Subject: Re: Cisco's DVMRP Discovery ?

From: Bill Fenner <[email-masked]>
Date: Tue, 4 Mar 1997 15:38:16 PST

>Cisco does support GRE tunnels between two cisco routers.

To get GRE tunnels to work the way you expect an mrouted tunnel to,
add "ip dvmrp unicast-routing" to the tunnel configuration.  Only
do this if you need to (e.g. you're doing transit or your multicast
and unicast topologies diverge); if this is just a tunnel to a stub
you could point the other end's multicast default route to the tunnel.

  Bill

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From: Yves Lepage <[email-masked]>
Date: Wed, 5 Mar 97 07:36:12 -0500

Hi,

Won't that create that unicast routing injection in the DVMRP table
problem we've seen over the last years?

Regards,
Yves

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From: John Hawkinson <[email-masked]>
Date: Wed, 5 Mar 1997 09:05:43 -0500 (EST)

> problem we've seen over the last years?

No.

"ip dvmrp unicast-routing" causes IOS to speak DVMRP over an interface
it would otherwise not (such as a GRE tunnel).

It does not cause routes to be injected into DVMRP.

You have to shoot yourself in the foot differently to acheive
that.

--jhawk

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From: "Jesus Maria Arango - Ing. Comunicaciones FSM LTDA." <[email-masked]>
Date: Wed, 5 Mar 1997 11:46:30 +0500 (GMT)

> It does not cause routes to be injected into DVMRP.

I would think it does inject static routes on DVMRP because the routers
are running both PIM and DVMRP and the both have unicast and multicast
tables. I guess both routers have to transmit both static and multicast
routes to their neighbor in order for their neighbor to see the complete
network.

This does not happen if the 2 routers would be purely DVMRP because they
only exchange multicast routing entries.

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From: "Daniel A. Alvarez" <[email-masked]>
Date: Wed, 05 Mar 1997 09:31:27 -0800

> routes to their neighbor in order for their neighbor to see the complete

	You have to explicitly configure the cisco to inject routes
	(other than the ones directly connected) into the dvmrp unicast 
	table by using the "ip dvmrp metric" command.  You need to 
	be careful with this command and ensure you use an access-list
	with it.

	Please look at the documentation on 
	ftp://ftp-eng.cisco.com/ipmulticast

	This is all documented there...

dan

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From: Bill Fenner <[email-masked]>
Date: Wed, 5 Mar 1997 08:39:56 PST

>problem we've seen over the last years?

Nope, that's "ip dvmrp metric N" that usually causes the problem.
(The correct command is usually "ip dvmrp metric N A" where A is
an access-list listing the routes to be advertised)

  Bill

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From: "John M. Zwiebel" <[email-masked]>
Date: Wed, 05 Mar 1997 11:25:46 -0800

>	ftp://ftp-eng.cisco.com/ipmulticast

	ftp://ftp-eng.cisco.com/ipmulticast.html
                                           ^^^^^

	IF, you want the web page interface.

	z