XK0-006 Security Practice Question
A system administrator needs to add an iptables rule to drop incoming TCP traffic on port 22 (SSH) from the IP address 10.0.0.100. Which command should be used?
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
✓
iptables -A INPUT -p tcp --dport 22 -s 10.0.0.100 -j DROP
The correct syntax is iptables -A INPUT -p tcp --dport 22 -s 10.0.0.100 -j DROP. The chain is INPUT, protocol tcp, destination port 22, source IP, and target DROP.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
iptables -A INPUT -p udp --dport 22 -s 10.0.0.100 -j DROP
Why it's wrong here
SSH uses TCP, not UDP.
- ✗
iptables -I OUTPUT -p tcp --sport 22 -d 10.0.0.100 -j DROP
Why it's wrong here
This affects outgoing traffic, not incoming SSH.
- ✗
iptables -A FORWARD -p tcp --dport 22 -s 10.0.0.100 -j DROP
Why it's wrong here
The FORWARD chain is for routed traffic, not input to the local system.
- ✓
iptables -A INPUT -p tcp --dport 22 -s 10.0.0.100 -j DROP
Why this is correct
This appends a rule to the INPUT chain to drop SSH from that source.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This XK0-006 practice question is part of Courseiva's free CompTIA 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 XK0-006 exam.