# Configuring DVMRP Summary Addresses

You can configure an interface to advertise a summary address with a known metric rather than a more specific route. DVMRP advertises the summary address if the DVMRP routing table contains a more specific route that matches the address and mask of the summary address.

If you want to advertise all routes rather than a summary, disable automatic summarization on the interface (no ip dvmrp auto-summary). By default, the router automatically summarizes DVMRP routes. DVMRP automatic summarization maps a unicast subnet route to a classful network number route when the subnet has a different network number from the IP address of the interface (or tunnel) over which the advertisement travels. If the interface is unnumbered, the router compares the network number of the numbered interface to the IP address to which the unnumbered interface points.

If you configure a summary address on an interface and do not disable automatic summarization, the interface advertises the least-specific address.

ip dvmrp auto-summary

- Use to reenable the router to summarize routes automatically for this interface. By default, automatic summarization is enabled.
- Example
  host1:boston(config-if)#ip dvmrp auto-summary
- Use the no version to disable automatic summarization for this interface.
- See ip dvmrp auto-summary.

ip dvmrp summary-address

- Use to advertise DVMRP summary addresses on an interface. By default, an interface advertises only summary addresses generated by automatic summarization.
- If you configure multiple overlapping summary addresses on an interface, the one with the shortest mask takes preference.
- Use the metric keyword to specify a DVMRP metric (hop count); the default metric value is 1.
- Example
  host1:boston(config-if)#ip dvmrp summary-address 192.48.1.2 255.255.255.0 metric 1
- Use the no version to stop advertising a summary address on the interface.
- See ip dvmrp summary-address.