In BGP, what is the difference between the neighbor command and the network command?

• A. The network command tells what to advertise.
• B. The network command defines the next-hop.
• C. The neighbor command tells BGP where to advertise; the network command tells what to advertise.
• D. They are interchangeable.

Answer: (C)

In BGP, you separate who you peer with from what you advertise. The neighbor command defines the BGP peer: it specifies the router (and optionally the remote AS, update source, etc.) with which you want to establish a BGP session. Without a neighbor, there’s no path to exchange routes.

The network command, on the other hand, determines which networks from your own routing table you will advertise into BGP. You list networks (with optional masks), and BGP originates those routes into the BGP process so they can be shared with all established neighbors. Importantly, those networks must exist in the local routing table to be advertised.

So the neighbor command establishes where to send updates (which peer to talk to), while the network command decides what networks to advertise.