XK0-006 nftables rule syntax Practice Question
A server running nftables has a rule set that allows incoming SSH from the management network (192.168.1.0/24). An administrator needs to insert a rule to drop SSH from all other sources. Which nft command accomplishes this? Assume the input chain is 'input' and the table is 'inet filter'.
⚠ Common exam trap
Candidates often confuse 'add' vs 'insert' in nftables. The question says 'insert a rule', but the correct approach is to append a drop rule after the allow rule. Adding the drop rule before the allow rule would make the allow rule irrelevant. 'Add rule' appends, which is correct here.
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
✓
nft add rule inet filter input ip saddr != 192.168.1.0/24 tcp dport 22 drop
The correct command is A. The existing rule allows SSH from 192.168.1.0/24. To drop SSH from all other sources, we need a rule that matches packets with source IP address not in that subnet and destination port 22, and then drops them. The `add rule` subcommand appends the rule to the chain, which is appropriate because the allow rule for the management network should remain first. Using `ip saddr != 192.168.1.0/24` properly negates the source subnet. Option B drops SSH from any source (including the management network), which would block the allowed traffic. Option C replaces an existing rule by handle but does not specify the source condition. Option D accepts SSH from all sources, which is not desired. Therefore, A is correct.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
nft add rule inet filter input ip saddr != 192.168.1.0/24 tcp dport 22 drop
Why this is correct
This drops SSH from sources not within the management network.
- ✗
nft insert rule inet filter input tcp dport 22 drop
Why it's wrong here
This would drop all SSH, including from management network.
- ✗
nft replace rule inet filter input handle 1 tcp dport 22 drop
Why it's wrong here
This replaces a specific rule, but without knowing the handle, it's not appropriate.
- ✗
nft add rule inet filter input tcp dport 22 accept
Why it's wrong here
This would accept all SSH, defeating the purpose.
Visual reference
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Related to this question
Learn chapter
Installing Linux and Package Management
Key term
SSH
SSH (Secure Shell) is a cryptographic network protocol that provides secure, encrypted communication and remote administration between two devices over an unsecured network.
Key term
Subnet
A subnet is a logical subdivision of an IP network, created by partitioning a larger network address space using subnet masks.
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JA
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.