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Catalyst 3550 Multilayer Switch Software Configuration Guide
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Chapter 34 Configuring IP Multicast Routing
Configuring Basic DVMRP Interoperability Features
This example shows how to configure DVMRP interoperability when the PIM device and the DVMRP
router are on the same network segment. In this example, access list 1 advertises the networks
(198.92.35.0, 198.92.36.0, 198.92.37.0, 131.108.0.0, and 150.136.0.0) to the DVMRP router, and access
list 2 prevents all other networks from being advertised (ip dvmrp metric 0 interface configuration
command).
Switch(config-if)# interface gigabitethernet0/1
Switch(config-if)# ip address 131.119.244.244 255.255.255.0
Switch(config-if)# ip pim dense-mode
Switch(config-if)# ip dvmrp metric 1 list 1
Switch(config-if)# ip dvmrp metric 0 list 2
Switch(config-if)# exit
Switch(config)# access-list 1 permit 198.92.35.0 0.0.0.255
Switch(config)# access-list 1 permit 198.92.36.0 0.0.0.255
Switch(config)# access-list 1 permit 198.92.37.0 0.0.0.255
Switch(config)# access-list 1 permit 131.108.0.0 0.0.255.255
Switch(config)# access-list 1 permit 150.136.0.0 0.0.255.255
Switch(config)# access-list 1 deny 0.0.0.0 255.255.255.255
Switch(config)# access-list 2 permit 0.0.0.0 255.255.255.255
Configuring a DVMRP Tunnel
The Cisco IOS software supports DVMRP tunnels to the MBONE. You can configure a DVMRP tunnel
on a router or multilayer switch if the other end is running DVMRP. The software then sends and receives
multicast packets through the tunnel. This strategy allows a PIM domain to connect to the DVMRP router
when all routers on the path do not support multicast routing. You cannot configure a DVMRP tunnel
between two routers.
When a Cisco router or multilayer switch runs DVMRP through a tunnel, it advertises sources in
DVMRP report messages, much as it does on real networks. The software also caches DVMRP report
messages it receives and uses them in its Reverse Path Forwarding (RPF) calculation. This behavior
allows the software to forward multicast packets received through the tunnel.
When you configure a DVMRP tunnel, you should assign an IP address to a tunnel in these cases:
• To send IP packets through the tunnel
• To configure the Cisco IOS software to perform DVMRP summarization
The software does not advertise subnets through the tunnel if the tunnel has a different network number
from the subnet. In this case, the software advertises only the network number through the tunnel.
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