SK0-005 security-disaster-recovery Practice Question
Network Topology
Refer to the exhibit. A Linux server's local firewall is configured as shown. The administrator is unable to perform backups to a network-attached storage (NAS) device using TCP port 10000. Which firewall rule is causing the issue?
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 DROP all rule at the end blocks all traffic except SSH.
Option D is correct. The INPUT chain contains an explicit DROP all rule at the end, which blocks any traffic not explicitly allowed. The only allowed traffic is SSH on port 22. The backup traffic on port 10000 matches the DROP rule and is therefore dropped. Option A is incorrect because the policy ACCEPT is overridden by the explicit DROP. Option B allows SSH traffic but does not affect port 10000. Option C about subnets is irrelevant to the local firewall shown.
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 INPUT policy is set to ACCEPT.
Why it's wrong here
Although the default policy is ACCEPT, the explicit DROP rule at the end of the chain overrides it for all packets not matching earlier rules.
- ✓
The DROP all rule at the end blocks all traffic except SSH.
Why this is correct
The DROP rule matches all packets that were not explicitly accepted (only port 22), including the backup traffic on port 10000.
- ✗
The NAS device uses a different subnet.
Why it's wrong here
Subnet addressing is a network configuration issue, not a local firewall rule; the firewall is dropping packets regardless of source/destination subnet.
- ✗
The SSH ACCEPT rule is allowing traffic.
Why it's wrong here
The SSH rule correctly permits port 22 traffic but does not interfere with port 10000 traffic.
Visual reference
Go deeper
Related to this question
Learn chapter
Storage Management (RAID, SAN, NAS)
Key term
Firewall
A firewall is a network security system that monitors and controls incoming and outgoing traffic based on predetermined security rules to protect trusted internal networks from untrusted external networks.
Key term
NAS
NAS is a dedicated file-level storage device connected to a network, providing centralized data access to multiple clients via standard protocols like NFS or SMB.
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Same concept, more angles
2 more ways this is tested on SK0-005
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. Refer to the exhibit. A web server is running on port 80, but users are unable to connect. The administrator has confirmed the web server service is running. The output of iptables -L is shown. What is the most likely reason for the connectivity issue?
medium- A.The server's default gateway is incorrect
- ✓ B.The firewall is blocking incoming traffic on port 80
- C.SELinux is enforcing and blocking port 80
- D.The web server is not bound to the correct IP address
Why B: The iptables rules accept only related/established traffic and drop SSH. The catch-all REJECT rule blocks all other incoming connections, including HTTP on port 80, because no explicit ACCEPT rule exists for it.
Variation 2. Refer to the exhibit. A server administrator configured iptables rules on a Linux server. Immediately afterward, they are unable to connect to the server via SSH. The output of 'iptables -L INPUT -n' is shown. What is the most likely cause of the connectivity issue?
medium- A.The last DROP rule blocks all traffic, including established SSH sessions.
- ✓ B.The DROP rule for port 22 appears before the ACCEPT rule, causing all SSH packets to be dropped.
- C.The default INPUT policy is set to ACCEPT, allowing all traffic.
- D.The ACCEPT rule for port 22 is missing the ESTABLISHED state, preventing return traffic.
Why B: iptables processes rules in order. The DROP rule for destination port 22 appears before the ACCEPT rule, so all incoming SSH packets are dropped before the ACCEPT rule can permit new connections.
JA
Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed July 2026 · checked against the official CompTIA exam blueprint
This SK0-005 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 SK0-005 exam.