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Catalyst 3750 SwitchSoftware Configuration Guide
OL-8550-09
Chapter46 Configuring IP Multicast Routing
Configuring Advanced DVMRP Interoperability Features
Disabling DVMRP Autosummarization
By default, the software automatically performs some level of DVMRP summarization. Disable this
function if you want to advertise all routes, not just a summary. In some special cases, you can use the
neighboring DVMRP router with all subnet information to better control the flow of multicast traffic in
the DVMRP network. One such case might occur if the PIM network is connected to the DVMRP cloud
at several points and more specific (unsummarized) routes are being injected into the DVMRP network
to advertise better paths to individual subnets inside the PIM cloud.
If you configure the ip dvmrp summary-address interface configuration command and did not
configure no ip dvmrp auto-summary, you get both custom and autosummaries.
Beginning in privileged EXEC mode, follow these steps to disable DVMRP autosummarization. This
procedure is optional.
To re-enable auto summarization, use the ip dvmrp auto-summary interface configuration command.
Adding a Metric Offset to the DVMRP Route
By default, the switch increments by one the metric (hop count) of a DVMRP route advertised in
incoming DVMRP reports. You can change the metric if you want to favor or not favor a certain route.
For example, a route is learned by multilayer switch A, and the same route is learned by multilayer
switch B with a higher metric. If you want to use the path through switch B because it is a faster path,
you can apply a metric offset to the route learned by switch A to make it larger than the metric learned
by switch B, and you can choose the path through switch B.
Command Purpose
Step1 configure terminal Enter global configuration mode.
Step2 interface interface-id Specify the interface connected to the DVMRP router, and enter
interface configuration mode.
Step3 no ip dvmrp auto-summary Disable DVMRP autosummarization.
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.