CND Network Perimeter Protection Practice Question
An attacker performs a TCP SYN flood attack against a perimeter web server protected by a firewall. The security engineer enables SYN cookies on the firewall/router. How does this feature mitigate the attack?
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The firewall encodes connection parameters into the sequence number (SYN cookie) without allocating memory state until the client responds with an ACK.
SYN cookies allow the firewall/router to respond to SYN requests without allocating state table memory until the three-way handshake is fully completed by the client ACK.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
The firewall drops all incoming SYN packets immediately.
Why it's wrong here
Dropping all SYN packets would block legitimate users from connecting.
- ✓
The firewall encodes connection parameters into the sequence number (SYN cookie) without allocating memory state until the client responds with an ACK.
Why this is correct
This prevents connection table exhaustion during a SYN flood.
- ✗
The firewall resets the TCP window size to zero for all external connections.
Why it's wrong here
Zero window size halts communication rather than mitigating SYN floods.
- ✗
The firewall proxies the TCP handshake by establishing a full connection before forwarding traffic to the server.
Why it's wrong here
This describes a SYN proxy, not SYN cookies.
Visual reference
About these practice questions
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JA
Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed August 2026 · checked against the official EC-Council exam blueprint
This CND practice question is part of Courseiva's free EC-Council certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the CND exam.