What TCP port does BGP use for establishing a session?

Border Gateway Protocol (BGP) uses TCP port 179 to establish sessions between BGP peers. This is a well-defined standard within the protocol specifications, and all BGP implementations are designed to use this specific port for communication. The choice of port 179 is crucial because it allows for reliable transmission of routing information between different autonomous systems on the internet.

Using TCP ensures that BGP can handle issues such as packet loss and retransmission, which are imperative for maintaining consistent routing information. By establishing connections on this designated port, routers can efficiently manage and exchange routing updates, which is essential for the dynamic routing process across diverse networks. This port assignment is part of the Internet Assigned Numbers Authority (IANA) Service Name and Transport Protocol Port Number Registry, reflecting the standardization and widespread adoption of BGP in internet routing practices.