What is the problem?

A GRE tunnel is established between two routers. When a user on one end sends traffic with a large packet size to a user on the remote end, the packet never arrives. However, the problem does not exist for smaller packets. What is the problem?

A.
The tunnel is down on the remote end.

B.
The don’t-fragment bit is set on the traffic.

C.
GRE tunnels do not support IP traffic.

D.
No dynamic routing protocol exists to handle the traffic.