Enabling Dvmrp Unicast Routing; Rejecting A Dvmrp Nonpruning Neighbor - Cisco WS-C3750-48PS-S Software Configuration Manual

Chapter 36 Configuring IP Multicast Routing

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 unicast routing, Cisco routers,
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 that might differ from the unicast
topology. This enables PIM to run over the multicast topology, thereby enabling 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 preferred over routes
in the unicast routing table, enabling 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 device can do PIM/DVMRP
multicast routing.
Beginning in privileged EXEC mode, follow these steps to enable DVMRP unicast routing. This
procedure is optional.
Command
Step 1
configure terminal
Step 2 interface interface-id
Step 3 ip dvmrp unicast-routing
Step 4 end
Step 5
show running-config
Step 6 copy running-config startup-config
To disable this feature, use the no ip dvmrp unicast-routing interface configuration command.

Rejecting a DVMRP Nonpruning Neighbor

By default, Cisco devices accept all DVMRP neighbors as peers, regardless of their DVMRP capability.
However, some non-Cisco devices run old versions of DVMRP that cannot prune, so they continuously
receive forwarded packets, wasting bandwidth.
78-16180-02
Configuring Advanced DVMRP Interoperability Features
Purpose
Enter global configuration mode.
Specify the interface that is connected to the DVMRP router, and enter
interface configuration mode.
Enable DVMRP unicast routing (to send and receive DVMRP routes).
This feature is disabled by default.
Return to privileged EXEC mode.
Verify your entries.
(Optional) Save your entries in the configuration file.
Figure 36-6
Catalyst 3750 Switch Software Configuration Guide
shows this scenario.
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