Subject: RE: Cisco's DVMRP Discovery ?

From: Arlie Davis <[email-masked]>
Date: Wed, 5 Mar 1997 12:12:23 -0500

No, you are wrong.

Two Ciscos connected by either a GRE tunnel or a physical interface use
PIM, either sparse mode or dense mode, to do multicast routing.
Additionally, the two machines can be configured to exchange DVMRP
routes, and can be configured to prefer DVMRP routes over their own
unicast routing tables.

However, they still use the mechanisms of PIM to determine what traffic
is sent across the link.  They do not use the DVMRP prune/graft
messages.  This is the fundamental difference.

-- arlie

>-----Original Message-----
>From:	Jesus Maria Arango - Ing. Comunicaciones FSM LTDA.
>[SMTP:[email-masked]]
>Sent:	Wednesday, March 05, 1997 1:36 AM
>To:	Dave Rubin; [email-masked]
>Subject:	RE: Cisco's DVMRP Discovery ?
>
>Tell me if I'm wrong... 
>
>In this case of a GRE tunnel configured to do "dvmrp unicast-routing", the
>2 cisco routers would be exchanging DVMRP routes and the forwarding of
>multicast packets comming on either interface of the tuunel would be
>computed by the DVMRP protocol and also the prunes and grafts would be
>comming from DVMRP. This means that the 2 routers are not speaking PIM at
>all. They would consider the other router a DVMRP machine. So there is no
>sense in saying "GRE tunnel running PIM". Am I right ?
>
>- Jesus
>
>
>

---

From: "Jesus Maria Arango - Ing. Comunicaciones FSM LTDA." <[email-masked]>
Date: Wed, 5 Mar 1997 12:19:10 +0500 (GMT)

> messages.  This is the fundamental difference.

Does this mean that a cisco router uses the DVMRP table only to decide if
the incoming packet came on a tunnel that is on the shortest path to the
source but that the forwarding of that packet is done using PIM's
mechanish instead of trying to find out if the router is on the shortest
path between a neighbor who is to receive the multicast packet and the
source of such packet?

- Jesus