Which command makes a loopback address the source address for EBGP neighbor adjacency?

The command that sets the loopback address as the source address for EBGP neighbor adjacency is "neighbor update-source ". This command allows you to specify an alternative source interface or IP address for the BGP session instead of using the IP address of the physical interface that is most commonly used. By configuring this, the loopback interface, which is typically assigned a stable IP address, can be used as the source, improving stability and reliability in BGP deployments.

Utilizing a loopback as the source IP is essential, especially in scenarios where the underlying physical interface might change due to link failures or maintenance. The loopback interface remains up as long as the router itself is operational, ensuring that BGP sessions remain established regardless of the state of physical links.

The other options presented do not facilitate the configuration of a loopback address as the EBGP source address. The command related to configuring the BGP neighbor and specifying the remote AS does not address the source IP configuration. The commands "config t" and "exit" are related to entering configuration mode and exiting from it, respectively, but do not impact the establishment of a BGP adjacency using a loopback address.