On Demand Routing (ODR)

Lessons Learned:

Not used as much anymore but is still is viable on smaller networks. Basically Dynamic routing rides on top of CDP, any originally designed for Hub and spoke networks / X.25 / Hub and spoke frame networks. Where the spokes of the network have one physical link to the to the hub. So the Spokes really only need to a default route. The hub would need to know all the stubs or spoke networks that are being advertised up to the Hubs.

On the Stub routers you cannot have any other routing protocols. Ex if you configure RIP or OSPF, etc – it automatically disables the advertisements of your networks inside of CDP. The IP Routing process must be on but all other routing protocols must be off.

On the Hub Router – you just need to configure “Router ODR”.

 

ODR:

-Uses CDP to advertise directly connected networks to the hub router.

--Hub router advertises default route to “stub” router via CDP.

Configuration on Hub

-# router odr

Note: when configuring ODR the only real prerequisite is that CDP be running on all the routers.

Verifications for CDP:

# Sh cdp neighbors

# sh cdp Interfaces

Note: On most frame-relay interfaces CDP is off by default. CDP will run on the Sub-Interface but it will not run on the main interface.

Once ODR is configured. you'll notice the route in the tabel with a lowercase "o".

o* 0.0.0.0/0 [160/1] via 10.1.1.1, 00:00:35, Serial0/0
R3#

The spoke's will not learn about the subnets from the hub, just the default route.

Gateway of last resort is 10.1.1.1 to network 0.0.0.0

o* 0.0.0.0/0 [160/1] via 10.1.1.1, 00:00:57, Serial0/0

The spokes should now be able tp reach all subnets that the Hub know's about.

Note: ODR has an administrative distance of 160 by default. This means it would less preferrred by any other dynamic protocols except for External BGP and Internal BGP.

 

Note: to change the convergence of ODR - you'll need to change the timers from CDP because this is how ODR gets it's updates.