The SecOps Group Exam CNSP Topic 6 Question 11 Discussion

Actual exam question for The SecOps Group's CNSP exam

Question #: 11
Topic #: 6

[All CNSP Questions]

What is the response from a closed TCP port which is not behind a firewall?

AICMP message showing Port Unreachable

BA FIN and an ACK packet

CA RST and an ACK packet

DA SYN and an ACK packet

Show Suggested Answer

Suggested Answer: C

TCP uses a structured handshake, and its response to a connection attempt on a closed port follows a specific protocol when unobstructed by a firewall.

Why C is correct: A closed TCP port responds with a RST (Reset) and ACK (Acknowledgment) packet to terminate the connection attempt immediately. CNSP highlights this as a key scanning indicator.

Why other options are incorrect:

A: ICMP Port Unreachable is for UDP, not TCP.

B: FIN/ACK is for closing active connections, not rejecting new ones.

D: SYN/ACK indicates an open port during the TCP handshake.

by Marvel at Jul 08, 2025, 10:08 AM

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