Introduction to BGP (4)

1. The BGP table plays a key role in the process of learning using routing information with BGP. A router stores all learned BGP prefixs and PAs in its BGP table. The router will later choose which route for each prefix is the best BGP route . The router can then advertise its BGP table to its neighbors , advertising only the best route for each prefix.

 

2. When a BGP neighborship reaches the Established state , those neighbors begin sending BGP Update messages to each other. The router receiving an Update places those learned prefixs into its BGP table, regardless of whether the route appears to be the best roure. Like EIGRP and OSPF , BGP puts all learned routing information into its table , and then BGP processes all potential routes to choose the best route for each prefix.

　　The BGP table should hold all learned prefixs , from each neighbor , except for any prefixs filtered by an inbound BGP filter.

 

3. Verification Commands for eBGP-Learned Routes

show ip bgp 0.0.0.0 0.0.0.0　　　　List possible default routes

show ip bgp prefix [subnet-mask]　　　　List possible routes,per prefix

show ip bgp neighbor ip-address received-routes　　　　List routes learned from one neighbor,before any inbound filtering is applied

show ip bgp neighbors ip-address routes　　　　List routes learned from a specific neighbor that pass any inbound filters

show ip bgp neighbors ip-address advertised-routes　　　　List routes advertised to a neighbor after applying outbound filtering

show ip bgp summary　　　　List the number of prefix learned per neighbor