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XK0-006 Practice Question: A Linux administrator at a company that runs a…
You are a Linux administrator at a company that runs a web application in Docker containers on a single host. The application consists of a front-end container (nginx) and a back-end container (node.js). Recently, after a system update, the front-end container fails to start with the error: 'Error response from daemon: driver failed programming external connectivity on endpoint frontend: (iptables failed: iptables --wait -t filter -A DOCKER ! -i docker0 -o docker0 -p tcp -d 172.17.0.2 --dport 80 -j ACCEPT: iptables: No chain/target/match by that name)'. Which action should you take to resolve the issue?
⚠ Common exam trap
CompTIA often tests the misconception that iptables itself is broken or needs reinstallation, when the real issue is that Docker's custom iptables chains were lost and need to be recreated by restarting the Docker daemon.
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
✓
Restart the Docker daemon with systemctl restart docker
The error indicates that the Docker daemon's iptables rules are corrupted or missing, often caused by a system update that restarted or modified the iptables service. Restarting the Docker daemon with `systemctl restart docker` forces Docker to reinitialize its iptables chains (e.g., DOCKER, DOCKER-USER) and reapply the necessary rules, resolving the connectivity failure.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Restart the Docker daemon with systemctl restart docker
Why this is correct
Restarting Docker recreates its iptables chains and rules, fixing the missing chain error.
- ✗
Reinstall iptables
Why it's wrong here
Reinstalling iptables is unnecessary and may disrupt critical firewall rules; Docker normally manages its own rules.
- ✗
Change the network driver to macvlan
Why it's wrong here
Changing the driver is a workaround that avoids the issue but is not the recommended fix; it may also introduce other networking complications.
- ✗
Update the kernel to the latest version
Why it's wrong here
The issue is not kernel-related; a kernel update is unlikely to fix missing iptables chains and may introduce instability.
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Related to this question
Learn chapter
Linux Fundamentals and History
Key term
systemctl
systemctl is the command-line tool used to inspect, start, stop, enable, or disable services managed by the systemd init system in Linux.
Key term
User
A user is any person, system, or device that interacts with an IT service, resource, or identity system, typically authenticated through credentials and authorized to perform specific actions.
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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.