Cisco IOS Cookbook, 2nd Edition

Routing Multicast Traffic with DVMRP

Problem

You want to route multicast traffic by using the DVMRP protocol.

Solution

Cisco routers support DVMRP only as a gateway to PIM. So the configuration is remarkably similar to the PIM configuration. The key difference is in the ip dvmrp unicast-routing command, which tells the router to use the DVMRP multicast routing table instead of the usual PIM choice of the unicast routing table:

Router1#configure terminal 
Enter configuration commands, one per line.  End with CNTL/Z.
Router1(config)#ip multicast-routing
Router1(config)#interface FastEthernet0/0
Router1(config-if)#ip pim sparse-dense-mode
Router1(config-if)#ip dvmrp unicast-routing
Router1(config-if)#ip dvmrp summary-address 192.168.0.0 255.255.0.0
Router1(config-if)#end
Router1#

Discussion

Before saying anything else, we will stress once again that DVMRP is not our first choice for a multicast routing protocol. PIM-DM is simpler to implement and more efficient with router resources if you want a dense-mode protocol. And PIM-SM scales much better in larger networks or when there are many groups. In fact, Cisco routers do not provide a full implementation of DVMRP. They can take part in DVMRP neighbor discovery and route exchange, but internally the multicast processing is done using PIM. However, you can configure PIM to use the DVMRP routing table, which is what this recipe actually does.

DVMRP is defined in RFC 1075, and was the first widely implemented multicast routing protocol, forming ...