On-Demand Routing (ODR)

On Demand Routing uses CDP to advertise the connected IP prefix of the stub router via CDP and transmit to HUB router. The stub router will have a default route installed in its routing table. When configuring ODR, make sure that there is no routing protocol running on the router.

Command to enable ODR.
In global configuration
router odr

Example

R1 is a HUB. R2 and R3 are spoke routers. Note that we do not have any routing process on R3 and R2. R1 only have IP reachability to R2 and R3. Configuration is only done on R1.

Configuration



R1#conf t
Enter configuration commands, one per line.  End with CNTL/Z.
R1(config)#router odr
R1(config)#router odr
R1(config-router)#

Verify Configuration

R1#sh ip route
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
       D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
       E1 - OSPF external type 1, E2 - OSPF external type 2
       i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
       ia - IS-IS inter area, * - candidate default, U - per-user static route
       o - ODR, P - periodic downloaded static route

Gateway of last resort is not set

     1.0.0.0/32 is subnetted, 1 subnets
o       1.1.1.1 [160/1] via 192.168.1.2, 00:00:01, FastEthernet0/0
     2.0.0.0/32 is subnetted, 1 subnets
o       2.2.2.2 [160/1] via 192.168.2.2, 00:00:35, FastEthernet0/1
C    192.168.1.0/24 is directly connected, FastEthernet0/0
C    192.168.2.0/24 is directly connected, FastEthernet0/1
R1#

Spoke Routing table

R2#sh ip route

Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP

       D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area

       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2

       E1 - OSPF external type 1, E2 - OSPF external type 2

       i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2

       ia - IS-IS inter area, * - candidate default, U - per-user static route

       o - ODR, P - periodic downloaded static route

Gateway of last resort is 192.168.2.1 to network 0.0.0.0

     2.0.0.0/32 is subnetted, 1 subnets

C       2.2.2.2 is directly connected, Loopback1

C    192.168.2.0/24 is directly connected, FastEthernet0/0

o*   0.0.0.0/0 [160/1] via 192.168.2.1, 00:00:48, FastEthernet0/0