Question 142 of 144
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
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Last reviewed: Jul 26, 2026
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