Subject: Cisco SPT setup

From: "Frank P. Troy" <[email-masked]>
Date: Thu, 20 Nov 1997 13:00:51 +0000

As stated in the PIM-SM RFC: "A router with directly-connected 
members first joins the  shared  RP-tree.  The  router  can  switch 
to a source's shortest path tree  (SP- tree) after receiving packets 
from that source over  the shared  RP- tree. The recommended policy 
is to initiate the switch to the SP-tree after receiving  a  
significant  number  of  data  packets  during  a specified  time  
interval  from  a particular source."

In lab testing PIM-SM Cisco IOS 11.2(9.2) I've noticed that this 
cutover from the shared RP-tree to the SP-Tree seems immediate with 
no threshold involved.

Can anyone tell me if Cisco implements a threshold and if so what is 
its upper limit?

Thanks
Frank
--------------------------------------------
Frank P. Troy          Phone:   703-471-3694
Sr. Network Engineer   Fax:     703-471-1575
AT&T DISC Development  Page:    888-808-0593 
3001 Centreville Rd.   e-mail:  [email-masked]    
Herndon, VA 20171

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From: Chris White <[email-masked]>
Date: Thu, 20 Nov 97 10:37:15 PST

> Can anyone tell me if Cisco implements a threshold and if so what is 

The threshold is configurable via the following command:

  [no] ip pim spt-threshold <kbps> | infinity [group-list <acl>]
        Configures when a PIM leaf router should join the shortest path 
        source-tree for the specified group. <kbps> is the traffic rate
        in kilobits per second. If a source sends at a rate greater than
        or equal to <kbps>, a PIM Join message is triggered towards the
        source to construct a source-tree. If "infinity" is used, all sources
        for the specified group will use the shared-tree. Specifying a
        "group-list" indicates what groups the spt-threshold applies to.
        <acl> is a reference to a simple IP access-list. When a value of 0 is
        specified or the group-list parameter is not used, the threshold
        applies to all groups. The default setting (when this command is
        not used), is to join the shortest path tree immediately after the 
        first packet arrives from a new source. [11.1]

-Chris

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From: "John M. Zwiebel" <[email-masked]>
Date: Thu, 20 Nov 1997 13:33:39 -0800

ftp://ftp-eng.cisco.com/ipmulticast/Multicast-Commands lists the
command that you need to implement this.

    
    
    Thanks
    Frank

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	John Zwiebel                       Phone: 408-526-5303
	Cisco Systems Inc.                 
	Multimedia Group                   

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