ICMP is a low-level Internet operation message protocol that is used between gateways and hosts. It uses several message codes. What would a code 3 mean?

A.
Communication administratively prohibited

B.
IP header was bad

C.
TTL expired

D.
Host unknown, network unreachable

Explanation:
A listing of ICMP messages includes:
0 Echo reply (ping reply)
3 Delivery failure (host unknown, network unreachable)
4 Source quench
8 Echo request (ping request)
11 Time to live (TTL) expired (used by traceroute)
12 IP header was bad
13 Communication administratively prohibited