SPF side, as it was redistributed into EIGRP on R2: R3#sho ip route [text removed] Gateway of last resort is not set 50.0.0.0/24 is subnetted, 1 subnets 50.50.50.0 is directly connected, Loopback0 20.0.0.0/24 is subnetted, 1 subnets 20.20.20.0 is directly connected, Ethernet1/0 10.0.0.0/24 is subnetted, 1 subnets D EX 10.10.10.0 [170/537600] via 20.20.20.1, 00:00:15, Ethernet1/0 The key to this example lies in the fact that EIGRP has a higher administrative distance for external routes (170) than it does for internal routes (90). OSPF only has one ad- ministrative distance for all routes (110). This type of problem can cause no end of headaches in a production environment. If you don't have experience using redistribution in complex environments, this is a very easy mistake to make. Symptoms of the problem include routes pointing to places you don'texpect. Look carefully at the design and follow the route back to its source to see where the problem starts. In networks where you're redistributing between different Chapter 11: Redistribution autonomous systems using the same routing protocol, you may see routes flip-flop back and forth between sources. This behavior can be caused by each autonomous system reporting the same metric, in which case the router will update its routing table each time it receives an update. In the present example, one way to resolve the problem is to stop redistributing the connected route and include the interface into EIGRP with the network command. Using this approach, the route becomes an internal route with an administrative dis- tance of 90, which is more desirable than OSPF's administrative distance of 110. Limiting Redistribution When designing complex networks with multiple redistribution points, you must somehow limit redistribution SO that loops are prevented. Next I'll show you my method of choice, which involves tagging routes and filtering with route maps. Route Tags Many routing protocols-for example, EIGRP, OSPF, and RIPv2 (but not RIPv1)- allow you tag routes with values