Route Redistribution

It is important to consider the following rules when redistributing between IP routing protocols:

■ If more than one routing protocol is running on a router, the routing table process will place
the route with the best administrative distance into the routing table.
■ Routing protocols can only redistribute routes they know. Thus, if RIP is being redistributed
into EIGRP, the routing table must have an entry for the RIP network.
■ When a route is redistributed, it inherits the default administrative distance of the new routing
protocol.
■ Redistributed routes are called external. External routes in EIGRP are given a different
(higher) AD, while OSPF tracks the route as external and prefers internal routes.

Potential problems:

■ Routing loops because routers send routing information received from one autonomous 

system back into the same autonomous system.

■ Suboptimal routing decisions are made because of the difference in routing metrics. 

■ The convergence time increases because of the different technologies involved. If the routing 

protocols converge at different rates, this might result in timeouts and the temporary loss of 

networks.

■ The decision-making process and the information sent within the protocols might be 

incompatible and not easily exchanged, leading to errors and complex configuration.

Control Methods:

■ Passive interfaces

■ Static routes

■ Default routes

■ The null interface

■ Distribute lists

■ Route maps