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Catalyst 3550 Multilayer Switch Software Configuration Guide
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Chapter24 Configuring IP Multicast Routing
Configuring Advanced DVMRP Interoperability Features
Configuring Advanced DVMRP Interoperability Features
Cisco routers and multilayer switches run PIM to forward multicast packets to receivers and receive
multicast packets from senders. It is also possible to propagate DVMRP routes in to an d thro ugh a PIM
cloud. PIM uses this information; however, Cisco routers and multilayer switches do not implement
DVMRP to forward multicast packets.
This section describes how to perform advanced optional configuration tasks on your multilayer switch
to interoperate with DVMRP devices. It contains this configurat ion info rm ati on :
•Enabling DVMRP Unicast Routing, page 24-50
•Rejecting a DVMRP Nonpruning Neighbor, page 24-51
•Controlling Route Exchanges, page 24-53
For information on basic DVMRP features, see the “Configuring Basic DVMRP Interoperability
Features” section on page 24-43.

Enabling DVMRP Unicast Routing

Because multicast routing and unicast routing require separate topologies, PIM must follow the
multicast topology to build loopless distribution trees. Using DVMRP unicas t r outing , Cisco rout ers,
multilayer switches, and mrouted-based machines exchange DVMRP unicast routes, to which PIM can
then reverse-path forward.
Cisco devices do not perform DVMRP multicast routing among each other, but they can exchange
DVMRP routes. The DVMRP routes provide a multicast topology tha t m ig ht d iffer f rom th e unic ast
topology. This allows PIM to run over the multicast topology, thereby allowing sparse-mode PIM over
the MBONE topology.
When DVMRP unicast routing is enabled, the router or switch caches routes learned in DVMRP report
messages in a DVMRP routing table. When PIM is running, these routes might be prefe rred over routes
in the unicast routing table, allowing PIM to run on the MBONE topology when it is different from the
unicast topology.
DVMRP unicast routing can run on all interfaces. For DVMRP tunnels, it uses DVMRP multicast
routing. This feature does not enable DVMRP multicast routing among Cisco routers and multilayer
switches. However, if there is a DVMRP-capable multicast router , the Cisco dev ice can do PIM/DVMRP
multicast routing.
Beginning in privileged EXEC mode, follow these steps to enable DVMRP unicast routing:
To disable this feature, use the no ip dvmrp unicast-routing interface configuration command.
Command Purpose
Step1 configure terminal Enter global configuration mode.
Step2 interface interface-id Enter interface configuration mode, and specify the interface that is
connected to the DVMRP router.
Step3 ip dvmrp unicast-routing Enable DVMRP unicast routing (to send and receive DVM RP r oute s).
This feature is disabled by default.
Step4 end Return to privileged EXEC mode.
Step5 show running-config Verify your entries.
Step6 copy running-config startup-config (Optional) Save your entries in the configuration file.