To establish point-to-point connections between peer ASs, you configure a BGP session on each interface of a point-to-point link. Figure 31 shows an example of a BGP peering session.
Figure 31: BGP Peering Session

In Figure 31, router A is a gateway router for AS 3, and router B is a gateway router for AS 10. For traffic internal to either AS, an IGP (OSPF, for instance) is used. To route traffic between peer ASs, a BGP session is used.