LPIC-1 Essential System Services and Networking Practice Question
Network Topology
Refer to the exhibit. The administrator is unable to SSH into the server (TCP port 22) from a remote host. The iptables rules are as shown. What is the most likely cause?
⚠ Common exam trap
Watch out — candidates often assume a default policy of ACCEPT overrides explicit DROP rules, but iptables processes rules sequentially and a matching DROP rule terminates processing, making the default policy irrelevant for packets that match it.
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 second rule drops all incoming traffic, including SSH.
The second rule in the iptables ruleset explicitly drops all incoming traffic with `iptables -A INPUT -j DROP`. Since SSH traffic on TCP port 22 is incoming from a remote host, it matches this rule before any later rule could accept it. The default policy being ACCEPT does not override explicit DROP rules; iptables processes rules sequentially, and the DROP rule terminates the packet's traversal, preventing SSH access.
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 default policy is ACCEPT, so SSH should be accepted.
Why it's wrong here
Explicit DROP overrides default policy.
- ✓
The second rule drops all incoming traffic, including SSH.
Why this is correct
The DROP rule matches all traffic not yet matched.
- ✗
The SSH service is not running.
Why it's wrong here
The issue is firewall, not service.
- ✗
The first rule only allows loopback, not SSH.
Why it's wrong here
Loopback rule allows lo interface only, not external SSH.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This LPIC-1 practice question is part of Courseiva's free LPI 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 LPIC-1 exam.