Router R1 is a BGP speaker with one peering neighbor over link "A".

D (Fate sharing):Fate sharing refers to a design where multiple dependent states fail together (i.e., when physical link fails, BGP session and its routes fail too).

Other options explained:

A: Fault isolation refers to containing failures, not dependent failure.

B: Resiliency is the ability to recover, not simultaneous failure.

C: Redundancy would prevent total loss if implemented.