Once ODR is enabled on a hub router, the hub router begins installing stub network routes in the IP forwarding table. The hub router also can be configured to redistribute these routes into any configured dynamic IP routing protocols.

To enable ODR on a hub router, perform the steps in this task.

ODR uses Cisco Discovery Protocol to carry minimal routing information between the hub and stub routers, allowing stub routers to send IP prefixes to the hub router. Perform the steps in this task to disable the propagation of ODR stub routing information by disabling CDP.

On stub routers that support the ODR feature, the stub router advertises IP prefixes corresponding to the IP networks configured on all directly connected interfaces. Perform the steps in this task to disable the propagation of ODR stub routing information on a specified interface.

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

In this example, the ACL filters the following Class A network prefixes:

access-list 101 permit 10.48.0.3
access-list 101 deny 10.48.0.0  0.0.255.255 
access-list 101 permit 10.0.0.0  0.255.255.255 
interface gigabitethernet 0/0/0
 ip access-group 2 in

To filter ODR information, perform the steps in this task.

By default, Cisco Discovery Protocol sends updates every 60 seconds. This update interval may not be frequent enough to provide fast 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 Cisco Discovery Protocol 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 Cisco Discovery Protocol update interval. Configuration changes made to either the Cisco Discovery Protocol or ODR timers should be reflected through changes made to both.

To reconfigure Cisco Discovery Protocol or ODR timers, perform the steps in this task.

For interfaces that specify dialer mappings, Cisco Discovery Protocol packets will make use of dialer map configuration statements that pertain to the IP protocol. Because Cisco Discovery Protocol packets are always broadcast packets, these dialer map statements must handle broadcast packets, typically through use of the dialer map command with the broadcast keyword. The dialer string command in interface configuration mode may also be used.

On dial-on-demand (DDR) routing interfaces, certain kinds of packets can be classified as interesting. These interesting packets can cause a DDR connection to be made or cause the idle timer of a DDR interface to be reset. For the purposes of DDR classification, Cisco Discovery Protocol packets are considered uninteresting. This classification occurs even while Cisco Discovery Protocol is making use of dialer map statements for IP, where IP packets are classified as interesting.

The following task describes how to use dialer map statements to direct Cisco Discovery Protocol broadcast packets.

or

dialer string dial-string [: isdn-subaddress]

The following example shows how to enable ODR on a Cisco router and enable filtering of ODR information. The configuration example for filtering ODR information causes the hub router to accept only advertisements for IP prefixes about (or subnets of) the Class C network 192.168.1.0:

Router(config)# access-list 101 permit ip host 10.0.0.1 192.168.1.0 0.0.0.255
 
Router(config)# access-list 101 permit ip 10.0.10.2 255.0.0.0 192.168.2.0 0.0.0.255 
Router(config)# router odr 
Router(config-router)# distribute-list 101 in 
Router(config-router)# end 

The following example shows how to disable ODR on an interface:

Router# configure terminal
Router(config)# interface GigabitEthernet 0/0/0

Router(config-if)# no cdp enable