Building BGP Neighbor Relationships
BGP neighbors form a TCP connection with each neighbor, sending BGP messages over the connections—culminating in BGP Update messages that contain the routing information. Each router explicitly configures its neighbors’ IP addresses, using these definitions to tell a router with which IP addresses to attempt a TCP connection. Also, if a router receives a TCP connection request (to BGP port 179) from a source IP address that is not configured as a BGP neighbor, the router rejects the request.
After the TCP connection is established, BGP begins with BGP Open messages. Once a pair of BGP Open messages has been exchanged, the neighbors have reached the established state, which is the stable state of two working BGP peers. At this point, BGP Update messages can be exchanged.
This section examines many of the details about protocols and configuration for BGP neighbor formation. If you are already familiar with BGP, Table 12-2 summarizes some of the key facts found in this section.
Table 12-2 BGP Neighbor Summary Table
* Cisco changed the IOS default for BGP auto-summary to be disabled as of Cisco IOS Software Release 12.3.
After the TCP connection is established, BGP begins with BGP Open messages. Once a pair of BGP Open messages has been exchanged, the neighbors have reached the established state, which is the stable state of two working BGP peers. At this point, BGP Update messages can be exchanged.
This section examines many of the details about protocols and configuration for BGP neighbor formation. If you are already familiar with BGP, Table 12-2 summarizes some of the key facts found in this section.
Table 12-2 BGP Neighbor Summary Table
* Cisco changed the IOS default for BGP auto-summary to be disabled as of Cisco IOS Software Release 12.3.
