LFCS Networking Practice Question
A systems administrator is responsible for a production Linux server running CentOS 7 that provides SSH access to users. The administrator decides to tighten security by restricting SSH access to a specific management subnet 10.0.0.0/24. While connected to the server via SSH from a workstation on 10.0.0.50, the administrator adds the following iptables rule: iptables -A INPUT -p tcp --dport 22 -s 10.0.0.0/24 -j ACCEPT followed by iptables -P INPUT DROP. Immediately after the rule change, the administrator loses all connectivity to the server, including SSH. The administrator suspects that the new default policy dropped the existing SSH session. What is the most reliable method for the administrator to regain access to the server without rebooting?
⚠ Common exam trap
It's easy for candidates to assume iptables rules only affect new connections, forgetting that changing the default policy to DROP without a stateful rule for ESTABLISHED connections will immediately terminate existing sessions, and they overlook out-of-band management as the only non-reboot recovery option.
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
✓
Use IPMI or iDRAC to access the server's console and remove or modify the iptables rules.
IPMI (Intelligent Platform Management Interface) or iDRAC (Integrated Dell Remote Access Controller) provides out-of-band management access to the server's console, independent of the operating system's network stack. This allows the administrator to log in locally, remove or modify the iptables rules that dropped the SSH session, and restore connectivity without rebooting. Since the default INPUT policy was set to DROP, all new and existing SSH packets are blocked, but out-of-band management bypasses iptables entirely.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Use netcat to send a TCP reset packet to the SSH server.
Why it's wrong here
Not feasible without connectivity; netcat cannot restore a blocked session.
- ✗
Use iptables-save and iptables-restore from another host on the same subnet.
Why it's wrong here
Other hosts cannot connect to the server because the INPUT chain drops all traffic.
- ✓
Use IPMI or iDRAC to access the server's console and remove or modify the iptables rules.
Why this is correct
Out-of-band management provides console access independent of network.
- ✗
Boot the server into single-user mode and flush iptables rules.
Why it's wrong here
Requires physical access and disrupts production; networking may not be available.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This LFCS practice question is part of Courseiva's free Linux Foundation 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 LFCS exam.