What is route redistribution and why to use it?
Route redistribution is the process of sharing routes from one routing protocol and distribute them into another. By default, routers only advertise and share routes with other routers running the same protocol. As such if one router is configured for OSPF and the other EIGRP and need to share routes, by default, they will not share routing information. To accommodate sharing routes with other routing protocols route redistribution is required.
In the network below there are a total of five routers. Three routers are configured for EIGRP and the others are configured for BGP and OSPF, respectively. In this example EIGRP is redistributed into BGP and OSPF, and BGP and OSPF are redistributed into EIGRP. The most interesting configurations will occur on R3 but we will use R4 and R5 to verify all of the routes are properly being redistributed. The reason why we are using R4 and R5 to verify routes is to also confirm the routes are labeled as external. An external route is defined as any route that is not within the primary routing protocol.
Verify the configuration
Now that the configuration is finished lets verify our neighbors and routes. Using the show ip bgp summary, show ip eigrp neighbors, show ip ospf neighbor, and show ip route commands you can verify the remote routers to which your router has formed an adjacency and verify the expected routes are being advertised.We will confirm our neighbors using R3 but we will use R4 and R5 to verify all of the routes are properly being redistributed. Use the ping command to verify connectivity.
