In BGP, what does the 'neighbor X remote-as Y' command configure?

• A. The remote AS number for the neighbor
• B. The update source interface
• C. The local router ID
• D. The next-hop setting

Answer: (A)

The key idea is that BGP needs to know the autonomous system of the peer you’re connecting to. The command to configure a neighbor’s AS tells your BGP process which AS the remote router belongs to. This is crucial because it determines the type of peering you have: if the neighbor’s AS is different from yours, you form an external BGP session; if it’s the same, you form an internal BGP session. Knowing the neighbor’s AS also influences how routes are advertised and how AS paths are built.

So, this command is used specifically to declare the remote AS number for that neighbor. The other settings—such as which interface IP is used to establish the BGP TCP session, the local router’s own BGP ID, or how the next-hop is treated—are configured separately and do not define the neighbor’s AS.