Subject: DVMRP Question

From: Paul Gray <[email-masked]>
Date: Mon, 03 Feb 1997 09:46:33 -0500

I have a question about DVMRP. Does DVMRP allow for static
DVMRP routes to be configured? Looking at Cisco documentation
it appeared that the ip mroute command could be used for this.
If so do other vendors also allow static DVMRP routes?

Thanks, for any help.
Paul

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From: Tom Pusateri <[email-masked]>
Date: Mon, 03 Feb 1997 10:59:31 -0500

>If so do other vendors also allow static DVMRP routes?

This is really outside the scope of the protocol and is more a
feature/mis-feature of the implementation.

It is a bit dangerous since allowing arbitrary static routes can
break routing for everyone and so I do not encourage it.

There are two cases that I can think of to consider:

1. The static route you want to advertise is an aggregate of a collection
   of routes within your domain and rather than advertise a number of
   smaller routes, you would prefer to advertise one or more aggregate routes.

2. You have a region within your domain that is running another multicast
   routing protocol and you want to advertise that region into DVMRP for
   global connectivity.

Case 1 is better acheived through some sort of aggregation statement that
only generates the aggregate when one or more of its components are present.

Case 2 needs to be done with a routing policy engine that determines which
unicast routes in non-DVMRP regions get injected into DVMRP.
This is more complicated than one might think and many vendors are currently
working on solutions for this.

Tom

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From: Dino Farinacci <[email-masked]>
Date: Mon, 3 Feb 1997 08:36:41 -0800

>> If so do other vendors also allow static DVMRP routes?

    These are static routes to multicast sources and are independently used.
    They are not related to any specific multicast routing protocol.

Dino

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From: Dino Farinacci <[email-masked]>
Date: Mon, 3 Feb 1997 08:40:42 -0800

>> break routing for everyone and so I do not encourage it.

    The same for unicast static routing too. So what is your point?

    Also, it doesn't break routing for everyone. Just from that set of
    sources described by the static route.

Dino

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From: Paul Gray <[email-masked]>
Date: Mon, 03 Feb 1997 11:49:39 -0500

Thanks, for the replies. I am working on a project that creates a
situation where a multicast host would be forwarding multicast traffic
to a Cisco router. The problem is that the Cisco router would not be
participating in DVMRP with the next hop router to this host and I am
not creating a tunnel. The Cisco will be participating in IGMP on this
LAN.I know this sounds weird. The intermediate router would forward
multicast traffic onto the local lan between itself and the Cisco. I am
looking for a mechanism to allow the source traffic to be forwarded by
the Cisco and not thrown away because the source for this data is not in
the DVMRP unicast routing table. Can I use the ip mroute command for
this?

When I specify an IP Mroute does DVMRP use these routes when checking
multicast traffic to determine if this is the appropiate interface to
recieve this traffic?

Thanks, for any help.
Paul

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From: Tom Pusateri <[email-masked]>
Date: Mon, 03 Feb 1997 11:56:14 -0500

>    The same for unicast static routing too. So what is your point?

Static routing for multicast is more dangerous than for unicast since,
in the current topology, unicast borders are protected by BGP policy
but in many cases, there is no such thing as a multicast border between
administrative authorities.  This isn't to say that it couldn't be put
in place, but currently, it isn't there.

Even though I know Steve Deering is cringing right now as the words
multicast and policy are used in the same sentence, its a fact of life.

>    sources described by the static route.

Yes. This is what I meant. Of course, this does generalize to everyone
when the static route is default.  :-)

Tom

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From: Dino Farinacci <[email-masked]>
Date: Mon, 3 Feb 1997 09:04:15 -0800

>> in place, but currently, it isn't there.

    We implement this in our DVMRP implementation. So multicast static routing
    can't damage the MBONE as a whole.

>> multicast and policy are used in the same sentence, its a fact of life.

    I agree with you.

>> when the static route is default.  :-)

    Modulo more specific routes.

Dino

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From: Steve Deering <[email-masked]>
Date: Mon, 3 Feb 1997 14:40:28 -0800

> multicast and policy are used in the same sentence, its a fact of life.

Yeah, but our job is to change the facts of life, to make a better world.
(Each of us has our own definition of "better", of course.)

Steve

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From: Dino Farinacci <[email-masked]>
Date: Mon, 3 Feb 1997 19:36:06 -0800

>> LAN.I know this sounds weird. The intermediate router would forward

    Not really. We know of several products that do this.

>> the DVMRP unicast routing table. Can I use the ip mroute command for

    Yes.

>> multicast traffic to determine if this is the appropiate interface to

    IP multicast forwarding uses the static mroutes for the RPF check and 
    therefore determines the appropriate interface.

Dino