Cisco Systems 78-11741-02 manual Disabling Dvmrp Automatic summarization, IPC-542

Configuring DVMRP Interoperability

Advanced DVMRP Interoperability Configuration Task List

Command	Purpose
Router(config-if)#ip dvmrp summary-address	Specifies a DVMRP summary address.
summary-address mask [metric value]

Note At least one, more-specific route must be present in the unicast routing table before a configured summary address will be advertised.

Disabling DVMRP Automatic summarization

By default, the Cisco IOS software performs some level of DVMRP summarization automatically. Disable this function if you want to advertise all routes, not just a summary. If you configure the

ip dvmrp summary-addressinterface configuration command and did not configure the no ip dvmrp auto-summarycommand, you get both custom and automatic summaries.

To disable DVMRP automatic summarization, use the following command in interface configuration mode:

Command	Purpose
Router(config-if)#no ip dvmrp auto-summary	Disables DVMRP automatic summarization.

Adding a Metric Offset to the DVMRP Route

By default, the router increments by 1 the metric 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. The DVMRP metric is a hop count. Therefore, a very slow serial line of one hop is preferred over a route that is two hops over FDDI or another fast medium.

For example, perhaps a route is learned by Router A and the same route is learned by Router B with a higher metric. If you want to use the path through Router B because it is a faster path, you can apply a metric offset to the route learned by Router A to make it larger than the metric learned by Router B, allowing you to choose the path through Router B.

To change the default metric, use the following command in interface configuration mode:

Command	Purpose
Router(config-if)#ip dvmrp metric-offset [in	Changes the metric added to DVMRP routes advertised in incoming
out] increment	reports.

Similar to the metric keyword in mrouted configuration files, the following is true when using the ip dvmrp metric-offsetinterface configuration command:

•When you specify the in keywordor no keyword, the increment value is added to incoming DVMRP reports and is reported in mrinfo replies. The default value for the in keyword is 1.

•When you specify the out keyword, the increment is added to outgoing DVMRP reports for routes from the DVMRP routing table. The default value for the out keyword is 0.

Cisco IOS IP Configuration Guide

IPC-542