Case Study: Troubleshooting BGP Neighbor Relationships
Because BGP is designed as an EGP, rather than an IGP, there isn't much to BGP neighbor relationships. The primary thing to keep in mind is that all communications between BGP peers are based on TCP. So, a valid IP connection must be in place between the peers before a relationship can be established. Take a look at Figure 8-7, which is only three routers, to see what problems are possible.
Figure 8-7. Simple Network with BGP Peers
Begin by looking at what Router A would look like with a good, "up and running" eBGP neighbor relationship with Router B. Issuing show ip bgp neighbor results ...
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