Cisco Systems 78-11741-02 manual Limiting the Number of Dvmrp Routes Advertised, IPC-541

Configuring DVMRP Interoperability

Advanced DVMRP Interoperability Configuration Task List

When DVMRP unicast routing is enabled, the router caches routes learned in DVMRP report messages in a DVMRP routing table. PIM prefers DVMRP routes to unicast routes by default, but that preference can be configured.

DVMRP unicast routing can run on all interfaces, including generic routing encapsulation (GRE) tunnels. On DVMRP tunnels, it runs by virtue of DVMRP multicast routing. This feature does not enable DVMRP multicast routing among Cisco routers. However, if there is a DVMRP-capable multicast router, the Cisco router will do PIM/DVMRP multicast routing interaction.

To enable DVMRP unicast routing, use the following command in interface configuration mode:

Command	Purpose
Router(config-if)#ip dvmrp unicast-routing	Enables DVMRP unicast routing.

Limiting the Number of DVMRP Routes Advertised

By default, only 7000 DVMRP routes will be advertised over an interface enabled to run DVMRP (that is, a DVMRP tunnel, an interface where a DVMRP neighbor has been discovered, or an interface configured to run the ip dvmrp unicast-routinginterface configuration command).

To change this limit, use the following command in global configuration mode:

Command	Purpose
Router(config)# ip dvmrp route-limit count	Changes the number of DVMRP routes advertised over an interface
	enabled to run DVMRP.

Changing the DVMRP Route Threshold

By default, 10,000 DVMRP routes may be received per interface within a 1-minute interval. When that rate is exceeded, a syslog message is issued, warning that a route surge might be occurring. The warning is typically used to quickly detect when routers have been misconfigured to inject a large number of routes into the MBONE.

To change the threshold number of routes that trigger the warning, use the following command in global configuration mode:

Command	Purpose
Router(config)# ip dvmrp routehog-notification	Configures the number of routes that trigger a syslog message.
route-count

Use the show ip igmp interface EXEC command to display a running count of routes. When the count is exceeded, “*** ALERT ***” is appended to the line.

Configuring a DVMRP Summary Address

You can customize the summarization of DVMRP routes if the default classful automatic summarization does not suit your needs. To summarize such routes, specify a summary address by using the following command in interface configuration mode:

Cisco IOS IP Configuration Guide

IPC-541