ICMP Type 3 Code 13 Meaning

312-49v10 By islever Editorial Last updated

Network Forensics

Short answer

B ICMP Type 3/Code 13 indicates that communication is administratively prohibited or blocked by a firewall or ACL.

Question

What does ICMP Type 3/Code 13 mean?
  1. Host Unreachable
  2. Administratively Blocked Correct Answer
  3. Port Unreachable
  4. Protocol Unreachable

Key Takeaways

This question tests knowledge of ICMP destination unreachable codes and the common trap of confusing administrative blocks with host or port unreachability.

ICMP Type 3, Code 13 indicates that a packet was administratively prohibited or blocked. This explanation clarifies the specific meaning of this network forensics indicator.

Common mistake: Candidates often mistake Code 13 for Host Unreachable (Code 1) or Port Unreachable (Code 3) due to similar error categories.

Expert Analysis

Why the Answer Is Correct

ICMP Type 3 is designated for 'Destination Unreachable' messages. Within this category, Code 13 specifically signifies 'Communication Administratively Prohibited'. This means the packet was dropped by an intermediate device, such as a firewall or router, due to access control lists (ACLs) or security policies rather than a lack of connectivity.

Why the Other Options Are Wrong

Option A (Host Unreachable) corresponds to ICMP Type 3/Code 1, which occurs when a router cannot find a route to the destination network. Option C (Port Unreachable) is ICMP Type 3/Code 3, indicating no application is listening on the target port. Option D (Protocol Unreachable) is ICMP Type 3/Code 2, meaning the IP protocol specified in the header is not supported by the destination host.

Community Comment Notes

The community consensus strongly supports Option B. As user 044f354 noted, "Type 3/Code 13 means the packet was administratively filtered or blocked." Another commenter, aqeel1506, explained that this message is used when traffic is blocked due to administrative policies like firewalls.

Exam Strategy

Memorize the specific sub-codes for ICMP Type 3 errors. Focus on distinguishing between technical failures (like Host Unreachable) and policy-based drops (Administratively Prohibited), as this distinction is critical for network forensics.

Frequently Asked Questions

What is the difference between Code 1 and Code 13?

Code 1 (Host Unreachable) is a routing failure, while Code 13 (Administratively Prohibited) is a deliberate drop by security policies.

Which ICMP code is for Port Unreachable?

Port Unreachable is ICMP Type 3, Code 3, indicating no service is listening on the destination port.

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Community Votes

B
100%

100% of anonymous learners picked answer B. Votes are pick records left by other test-takers — they are not the verified answer.

Discussion 4 contributions

Compiled from public community threads and reader submissions, lightly edited for clarity. Handles and vote tallies are shown as recorded, and comments reflect the views of individual contributors.

From public community threads 4

  1. aqeel1506 👍 1
    The correct answer is B. Administratively Blocked. ICMP Type 3, Code 13 is a specific error message that indicates that the packet was blocked due to administrative policies, such as firewall rules or access control lists (ACLs). This message is often used to indicate that the destination host or network is not allowed to receive traffic from the source host or network. Here's a brief overview of the other options: A. Host Unreachable (ICMP Type 3, Code 1) indicates that the destination host is not reachable, often due to a routing issue or a non-existent host. C. Port Unreachable (ICMP Type 3, Code 3) indicates that the destination port is not open or listening on the destination host. D. Protocol Unreachable (ICMP Type 3, Code 2) indicates that the destination host does not support the protocol used in the packet (e.g., TCP, UDP, etc.). ICMP error messages like these help network administrators diagnose and troubleshoot connectivity issues.
  2. 044f354 👍 1 Answered B
    Answer: B Explanation: ICMP Type 3/Code 13 indicates communication is administratively prohibited. (A) ❌ Host Unreachable is a different ICMP code. (B) ✅ Type 3/Code 13 means the packet was administratively filtered or blocked. (C) ❌ Port Unreachable is ICMP Type 3/Code 3, not Code 13. (D) ❌ Protocol Unreachable is a different ICMP code, not Type 3/Code 13. ----- If you agree, please UPVOTE. Each time you upvote someone with a yellow "SELECTED ANSWER: " banner (like me) your vote is added to the Community Vote Distribution, which helps the community by crowdsourcing correct answers.
  3. Elb 👍 1
    B> https://www.sharetechnote.com/html/IP_Network_ICMP.html#DestinationUnreacheable_Code13
  4. Dumas 👍 1
    B. Administratively Blocked

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