Which command defines a peer router and activates a BGP session?

• A. Neighbor ip-address remote-as autonomous-system router config command
• B. Neighbor update-source
• C. Network command
• D. Route-map set

Answer: (A)

BGP peering is formed by telling your router which neighbor to connect to and what AS that neighbor belongs to. The command that does this directly defines the peer by its IP address and specifies the remote ASN, which is what allows the TCP session to be established and the BGP session to begin. In other words, you declare who you want to peer with and what AS they’re in, and the router uses that to initiate and manage the session.

Other options have different roles: updating the source IP used for the BGP connection, which is needed in certain peering setups (like when peering to a loopback); advertising networks into BGP so they are learned by others; and applying policy to BGP routes with a route-map. None of these define the peer or trigger the initial BGP peering in the same direct way.