When is a first-hop redundancy protocol needed in the distribution layer?

A.
when the design implements Layer 2 between the access arid distribution blocks

B.
when multiple vendor devices need to be supported

C.
when preempt tuning of the default gateway is needed

D.
when a robust method of backing up the default gateway is needed

E.
when the design implements Layer 2 between the access switch and the distribution blocks

F.
when the design implements Layer 2 between the access and distribution blocks