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Configuring On-Demand Routing
IPC-197
Cisco IOS IP Configuration Guide
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:
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:
Command Purpose
Router(config-router)# distribute-list access-list-number |
access-list-name | prefix list-name {in | out} [interface-type
interface-number]
Filters ODR information on the hub
router.