Cisco Systems 78-11741-02 Filtering ODR Information, Reconfiguring CDP or ODR Timers, Router

Configuring On-Demand Routing

Filtering ODR Information

The hub router will attempt to populate the IP routing table with ODR routes as they are learned dynamically from stub routers. The IP next hop for these routes is the IP address of the neighboring router as advertised through CDP.

Use IP filtering to limit the network prefixes that the hub router will permit to be learned dynamically through ODR.

To filter ODR information, use the following command in router configuration mode:

Command	Purpose
Router(config-router)# distribute-listaccess-list-number	Filters ODR information on the hub
access-list-name prefix list-name {in out} [interface-type	router.
interface-number]

For example, the following configuration causes the hub router to only accept advertisements for IP prefixes about (or subnets of) the Class C network 1982.168.1.0:

Router(config)# access-list 101 permit ip any 192.168.1.0 0.0.0.255

Router(config)# !

Router(config)# router odr

Router(config)# distribute-list 101 in

Router(config)# end

Redistributing ODR Information into the Dynamic Routing Protocol of the Hub

This task may be performed by using the redistribute router configuration command. The exact syntax depends upon the routing protocol into which ODR is being redistributed.

See the “Redistribute Routing Information” section in the “Configuring IP Routing

Protocol-Independent Features” chapter.

Reconfiguring CDP or ODR Timers

By default, CDP sends updates every 60 seconds. This update interval may not be frequent enough to provide speedy reconvergence of IP routes on the hub router side of the network. A faster reconvergence rate may be necessary if the stub connects to one of several hub routers via asynchronous interfaces such as modem lines.

ODR expects to receive periodic CDP updates containing IP prefix information. When ODR fails to receive such updates for routes that it has installed in the routing table, these ODR routes are first marked invalid and eventually removed from the routing table. (By default, ODR routes are marked invalid after 180 seconds and are removed from the routing table after 240 seconds.) These defaults are based on the default CDP update interval. Configuration changes made to either the CDP or ODR timers should be reflected through changes made to both.

To configure CDP or ODR timers, use the following commands beginning in global configuration mode:

Cisco IOS IP Configuration Guide

IPC-197