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Catalyst 3750-X and 3560-X Switch Software Configuration Guide
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Chapter 48 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 gigabitethernet1/0/1
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 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 enables 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 RPF calculation. This behavior enables 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 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.