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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