Which protocol and the port number does BGP use for neighborship?

Border Gateway Protocol (BGP) uses TCP as its transport protocol for establishing neighborships. Specifically, BGP operates over TCP port 179. Here’s a breakdown:

• Protocol: TCP (Transmission Control Protocol)
• Port Number: 179

Details

• TCP: BGP uses TCP to ensure reliable delivery of routing updates and to maintain the connection between BGP peers. TCP's reliability features (such as error correction and packet ordering) are essential for BGP's operation.
• Port 179: This is the standard port number assigned to BGP for establishing and maintaining BGP sessions between routers.

BGP Neighborship Establishment Process

1. Open Message: When a BGP session is initiated, a router sends an OPEN message to its BGP neighbor over TCP port 179 to start the session.
2. Keepalive Message: After the initial connection is established, routers exchange KEEPALIVE messages periodically to maintain the session.
3. Update Message: BGP routers exchange UPDATE messages to share routing information.
4. Notification Message: If there are errors or issues with the BGP session, routers exchange NOTIFICATION messages to terminate the session.

This use of TCP and port 179 ensures a reliable and orderly exchange of routing information between BGP peers.