CND Network Attacks And Defense Strategies Practice Question

A security engineer is configuring a Snort Intrusion Prevention System (IPS) rule to detect ICMP echo requests with payloads larger than 1000 bytes, which may indicate covert channel data exfiltration. Which rule header and options combination is correct?

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

✓

alert icmp any any -> any any (msg:"Large ICMP Payload Detected"; dsize:>1000; sid:1000001; rev:1;)

A correct Snort rule structure requires the action (alert/drop), protocol (icmp), source/destination IPs and ports, and options such as dsize:1000 to check packet payload size.

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

✗
log ip any any -> any any (msg:"ICMP Check"; length:1000; sid:1000001; rev:1;)
Why it's wrong here
The 'length' option is invalid in Snort syntax; 'dsize' is the correct keyword for payload sizing.
✓
alert icmp any any -> any any (msg:"Large ICMP Payload Detected"; dsize:>1000; sid:1000001; rev:1;)
Why this is correct
This rule correctly specifies ICMP protocol and uses the dsize option to flag payloads over 1000 bytes.
✗
drop tcp any any -> any 80 (msg:"ICMP Large Payload"; payload_size:>1000; sid:1000001; rev:1;)
Why it's wrong here
This rule targets TCP port 80 rather than the ICMP protocol.
✗
pass udp any any -> any 53 (msg:"ICMP Alert"; size:1000; sid:1000001; rev:1;)
Why it's wrong here
This rule specifies UDP port 53 (DNS) instead of ICMP.

About these practice questions

One of 323 original CND practice questions on Courseiva, each with a full explanation and wrong-answer analysis — not exam dumps or protected exam content. Learn why practice questions differ from exam dumps →

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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

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