- A
nft add rule inet filter input ip saddr != 192.168.1.0/24 tcp dport 22 drop
This drops SSH from sources not within the management network.
- B
nft insert rule inet filter input tcp dport 22 drop
Why wrong: This would drop all SSH, including from management network.
- C
nft replace rule inet filter input handle 1 tcp dport 22 drop
Why wrong: This replaces a specific rule, but without knowing the handle, it's not appropriate.
- D
nft add rule inet filter input tcp dport 22 accept
Why wrong: This would accept all SSH, defeating the purpose.
Question 78 of 1,000
XK0-005 nftables rule syntax Practice Question
This XK0-005 practice question tests your understanding of security. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. A key principle to apply: nftables rule syntax. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
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'.
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.
Key principle: nftables rule syntax
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.
Related concept
nftables rule syntax
- ✗
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.
Common exam traps
Common exam trap: answer the scenario, not the keyword
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.
Detailed technical explanation
How to think about this question
Treat this as a scenario question. Identify the problem, the constraint, and the best action. Then compare each option against those facts.
KKey Concepts to Remember
- nftables rule syntax
- IP address negation
- Rule ordering
- TCP destination port matching
TExam Day Tips
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
nftables rule syntax
Real-world example
How this comes up in practice
A network engineer segments a warehouse floor into three subnets: 20 scanners, 5 printers, and 2 management hosts. Picking the wrong mask wastes addresses or leaves too few usable hosts. Exam questions test whether you can apply CIDR notation, calculate block size, and identify the correct usable-host range for a given prefix.
Visual reference
What to study next
Got this wrong? Here's your next step.
Review nftables rule syntax, then practise related XK0-005 questions on the same topic to reinforce the concept.
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FAQ
Questions learners often ask
What does this XK0-005 question test?
Security — This question tests Security — nftables rule syntax.
What is the correct answer to this question?
The correct answer is: 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.
What should I do if I get this XK0-005 question wrong?
Review nftables rule syntax, then practise related XK0-005 questions on the same topic to reinforce the concept.
What is the key concept behind this question?
nftables rule syntax
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Last reviewed: Jul 4, 2026
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