The exhibit shows the configuration of BFD liveness detection for BGP at the global level, which

applies to all BGP neighbors by default1. However, this configuration does not specify the session

mode, which determines whether BFD uses single-hop or multihop mode to communicate with a

neighbor2.

For single-hop BGP neighbors, which are directly connected on the same subnet, the session mode

can be either automatic or single-hop. For multihop BGP neighbors, which are not directly connected

and require multiple hops to reach, the session mode must be multihop2.

Since

your BGP

neighbors

are

in different countries,

they

are

likely

to be

multihop

neighbors. Therefore, you need to configure the session mode as multihop for each neighbor

individually at the [edit protocols bgp group group-name neighbor address bfd-liveness-detection]

hierarchy level2. For example:

protocols { bgp { group usa { neighbor 192.0.2.1 { bfd-liveness-detection { session-mode multihop; } }

} group france { neighbor 198.51.100.1 { bfd-liveness-detection { session-mode multihop; } } } } }

If you do not configure the session mode for multihop neighbors, BFD will use the default mode of

automatic, which will try to use single-hop mode and fail to establish a BFD session with the remote

neighbor2. This will prevent BGP from using BFD to detect liveliness and failover.

Therefore, the answer B is correct, as you need to configure the BFD liveness detection on the BGP

neighbor level with the appropriate session mode for multihop neighbors.