What does ICMP Type 3 Code 13 indicate?

• A. Administratively Blocked
• B. Host Unreachable
• C. Protocol Unreachable
• D. Port Unreachable

Answer: (A)

ICMP Type 3 messages convey that the destination is unreachable, and the code specifies the reason. Code 13 means the traffic is administratively blocked or prohibited, typically by a firewall or policy setting. This is a policy-based denial rather than a failure of the destination host or a missing/unsupported service. So the packet can exist and be reachable, but the router or gateway is intentionally blocking it for administrative reasons.

That’s why Administratively Blocked is the best match. Other codes refer to different, non-policy reasons: for example, a reachable host that can’t be reached for routing reasons, or an unreachable protocol or port on the destination, which are not what code 13 indicates.