On Demand Routing
ODR – Do you ever seen ODR words? you may notice it when you issue the command “show ip route”.
ODR – On Demand Routing. Most of Cisco router support it, but Packet tracer doesn’t have any ODR features.
Curios what kind of routing protocol is that? This is dead simple routing protocol. Even more simple than RIP.
ODR is Classless routing protocol (supports VLSM). ODR is considered as a third choice between Static Routing and Dynamic Routing. ODR itself doesn’t fully qualified as a Dynamic routing protocol.
NOTE: In the Cisco routing table, ODR-learned routes are marked with lowercase o character “o”. Don’t be confused with OSPF that using uppercase O.
NOTE : ODR only works in Hub and Spoke Topology. And CDP must be enabled on the router.
And, How it works?
ODR uses proprietary CDP (Cisco Discovery Protocol), as a transport to bring ODR’s information. and ODR uses very minimal router resource.
The spoke Router, is a stub router (spoke is always stub though), will gives the network information to the Hub. And then, every spoke router just using default route pointing to their hub, for communicate with other networks. The Hub router will read the CDP information/networks information from Spoke router, install it on the routing table, and use CDP source address as the next-hop IP to reach the spoke networks.
The Hub router, can redistribute ODR learned routes to another routing protocol such as RIP, EIGRP,OSPF and so on.
ODR does not have any metric calculation, However, the metric in routing table always shown as 1, and the default AD(Administrative Distance) is 160.
Commands for configuring ODR
In the Hub router, use router odr command under global configuration mode
In the spoke router, nothing required to configure. But, you can’t use any routing protocols in the spoke router in order to make ODR working.
Optional Commands to tweaks ODR:
– R(config-router)#timers basic
– R(config)#cdp timer
Thanks for reading!