The show ip route command shows you which BGP routes have made it to the IP routing table. BGP is NOT used to make forwarding decisions on data, it is used to learn the single best path to a destination network. To do this, BGP listens for routes and advertises the best routes it knows. BGP also places the best route it knows for each destination (prefix) into the IP routing table. A Cisco router uses the Best Path Selection Algorithm to select the single best route to a destination and then inserts it into the IP routing table.

To check a router's IP routing table for a given destination (such as Yahoo), simply use the show ip route command:

route-server>show ip route 216.109.127.30
   Routing entry for 216.109.112.0/20, supernet
 Known via "bgp 65000", distance 20, metric 0
 Tag 7018, type external
 Last update from 12.123.9.241 1d17h ago
 Routing Descriptor Blocks:
 * 12.123.9.241, from 12.123.9.241, 1d17h ago
 Route metric is 0, traffic share count is 1
 AS Hops 5
 Route tag 7018

From the above output, the route to Yahoo (216.109.127.30 in this case) is known via an external BGP peer. As this is the ONLY route to the destination, this is the preferred route.

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