Open Shortest Path First (OSPF) routes redistributed into Enhanced Interior Gateway Routing Protocol (EIGRP) and EIGRP routes redistributed into Routing Information Protocol (RIP) are not entered into the routing table by default. EIGRP uses a complex metric based on bandwidth, delay, reliability, and load. Because of its complex metric, EIGRP requires that redistributed routes be assigned a metric before they are entered into the routing table. To assign a default metric for routes redistributed into EIGRP, you should issue the defaultmetric bandwidth delay reliability loading mtu command. To assign a metric to an individual route redistributed into EIGRP, you should issue the redistribute protocol[processid | autonomoussystemnumber] metric bandwidth delay reliability loading mtu command.
If no metric is assigned during redistribution and no default metric is configured for EIGRP, the routes are assigned an infinite metric and are ignored by EIGRP.
RIP uses hop count as a metric. Valid hop count values are from 1 through 15; a value of 16 is considered to be infinite. The hop count metric increases by 1 for each router along the path. Cisco recommends that you set a low value for the hop count metric for redistributed routes. To assign a default metric for routes redistributed into RIP, you should issue the defaultmetric hopcount command. To assign a metric to an individual route redistributed into RIP, you should issue the redistribute protocolhopcount command. If no metric is assigned during redistribution and no default metric is configured for RIP, the routes are assigned an infinite metric and are ignored by RIP.
Border Gateway Protocol (BGP) routes and RIP routes redistributed into OSPF are entered into the routing table as external routes. The default metric that OSPF assigns to redistributed routes is 20? however, BGP is an exception and is assigned a default metric of 1. OSPF uses a cost metric based on the bandwidth of each participating interface. OSPF prefers internal routes with the lowest cost. By default, all routes redistributed into OSPF are designated as Type 2 external (E2) routes. E2 routes have a metric that remains constant throughout the routing domain. Alternatively, routes redistributed into OSPF can be designated as Type 1 external (E1) routes. With E1 routes, the internal cost of the route is added to the initial metric assigned during redistribution.
EIGRP routes redistributed into BGP are entered into the routing table without the metric being changed. BGP uses the EIGRP metric as a multi-exit discriminator (MED). The MED is one of several variables BGP considers before making a path selection. BGP considers weight, local preference, origin, and autonomous system (AS) path length before using the MED for path selection.