            middlebox, the interface referred to before
            re-initialization cannot be uniquely mapped anymore to a
            particular entry in the ifTable, then the value of object
            midcomConfigIfEnabled of the same entry MUST be changed to
            false(2).

            If the object has a value of 0, then values
            specified by further objects of the same entry
            apply to all interfaces for which there is no
            explicit entry in the midcomConfigIfTable."
       ::= { midcomConfigIfEntry 1 }

   midcomConfigIfBits OBJECT-TYPE
       SYNTAX      BITS {
                       ipv4(0),
                       ipv6(1),
                       addressWildcards(2),
                       portWildcards(3),
                       firewall(4),
                       nat(5),
                       portTranslation(6),



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                       protocolTranslation(7),
                       twiceNat(8),
                       inside(9)
                   }
       MAX-ACCESS  read-only
       STATUS      current
       DESCRIPTION
           "When retrieved, this object returns a set of bits
            indicating the capabilities (or configuration) of
            the middlebox with respect to the referenced IP interface.
            If the index equals 0, then all set bits apply to all
            interfaces.

            If the ipv4(0) bit is set, then the middlebox supports
            IPv4 at the indexed IP interface.

            If the ipv6(1) bit is set, then the middlebox supports
            IPv6 at the indexed IP interface.

            If the addressWildcards(2) bit is set, then the
            middlebox supports IP address wildcarding at the indexed
            IP interface.

            If the portWildcards(3) bit is set, then the
            middlebox supports port wildcarding at the indexed
            IP interface.

            If the firewall(4) bit is set, then the middlebox offers
            firewall functionality at the indexed interface.

            If the nat(5) bit is set, then the middlebox offers
            network address translation service at the indexed
            interface.

            If the portTranslation(6) bit is set, then the middlebox
            offers port translation service at the indexed interface.
            This bit is only relevant if nat(5) is set.

            If the protocolTranslation(7) bit is set, then the
            middlebox offers protocol translation service between
            IPv4 and IPv6 at the indexed interface.  This bit is only
            relevant if nat(5) is set.

            If the twiceNat(8) bit is set, then the middlebox offers
            twice network address translation service at the indexed
            interface.  This bit is only relevant if nat(5) is set.

            If the inside(9) bit is set, then the indexed interface is



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            an inside interface with respect to NAT functionality.
            Otherwise, it is an outside interface.  This bit is only
            relevant if nat(5) is set.  An SNMP agent supporting both
            the MIDCOM-MIB module and the NAT-MIB module SHOULD ensure
            that the value of this object is consistent with the values
            of corresponding objects in the NAT-MIB module."
       ::= { midcomConfigIfEntry 2 }

   midcomConfigIfEnabled OBJECT-TYPE
       SYNTAX      TruthValue
       MAX-ACCESS  read-write
       STATUS      current
       DESCRIPTION
           "The value of this object indicates the availability of
            the middlebox service described by midcomConfigIfBits
            at the indexed IP interface.

            By writing to this object, the MIDCOM support for the
            entire IP interface can be switched on or off.  Setting
            this object to false(2) immediately stops middlebox
            support at the indexed IP interface.  This implies that
            all policy rules that use NAT or firewall resources at
            the indexed IP interface are terminated immediately.
            In this case, the MIDCOM agent MUST send
            midcomUnsolicitedRuleEvent to all MIDCOM clients that
            have access to one of the terminated rules."
       DEFVAL { true }
       ::= { midcomConfigIfEntry 3 }

   --
   -- Firewall subtree
   --
   -- This subtree contains the firewall configuration table
   --

   midcomConfigFirewallTable OBJECT-TYPE
       SYNTAX      SEQUENCE OF MidcomConfigFirewallEntry
       MAX-ACCESS  not-accessible
       STATUS      current
       DESCRIPTION
          "This table lists the firewall configuration per IP interface.

           It can be used for configuring how policy rules created by
           MIDCOM clients are realized as firewall rules of a firewall
           implementation.  Particularly, the priority used for MIDCOM
           policy rules can be configured.  For a single firewall
           implementation at a particular IP interface, all MIDCOM
           policy rules are realized as firewall rules with the same



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           priority.  Also, a firewall rule group name can be
           configured.

           The table is indexed by the object midcomConfigFirewallIndex.
           For indexing a single interface, this object contains the
           value of the ifIndex object that is associated with the
           interface.  If an entry with midcomConfigFirewallIndex = 0
           occurs, then bits set in objects of this entry apply to all
           interfaces for which there is no entry in this table for the
           interface's index."
       ::= { midcomConfig 4 }

   midcomConfigFirewallEntry OBJECT-TYPE
       SYNTAX      MidcomConfigFirewallEntry
       MAX-ACCESS  not-accessible
       STATUS      current
       DESCRIPTION
          "An entry describing a particular set of
           firewall resources."
       INDEX { midcomConfigFirewallIndex }
       ::= { midcomConfigFirewallTable 1 }

   MidcomConfigFirewallEntry ::= SEQUENCE {
       midcomConfigFirewallIndex      InterfaceIndexOrZero,
       midcomConfigFirewallGroupId    SnmpAdminString,
       midcomConfigFirewallPriority   Unsigned32
   }

   midcomConfigFirewallIndex OBJECT-TYPE
       SYNTAX      InterfaceIndexOrZero
       MAX-ACCESS  not-accessible
       STATUS      current
       DESCRIPTION
           "The index of an entry in the midcomConfigFirewallTable.

            For values different from 0, this object identifies an
            IP interface by containing the same value as the ifIndex
            object associated with the interface.

            Note that the index of a particular interface in the
            ifTable may change after a re-initialization of the
            middlebox, for example, after adding another interface to
            it.  In such a case, the value of this object may change,
            but the interface referred to by the MIDCOM-MIB MUST still
            be the same.  If, after a re-initialization of the
            middlebox, the interface referred to before
            re-initialization cannot be uniquely mapped anymore to a
            particular entry in the ifTable, then the entry in the



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            midcomConfigFirewallTable MUST be deleted.

            If the object has a value of 0, then values specified by
            further objects of the same entry apply to all interfaces
            for which there is no explicit entry in the
            midcomConfigFirewallTable."
       ::= { midcomConfigFirewallEntry 1 }

   midcomConfigFirewallGroupId OBJECT-TYPE
       SYNTAX      SnmpAdminString
       MAX-ACCESS  read-write
       STATUS      current
       DESCRIPTION
          "The firewall rule group to which all firewall rules are
           assigned that the MIDCOM server creates for the interface
           indicated by object midcomConfigFirewallIndex.  If the
           value of object midcomConfigFirewallIndex is 0, then all
           firewall rules of the MIDCOM server that are created for
           interfaces with no specific entry in the
           midcomConfigFirewallTable are assigned to the firewall
           rule group indicated by the value of this object."
       ::= { midcomConfigFirewallEntry 2 }

   midcomConfigFirewallPriority OBJECT-TYPE
       SYNTAX      Unsigned32
       MAX-ACCESS  read-write
       STATUS      current
       DESCRIPTION
          "The priority assigned to all firewall rules that the
           MIDCOM server creates for the interface indicated by
           object midcomConfigFirewallIndex.  If the value of object
           midcomConfigFirewallIndex is 0, then this priority is
           assigned to all firewall rules of the MIDCOM server that
           are created for interfaces for which there is no specific
           entry in the midcomConfigFirewallTable."
       ::= { midcomConfigFirewallEntry 3 }

   --
   -- Monitoring Objects
   --
   -- Monitoring objects are structured into two groups,
   -- the midcomResourceGroup providing information about used
   -- resources and the midcomStatisticsGroup providing information
   -- about MIDCOM transaction statistics.

   --
   -- Resources subtree
   --



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   -- The MIDCOM resources subtree contains a set of managed
   -- objects describing the currently used resources of NAT
   -- and firewall implementations.
   --

   --
   -- Textual conventions for objects of the resource subtree
   --

   MidcomNatBindMode ::= TEXTUAL-CONVENTION
       STATUS      current
       DESCRIPTION
          "An indicator of the kind of NAT resources used by a policy
           rule.  This definition corresponds to the definition of
           NatBindMode in the NAT-MIB (RFC 4008).  Value none(3) can
           be used to indicate that the policy rule does not use
           any NAT binding.
           "
       SYNTAX      INTEGER {
                       addressBind(1),
                       addressPortBind(2),
                       none(3)
                   }

   MidcomNatSessionIdOrZero ::= TEXTUAL-CONVENTION
       DISPLAY-HINT "d"
       STATUS      current
       DESCRIPTION
          "A unique ID that is assigned to each NAT session by
           a NAT implementation.  This definition corresponds to
           the definition of NatSessionId in the NAT-MIB (RFC 4008).
           Value 0 can be used to indicate that the policy rule does
           not use any NAT binding."
       SYNTAX      Unsigned32

   --
   -- The MIDCOM resource table
   --

   midcomResourceTable OBJECT-TYPE
       SYNTAX      SEQUENCE OF MidcomResourceEntry
       MAX-ACCESS  not-accessible
       STATUS      current
       DESCRIPTION
          "This table lists all used middlebox resources per
           MIDCOM policy rule.

           The midcomResourceTable augments the



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           midcomRuleTable."
       ::= { midcomMonitoring 1 }

   midcomResourceEntry OBJECT-TYPE
       SYNTAX      MidcomResourceEntry
       MAX-ACCESS  not-accessible
       STATUS      current
       DESCRIPTION
          "An entry describing a particular set of middlebox
           resources."
       AUGMENTS { midcomRuleEntry }
       ::= { midcomResourceTable 1 }

   MidcomResourceEntry ::= SEQUENCE {
       midcomRscNatInternalAddrBindMode   MidcomNatBindMode,
       midcomRscNatInternalAddrBindId     NatBindIdOrZero,
       midcomRscNatInsideAddrBindMode     MidcomNatBindMode,
       midcomRscNatInsideAddrBindId       NatBindIdOrZero,
       midcomRscNatSessionId1             MidcomNatSessionIdOrZero,
       midcomRscNatSessionId2             MidcomNatSessionIdOrZero,
       midcomRscFirewallRuleId            Unsigned32
   }

   midcomRscNatInternalAddrBindMode OBJECT-TYPE
       SYNTAX      MidcomNatBindMode
       MAX-ACCESS  read-only
       STATUS      current
       DESCRIPTION
          "An indication of whether this policy rule uses an address
           NAT bind or an address-port NAT bind for binding the
           internal address.

           If the MIDCOM-MIB module is operated together with
           the NAT-MIB module (RFC 4008) then object
           midcomRscNatInternalAddrBindMode contains the same
           value as the corresponding object
           natSessionPrivateSrcEPBindMode of the NAT-MIB module."
       ::= { midcomResourceEntry 4 }

   midcomRscNatInternalAddrBindId OBJECT-TYPE
       SYNTAX      NatBindIdOrZero
       MAX-ACCESS  read-only
       STATUS      current
       DESCRIPTION
          "This object references to the allocated internal NAT
           bind that is used by this policy rule.  A NAT bind
           describes the mapping of internal addresses to
           outside addresses.  MIDCOM-MIB implementations can



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           read this object to learn the corresponding NAT bind
           resource for this particular policy rule.

           If the MIDCOM-MIB module is operated together with
           the NAT-MIB module (RFC 4008) then object
           midcomRscNatInternalAddrBindId contains the same
           value as the corresponding object
           natSessionPrivateSrcEPBindId of the NAT-MIB module."
       ::= { midcomResourceEntry 5 }

   midcomRscNatInsideAddrBindMode OBJECT-TYPE
       SYNTAX      MidcomNatBindMode
       MAX-ACCESS  read-only
       STATUS      current
       DESCRIPTION
          "An indication of whether this policy rule uses an address
           NAT bind or an address-port NAT bind for binding the
           external address.

           If the MIDCOM-MIB module is operated together with
           the NAT-MIB module (RFC 4008), then object
           midcomRscNatInsideAddrBindMode contains the same
           value as the corresponding object
           natSessionPrivateDstEPBindMode of the NAT-MIB module."
       ::= { midcomResourceEntry 6 }

   midcomRscNatInsideAddrBindId OBJECT-TYPE
       SYNTAX      NatBindIdOrZero
       MAX-ACCESS  read-only
       STATUS      current
       DESCRIPTION
          "This object refers to the allocated external NAT
           bind that is used by this policy rule.  A NAT bind
           describes the mapping of external addresses to
           inside addresses.  MIDCOM-MIB implementations can
           read this object to learn the corresponding NAT bind
           resource for this particular policy rule.

           If the MIDCOM-MIB module is operated together with the
           NAT-MIB module (RFC 4008), then object
           midcomRscNatInsideAddrBindId contains the same
           value as the corresponding object
           natSessionPrivateDstEPBindId of the NAT-MIB module."
       ::= { midcomResourceEntry 7 }

   midcomRscNatSessionId1 OBJECT-TYPE
       SYNTAX      MidcomNatSessionIdOrZero
       MAX-ACCESS  read-only



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       STATUS      current
       DESCRIPTION
          "This object refers to the first allocated NAT session for
           this policy rule.  MIDCOM-MIB implementations can read this
           object to learn whether or not a NAT session for a
           particular policy rule is used.  A value of 0 means that no
           NAT session is allocated for this policy rule.  A value
           other than 0 refers to the NAT session."
      ::= { midcomResourceEntry 8 }

   midcomRscNatSessionId2 OBJECT-TYPE
       SYNTAX      MidcomNatSessionIdOrZero
       MAX-ACCESS  read-only
       STATUS      current
       DESCRIPTION
          "This object refers to the second allocated NAT session for
           this policy rule.  MIDCOM-MIB implementations can read this
           object to learn whether or not a NAT session for a
           particular policy rule is used.  A value of 0 means that no
           NAT session is allocated for this policy rule.  A value
           other than 0 refers to the NAT session."
       ::= { midcomResourceEntry 9 }

   midcomRscFirewallRuleId OBJECT-TYPE
       SYNTAX      Unsigned32
       MAX-ACCESS  read-only
       STATUS      current
       DESCRIPTION
          "This object refers to the allocated firewall
           rule in the firewall engine for this policy rule.
           MIDCOM-MIB implementations can read this value to
           learn whether a firewall rule for this particular
           policy rule is used or not.  A value of 0 means that
           no firewall rule is allocated for this policy rule.
           A value other than 0 refers to the firewall rule
           number within the firewall engine."
       ::= { midcomResourceEntry 10 }

   --
   -- Statistics subtree
   --
   -- The MIDCOM statistics subtree contains a set of managed
   -- objects providing statistics about the usage of transaction
   -- objects.
   --

   midcomStatistics      OBJECT IDENTIFIER ::= { midcomMonitoring 2 }




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   midcomCurrentOwners OBJECT-TYPE
       SYNTAX      Gauge32
       MAX-ACCESS  read-only
       STATUS      current
       DESCRIPTION
          "The number of different values for midcomRuleOwner
           for all current entries in the midcomRuleTable."
       ::= { midcomStatistics 1 }

   midcomTotalRejectedRuleEntries OBJECT-TYPE
       SYNTAX      Counter32
       MAX-ACCESS  read-only
       STATUS      current
       DESCRIPTION
          "The total number of failed attempts to create an entry
           in the midcomRuleTable."
       ::= { midcomStatistics 2 }

   midcomCurrentRulesIncomplete OBJECT-TYPE
       SYNTAX      Gauge32
       MAX-ACCESS  read-only
       STATUS      current
       DESCRIPTION
          "The current number of policy rules that are incomplete.

           Policy rules are loaded via row entries in the
           midcomRuleTable.  This object counts policy rules that are
           loaded but not fully specified, i.e., they are in state
           newEntry(1) or setting(2)."
       ::= { midcomStatistics 3 }

   midcomTotalIncorrectReserveRules OBJECT-TYPE
       SYNTAX      Counter32
       MAX-ACCESS  read-only
       STATUS      current
       DESCRIPTION
          "The total number of policy reserve rules that failed
           parameter check and entered state incorrectRequest(4)."
       ::= { midcomStatistics 4 }

   midcomTotalRejectedReserveRules OBJECT-TYPE
       SYNTAX      Counter32
       MAX-ACCESS  read-only
       STATUS      current
       DESCRIPTION
          "The total number of policy reserve rules that failed
           while being processed and entered state requestRejected(6)."
       ::= { midcomStatistics 5 }



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   midcomCurrentActiveReserveRules OBJECT-TYPE
       SYNTAX      Gauge32
       MAX-ACCESS  read-only
       STATUS      current
       DESCRIPTION
          "The number of currently active policy reserve rules."
       ::= { midcomStatistics 6 }

   midcomTotalExpiredReserveRules OBJECT-TYPE
       SYNTAX      Counter32
       MAX-ACCESS  read-only
       STATUS      current
       DESCRIPTION
          "The total number of expired policy reserve rules
           (entered termination state timedOut(9))."
       ::= { midcomStatistics 7 }

   midcomTotalTerminatedOnRqReserveRules OBJECT-TYPE
       SYNTAX      Counter32
       MAX-ACCESS  read-only
       STATUS      current
       DESCRIPTION
          "The total number of policy reserve rules that were
           terminated on request (entered termination state
           terminatedOnRequest(10))."
       ::= { midcomStatistics 8 }

   midcomTotalTerminatedReserveRules OBJECT-TYPE
       SYNTAX      Counter32
       MAX-ACCESS  read-only
       STATUS      current
       DESCRIPTION
          "The total number of policy reserve rules that were
           terminated, but not on request (entered termination state
           terminated(11))."
       ::= { midcomStatistics 9 }

   midcomTotalIncorrectEnableRules OBJECT-TYPE
       SYNTAX      Counter32
       MAX-ACCESS  read-only
       STATUS      current
       DESCRIPTION
          "The total number of policy enable rules that failed
           parameter check and entered state incorrectRequest(4)."
       ::= { midcomStatistics 10 }

   midcomTotalRejectedEnableRules OBJECT-TYPE
       SYNTAX      Counter32



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       MAX-ACCESS  read-only
       STATUS      current
       DESCRIPTION
          "The total number of policy enable rules that failed
           while being processed and entered state requestRejected(6)."
       ::= { midcomStatistics 11 }
   midcomCurrentActiveEnableRules OBJECT-TYPE
       SYNTAX      Gauge32
       MAX-ACCESS  read-only
       STATUS      current
       DESCRIPTION
          "The number of currently active policy enable rules."
       ::= { midcomStatistics 12 }

   midcomTotalExpiredEnableRules OBJECT-TYPE
       SYNTAX      Counter32
       MAX-ACCESS  read-only
       STATUS      current
       DESCRIPTION
          "The total number of expired policy enable rules
           (entered termination state timedOut(9))."
       ::= { midcomStatistics 13 }

   midcomTotalTerminatedOnRqEnableRules OBJECT-TYPE
       SYNTAX      Counter32
       MAX-ACCESS  read-only
       STATUS      current
       DESCRIPTION
          "The total number of policy enable rules that were
           terminated on request (entered termination state
           terminatedOnRequest(10))."
       ::= { midcomStatistics 14 }

   midcomTotalTerminatedEnableRules OBJECT-TYPE
       SYNTAX      Counter32
       MAX-ACCESS  read-only
       STATUS      current
       DESCRIPTION
          "The total number of policy enable rules that were
           terminated, but not on request (entered termination state
           terminated(11))."
       ::= { midcomStatistics 15 }

   --
   -- Notifications.
   --

   midcomUnsolicitedRuleEvent NOTIFICATION-TYPE



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       OBJECTS     { midcomRuleOperStatus, midcomRuleLifetime }
       STATUS      current
       DESCRIPTION
           "This notification is generated whenever the value of
            midcomRuleOperStatus enters any error state or any
            termination state without an explicit trigger by a
            MIDCOM client."
       ::= { midcomNotifications 1 }

   midcomSolicitedRuleEvent NOTIFICATION-TYPE
       OBJECTS     { midcomRuleOperStatus, midcomRuleLifetime }
       STATUS      current
       DESCRIPTION
           "This notification is generated whenever the value
            of midcomRuleOperStatus enters one of the states
            {reserved, enabled, any error state, any termination state}
            as a result of a MIDCOM agent writing successfully to
            object midcomRuleAdminStatus.

            In addition, it is generated when the lifetime of
            a rule was changed by successfully writing to object
            midcomRuleLifetime."
       ::= { midcomNotifications 2 }

   midcomSolicitedGroupEvent NOTIFICATION-TYPE
       OBJECTS     { midcomGroupLifetime }
       STATUS      current
       DESCRIPTION
           "This notification is generated for indicating that the
            lifetime of all member rules of the group was changed by
            successfully writing to object midcomGroupLifetime.

            Note that this notification is only sent if the lifetime
            of a group was changed by successfully writing to object
            midcomGroupLifetime.  No notification is sent
              - if a group's lifetime is changed by writing to object
                midcomRuleLifetime of any of its member policies,
              - if a group's lifetime expires (in this case,
                notifications are sent for all member policies), or
              - if the group is terminated by terminating the last
                of its member policies without writing to object
                midcomGroupLifetime."
       ::= { midcomNotifications 3 }

   --
   -- Conformance information
   --




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   midcomCompliances OBJECT IDENTIFIER ::= { midcomConformance 1 }
   midcomGroups      OBJECT IDENTIFIER ::= { midcomConformance 2 }

   --
   -- compliance statements
   --

   -- This is the MIDCOM compliance definition ...

   --

   midcomCompliance MODULE-COMPLIANCE
       STATUS      current
       DESCRIPTION
           "The compliance statement for implementations of the
            MIDCOM-MIB module.

            Note that compliance with this compliance
            statement requires compliance with the
            ifCompliance3 MODULE-COMPLIANCE statement of the
            IF-MIB [RFC2863]."
       MODULE      -- this module
       MANDATORY-GROUPS {
               midcomRuleGroup,
               midcomNotificationsGroup,
               midcomCapabilitiesGroup,
               midcomStatisticsGroup
       }
       GROUP   midcomConfigFirewallGroup
       DESCRIPTION
          "A compliant implementation does not have to implement
           the midcomConfigFirewallGroup."
       GROUP   midcomResourceGroup
       DESCRIPTION
          "A compliant implementation does not have to implement
           the midcomResourceGroup."
       OBJECT midcomRuleInternalIpPrefixLength
       MIN-ACCESS  read-only
       DESCRIPTION
          "Write access is not required.  When write access is
           not supported, return 128 as the value of this object.
           A value of 128 means that the function represented by
           this option is not supported."
       OBJECT midcomRuleExternalIpPrefixLength
       MIN-ACCESS  read-only
       DESCRIPTION
          "Write access is not required.  When write access is
           not supported, return 128 as the value of this object.



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           A value of 128 means that the function represented by
           this option is not supported."
       OBJECT midcomRuleMaxIdleTime
       MIN-ACCESS  read-only
       DESCRIPTION
          "Write access is not required.  When write access is
           not supported, return 0 as the value of this object.
           A value of 0 means that the function represented by
           this option is not supported."
       OBJECT midcomRuleInterface
       MIN-ACCESS  read-only
       DESCRIPTION
          "Write access is not required."
       OBJECT midcomConfigMaxLifetime
       MIN-ACCESS  read-only
       DESCRIPTION
          "Write access is not required."
       OBJECT midcomConfigPersistentRules
       MIN-ACCESS  read-only
       DESCRIPTION
          "Write access is not required."
       OBJECT midcomConfigIfEnabled
       MIN-ACCESS  read-only
       DESCRIPTION
          "Write access is not required."
       OBJECT midcomConfigFirewallGroupId
       MIN-ACCESS  read-only
       DESCRIPTION
          "Write access is not required."
       OBJECT midcomConfigFirewallPriority
       MIN-ACCESS  read-only
       DESCRIPTION
          "Write access is not required."
       ::= { midcomCompliances 1 }

   midcomRuleGroup OBJECT-GROUP
       OBJECTS {
           midcomRuleAdminStatus,
           midcomRuleOperStatus,
           midcomRuleStorageType,
           midcomRuleStorageTime,
           midcomRuleError,
           midcomRuleInterface,
           midcomRuleFlowDirection,
           midcomRuleMaxIdleTime,
           midcomRuleTransportProtocol,
           midcomRulePortRange,
           midcomRuleInternalIpVersion,



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           midcomRuleExternalIpVersion,
           midcomRuleInternalIpAddr,
           midcomRuleInternalIpPrefixLength,
           midcomRuleInternalPort,
           midcomRuleExternalIpAddr,
           midcomRuleExternalIpPrefixLength,
           midcomRuleExternalPort,
           midcomRuleInsideIpAddr,
           midcomRuleInsidePort,
           midcomRuleOutsideIpAddr,
           midcomRuleOutsidePort,
           midcomRuleLifetime,
           midcomRuleRowStatus,
           midcomGroupLifetime
       }
       STATUS      current
       DESCRIPTION
           "A collection of objects providing information about
            policy rules and policy rule groups."
       ::= { midcomGroups 1 }

   midcomCapabilitiesGroup OBJECT-GROUP
       OBJECTS {
           midcomConfigMaxLifetime,
           midcomConfigPersistentRules,
           midcomConfigIfBits,
           midcomConfigIfEnabled
       }
       STATUS      current
       DESCRIPTION
           "A collection of objects providing information about
            the capabilities of a middlebox."
       ::= { midcomGroups 2 }

   midcomConfigFirewallGroup OBJECT-GROUP
       OBJECTS {
           midcomConfigFirewallGroupId,
           midcomConfigFirewallPriority
       }
       STATUS      current
       DESCRIPTION
           "A collection of objects providing information about
            the firewall rule group and firewall rule priority to
            be used by firewalls loaded through MIDCOM."
       ::= { midcomGroups 3 }

   midcomResourceGroup OBJECT-GROUP
       OBJECTS {



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           midcomRscNatInternalAddrBindMode,
           midcomRscNatInternalAddrBindId,
           midcomRscNatInsideAddrBindMode,
           midcomRscNatInsideAddrBindId,
           midcomRscNatSessionId1,
           midcomRscNatSessionId2,
           midcomRscFirewallRuleId
       }
       STATUS      current
       DESCRIPTION
           "A collection of objects providing information about
            the used NAT and firewall resources."
       ::= { midcomGroups 4 }

   midcomStatisticsGroup OBJECT-GROUP
       OBJECTS {
           midcomCurrentOwners,
           midcomTotalRejectedRuleEntries,
           midcomCurrentRulesIncomplete,
           midcomTotalIncorrectReserveRules,
           midcomTotalRejectedReserveRules,
           midcomCurrentActiveReserveRules,
           midcomTotalExpiredReserveRules,
           midcomTotalTerminatedOnRqReserveRules,
           midcomTotalTerminatedReserveRules,
           midcomTotalIncorrectEnableRules,
           midcomTotalRejectedEnableRules,
           midcomCurrentActiveEnableRules,
           midcomTotalExpiredEnableRules,
           midcomTotalTerminatedOnRqEnableRules,
           midcomTotalTerminatedEnableRules
       }
       STATUS      current
       DESCRIPTION
           "A collection of objects providing statistical
            information about the MIDCOM server."
       ::= { midcomGroups 5 }














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   midcomNotificationsGroup NOTIFICATION-GROUP
        NOTIFICATIONS {
            midcomUnsolicitedRuleEvent,
            midcomSolicitedRuleEvent,
            midcomSolicitedGroupEvent
        }
        STATUS    current
        DESCRIPTION
            "The notifications emitted by the midcomMIB."
        ::= { midcomGroups 6 }

   END

10.  Security Considerations

   Obviously, securing access to firewall and NAT configuration is
   extremely important for maintaining network security.  This section
   first describes general security issues of the MIDCOM-MIB module and
   then discusses three concrete security threats: unauthorized
   middlebox configuration, unauthorized access to middlebox
   configuration information, and unauthorized access to the MIDCOM
   service configuration.

10.1.  General Security Issues

   There are a number of management objects defined in this MIB module
   with a MAX-ACCESS clause of read-write and/or read-create.  Such
   objects may be considered sensitive or vulnerable in some network
   environments.  But also access to managed objects with a MAX-ACCESS
   clause of read-only may be considered sensitive or vulnerable.  The
   support for SET and GET operations in a non-secure environment
   without proper protection can have a negative effect on network
   operations.

   SNMP versions prior to SNMPv3 did not include adequate security.
   Even if the network itself is secure (for example by using IPsec),
   even then, there is no control as to who on the secure network is
   allowed to access and GET/SET (read/change/create/delete) the objects
   in this MIB module.

   Deployment of SNMP versions prior to SNMPv3 is NOT RECOMMENDED.

   Compliant MIDCOM-MIB implementations MUST support SNMPv3 security
   services including data integrity, identity authentication, data
   confidentiality, and replay protection.






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   It is REQUIRED that the implementations support the security features
   as provided by the SNMPv3 framework.  Specifically, the use of the
   User-based Security Model RFC 3414 [RFC3414] and the View-based
   Access Control Model RFC 3415 [RFC3415] is RECOMMENDED.

   It is then a customer/operator responsibility to ensure that the SNMP
   entity giving access to an instance of this MIB is properly
   configured to give access to the objects only to those principals
   (users) that have legitimate rights to indeed GET or SET
   (change/create/delete) them.

   To facilitate the provisioning of access control by a security
   administrator using the View-based Access Control Model (VACM)
   defined in RFC 3415 [RFC3415] for tables in which multiple users may
   need to independently create or modify entries, the initial index is
   used as an "owner index".  This is supported by the midcomRuleTable
   and the midcomGroupTable.  Each of them uses midcomRuleOwner as the
   initial index.  midcomRuleOwner has the syntax of SnmpAdminString,
   and can thus be trivially mapped to an SNMP securityName or a
   groupName as defined in VACM, in accordance with a security policy.

   All entries in the two mentioned tables belonging to a particular
   user will have the same value for this initial index.  For a given
   user's entries in a particular table, the object identifiers for the
   information in these entries will have the same subidentifiers
   (except for the "column" subidentifier) up to the end of the encoded
   owner index.  To configure VACM to permit access to this portion of
   the table, one would create vacmViewTreeFamilyTable entries with the
   value of vacmViewTreeFamilySubtree including the owner index portion,
   and vacmViewTreeFamilyMask "wildcarding" the column subidentifier.
   More elaborate configurations are possible.

10.2.  Unauthorized Middlebox Configuration

   The most dangerous threat to network security related to the MIDCOM-
   MIB module is unauthorized access to facilities for establishing
   policy rules.  In such a case, unauthorized principals would write to
   the midcomRuleTable for opening firewall pinholes and/or for creating
   NAT maps, bindings, and/or sessions.  Establishing policies can be
   used to gain access to networks and systems that are protected by
   firewalls and/or NATs.

   If this protection is removed by unauthorized access to MIDCOM-MIB
   policies, then the resulting degradation of network security can be
   severe.  Confidential information protected by a firewall might
   become accessible to unauthorized principals, attacks exploiting





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   security leaks of systems in the protected network might become
   possible from external networks, and it might be possible to stop
   firewalls blocking denial-of-service attacks.

   MIDCOM-MIB implementations MUST provide means for strict
   authentication, message integrity check, and write access control to
   managed objects that can be used for establishing policy rules.
   These are objects in the midcomRuleTable and midcomGroupTable with a
   MAX-ACCESS clause of read-write and/or read-create.

   Particularly sensitive is write access to the managed object
   midcomRuleAdminStatus, because writing it causes policy rules to be
   established.

   Also, writing to other managed objects in the two tables can make
   security vulnerable if it interferes with the authorized
   establishment of a policy rule, for example, by wildcarding a policy
   rule after the corresponding entry in the midcomRuleTable is created,
   but before the authorized owner establishes the rule by writing to
   midcomRuleAdminStatus.

   Not only unauthorized establishment, but also unauthorized lifetime
   extension of an existing policy rule may be considered sensitive or
   vulnerable in some network environments.  Therefore, means for strict
   authentication, message integrity check, and write access control to
   managed object midcomGroupLifetime MUST be provided by MIDCOM-MIB
   implementations.

10.3.  Unauthorized Access to Middlebox Configuration

   Another threat to network security is unauthorized access to entries
   in the midcomRuleTable.  The entries contain information about
   existing pinholes in the firewall and/or about the current NAT
   configuration.  This information can be used for attacking the
   internal network from outside.  Therefore, a MIDCOM-MIB
   implementation MUST also provide means for read access control to the
   midcomRuleTable.

   Also, a MIDCOM-MIB implementation SHOULD provide means for protecting
   different authenticated MIDCOM agents from each other, such that, for
   example, an authenticated user can only read entries in the
   midcomRuleTable for which the initial index midcomRuleOwner matches
   the client's SNMP securityName or VACM groupName.








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10.4.  Unauthorized Access to MIDCOM Service Configuration

   There are three objects with a MAX-ACCESS clause of read-write that
   configure the MIDCOM service: midcomConfigIfEnabled,
   midcomFirewallGroupId, and midcomFirewallPriority.

   Unauthorized writing to object midcomConfigIfEnabled can cause
   serious interruptions of network service.

   Writing to midcomFirewallGroupId and/or midcomFirewallPriority can be
   used to increase or reduce the priority of firewall rules that are
   generated when a policy rule is established in the midcomRuleTable.
   Increasing the priority might permit firewall rules generated via the
   MIDCOM-MIB module to overrule basic security rules at the firewall
   that should have higher priority than the ones generated via the
   MIDCOM-MIB module.

   Therefore, also for these objects, means for strict control of write
   access MUST be provided by a MIDCOM-MIB implementation.

11.  Acknowledgements

   This memo is based on a long history of discussion within the MIDCOM
   MIB design team.  Many thanks to Mary Barnes, Jeff Case, Wes
   Hardaker, David Harrington, and Tom Taylor for fruitful comments and
   recommendations and to Juergen Schoenwaelder acting as a very
   constructive MIB doctor.

12.  IANA Considerations

   IANA has assigned an OID for the MIB module in this document:

               Descriptor        OBJECT IDENTIFIER value
               ----------        -----------------------
               midcomMIB         { mib-2 171 }

13.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC5189]  Stiemerling, M., Quittek, J., and T. Taylor, "Middlebox
              Communication (MIDCOM) Protocol Semantics", RFC 5189,
              March 2008.







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   [RFC2578]  McCloghrie, K., Perkins, D., Schoenwaelder, J., Case, J.,
              Rose, M. and S. Waldbusser, "Structure of Management
              Information Version 2 (SMIv2)", STD 58, RFC 2578, April
              1999.

   [RFC2579]  McCloghrie, K., Perkins, D., Schoenwaelder, J., Case, J.,
              Rose, M. and S. Waldbusser, "Textual Conventions for
              SMIv2", STD 58, RFC 2579, April 1999.

   [RFC2580]  McCloghrie, K., Perkins, D., Schoenwaelder, J., Case, J.,
              Rose, M. and S. Waldbusser, "Conformance Statements for
              SMIv2", STD 58, RFC 2580, April 1999.

   [RFC2863]  McCloghrie, K. and F. Kastenholz, "The Interfaces Group
              MIB", RFC 2863, June 2000.

   [RFC3411]  Harrington, D., Presuhn, R. and B. Wijnen, "An
              Architecture for Describing Simple Network Management
              Protocol (SNMP) Management Frameworks", STD 62, RFC 3411,
              December 2002.

   [RFC3413]  Levi, D., Meyer, P., and B. Stewart, "Simple Network
              Management Protocol Applications", STD 62, RFC 3413,
              December 2002.

   [RFC3414]  Blumenthal, U. and B. Wijnen, "User-based Security Model
              (USM) for version 3 of the Simple Network Management
              Protocol (SNMPv3)", STD 62, RFC 3414, December 2002.

   [RFC3418]  Presuhn, R., Ed., "Management Information Base (MIB) for
              the Simple Network Management Protocol (SNMP)", STD 62,
              RFC 3418, December 2002.

   [RFC3550]  Schulzrinne, H., Casner, S., Frederick, R., and V.
              Jacobson, "RTP: A Transport Protocol for Real-Time
              Applications", STD 64, RFC 3550, July 2003.

   [RFC4001]  Daniele, M., Haberman, B., Routhier, S., and J.
              Schoenwaelder, "Textual Conventions for Internet Network
              Addresses", RFC 4001, February 2005.

   [RFC4008]  Rohit, R., Srisuresh, P., Raghunarayan, R., Pai, N., and
              C. Wang, "Definitions of Managed Objects for Network
              Address Translators (NAT)", RFC 4008, March 2005.







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14.  Informative References

   [RFC3410]  Case, J., Mundy, R., Partain, D. and B. Stewart,
              "Introduction and Applicability Statements for Internet-
              Standard Management Framework", RFC 3410, December 2002.

   [RFC3234]  Carpenter, B. and S. Brim, "Middleboxes: Taxonomy and
              Issues", RFC 3234, February 2002.

   [RFC3303]  Srisuresh, P., Kuthan, J., Rosenberg, J., Molitor, A., and
              A. Rayhan, "Middlebox communication architecture and
              framework", RFC 3303, August 2002.

   [RFC3304]  Swale, R., Mart, P., Sijben, P., Brim, S., and M. Shore,
              "Middlebox Communications (midcom) Protocol Requirements",
              RFC 3304, August 2002.

   [RFC3415]  Wijnen, B., Presuhn, R., and K. McCloghrie, "View-based
              Access Control Model (VACM) for the Simple Network
              Management Protocol (SNMP)", STD 62, RFC 3415, December
              2002.






























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Authors' Addresses

   Juergen Quittek
   NEC Europe Ltd.
   Kurfuersten-Anlage 36
   69115 Heidelberg
   Germany

   Phone: +49 6221 4342-115
   EMail: quittek@nw.neclab.eu


   Martin Stiemerling
   NEC Europe Ltd.
   Kurfuersten-Anlage 36
   69115 Heidelberg
   Germany

   Phone: +49 6221 4342-113
   EMail: stiemerling@nw.neclab.eu


   Pyda Srisuresh
   Kazeon Systems, Inc.
   1161 San Antonio Rd.
   Mountain View, CA 94043
   U.S.A.

   Phone: +1 408 836 4773
   EMail: srisuresh@yahoo.com





















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