You want to use IS-IS on a GRE interface where the underlying Layer 3 MTU is 1500. Which
statement is correct?

A.
IS-IS can be used because every IS-IS interface must be capable of transmitting packets at
least as large as 1476 bytes, and the GRE header is 24 bytes.

B.
IS-IS cannot be used because the IS-IS hello is not allowed to be fragmented and has the DF
bit set.

C.
IS-IS can be used, but the networking device directly attached to the circuit must be capable of
fragmentation.

D.
IS-IS cannot be used, but the router can enable a GRE key that serves the same function as
IS-IS.

Explanation: