Monday, March 16, 2009

BGP Session Establishment

BGP is a normal TCP application, which means that a TCP client 
initiates the session to the TCP server with a SYN packet going 
to the well known port of 179. If the BGP server is configured to 
accept the session, a reply with SYN/ACK comes from port 179, 
going to the high port that is negotiated between them. In the 
case that both BGP peers attempt to establish the connection 
at the sametime, RFC 4271 (A Border Gateway Protocol 4) defines
a “BGP Connection Collision Detection” mechanism, in which 
essentially the session originated from the device with the higher
BGP router-id is maintained, and the secondary session is dropped.

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