Redistribution Techniques

Redistribution is technique using which the boundary routers connecting different routing domains can exchange and advertise routing information. There are 2 methods of route redistribution:

  • One way redistribution: This method is also called one sided redistribution. In this method, a default route is propagated into one routing protocol  and on the other side, it redistributes only the networks learned from that routing protocol into the other routing protocol.
  • Two way redistribution: In this method we have to redistribute all routes between the two routing protocols.
One Way Redistribution Config Example:

In above topology, R2 and R3 are running RIPv2 and no routing protocol is running on R1. So in order to complete the routing, we have to put a static route on R2 for R1's Loopback0 subnet and we have redistributed that subnet in RIP.

R2(config)#ip route

R2(config)#router rip
R2(config-router)#redistribute static metric 3

Kindly also note that we should be careful our choice of configuring static or default route on a non stub router such as R2. Any incorrect default routing can lead to network issues.My recommendation is to use static routing. In order to avoid configuring multiple static routes on R2 for R1's prefixes, we can try to summarize the prefixes where possible.

Two Way Redistribution Config Example:

In above topology, R1 is OSPF domain and R3 is in RIP domain.  R2 is a boundary router running both OSPF and RIP. So in order to exchange the routes between 2 domains, we need to do a two way redistribution of routes on R2 using below config:

R2(config)#router ospf 1
R2(config-router)#redistribute rip subnets

R2(config-router)#router rip
R2(config-router)#redistribute ospf 1 metric 3

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