Subject: Re: Mrouted on Windows NT

From: [email-masked] (Kevin C. Almeroth)
Date: Tue, 15 Oct 1996 13:57:22 -0400 (EDT)

>>    I certainly hear feedback from users trying to deploy multicast and that
>>    is low on their list of obstacles. The main issues I hear are:
>>
>>	o How do I transition from tunnels to native multicast
>>        o How do I interwork DVMRP and PIM

So what is the answer to the second?

-Kevin Almeroth

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From: "Daniel A. Alvarez" <[email-masked]>
Date: Tue, 15 Oct 1996 11:27:58 -0700

> So what is the answer to the second?

	Look in ftp://ftp.cisco.com/ipmulticast/ for some PIM-DVMRP
	interoperability documents.  You might want to start with 
	Quickstart-dvmrp.  Send mail to [email-masked]
	if you run into any problems.

dan

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From: Dino Farinacci <[email-masked]>
Date: Tue, 15 Oct 1996 11:40:24 -0700

>> So what is the answer to the second?

    If the topologies are congruent, then interaction between DVMRP and
    dense-mode PIM is pretty much plug-and-play. Since they both use RPF
    and source-trees, the distribution trees are merged seamlessly. Prunes
    and Grafts are mapped from one domain to the other.

    When topologies are not congruent, that typically lends to most of the
    problems folks have seen. If the unicast reachability information is
    not consistent, the source-trees form loops. It gets more complicated
    when sparse-mode PIM is used because a shared-tree may have conflicts
    with a DVMRP source-tree. So trying to make the topologies congruent
    and have them deviate at well-known managed points is the best way
    to deal with non-congruency. Using DVMRP unicast routing in ciscos or
    static multicast routes helps you do this.

    When interworking with DVMRP and sparse-mode PIM, you have to get DVMRP
    source's packets to the PIM RP so PIM receivers can get the data. This
    can be accomplished by putting the RP at the border router which runs
    both DVMRP and PIM. If you put the RP at an internal router inside the
    PIM cloud, a cisco border router will send PIM Register messages to
    the RP so data packets can make it to PIM receivers. For PIM source's
    packets to get to DVMRP receivers, you have to get the DVMRP/PIM border
    router to drag down the packets. In ciscos, as long as there is a source
    in the DVMRP cloud sending to that group, the border router will capture
    state about the group and start sending Joins to the RP. That will cause
    data to be dragged down to the border router, so it can forward the data 
    into the DVMRP domain.

    That's how it works today with cisco's implemenation of PIMv1. We have
    learned a lot from this experience and will incorporate slightly different
    techniques for DVMRP to PIM-SM interaction for PIMv2. We have a separate
    Internet Draft that documents this.

Dino

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From: "John M. Zwiebel" <[email-masked]>
Date: Tue, 15 Oct 1996 11:49:34 -0700

>So what is the answer to the second?

Read..

ftp://ftpeng.cisco.com/ftp/ipmulticast/Quickstart-dvmrp

But the simple answer is that on your cisco router you configure

	ip multicast-routing
	!
	interface <int>
	ip pim dense-mode
	!

and it works.

Of course, then you have to worry about RPF and non-congurence of
routing topologies and the amount of traffic you want forwarded and 
a number of other problems that continue to be discussed here.  

Basically, the interoperation between PIM and DVMRP is fairly trivial, the
hard part is understanding what that interoperation means and modifying
your router configuration to get it to be "just right".

z