CCNP Routing and Switching ROUTE 300-101 Official Cert Guide

BGP Internals and Verifying eBGP Neighbors

Similar to OSPF, the BGP neighbor relationship goes through a series of states over time. Although the Finite State Machine (FSM) for BGP neighbor states has many twists and turns, particularly for handling exceptions, retries, and failures, the overall process works as follows:

Step 1. A router tries to establish a TCP connection with the IP address listed on a neighbor command, using well-known destination port 179.

Step 2. When the three-way TCP connection completes, the router sends its first BGP message, the BGP Open message, which generally performs the same function as the EIGRP and OSPF Hello messages. The Open message contains several BGP parameters, including those that must be verified before ...