Checking for an iptables allow rule | LinuC Level 1 102 Exam original practice question

1.10.2Basic

Check whether INPUT contains a rule accepting TCP port 22 without adding or deleting rules.

Which command is appropriate?

Hint 1: Focus on security boundaries

Separate protected account data, service availability directives, and packet-filtering policy before comparing the choices.

Hint 2: Key terms

Review the short definitions of protected account data, service controls, and firewall layers involved.

Rule check: A query that tests whether a specified rule exists without changing the chain.
Match condition: A protocol, port, address, or other predicate used to match traffic.
ACCEPT: A packet action that permits matching traffic to continue.
Append operation: An operation that adds a new rule to the end of a chain.
Delete operation: An operation that removes a matching rule from a chain.
Non-mutating query: A check that inspects firewall state without adding or removing rules.

Detailed explanation

Incorrectiptables -A INPUT -p tcp --dport 22 -j ACCEPT

Incorrect. -A appends the allow rule.

Incorrectiptables -D INPUT -p tcp --dport 22 -j ACCEPT

Incorrect. -D deletes a matching rule.

Incorrectiptables -L INPUT --dport 22

Incorrect. -L does not take --dport as a direct filter in this form.

Correctiptables -C INPUT -p tcp --dport 22 -j ACCEPT

Correct. -C checks for the exact rule.

An example you can run in a temporary verification environment.

iptables --help 2>&1 | grep -E -- '^-C|check' | head -n 2

check ruleまたは-Cに関するhelp行

Foundation review

Sensitive authentication data stored separately from ordinary account records.

Whether a service can start automatically or be activated on demand.

A host firewall rule set that permits or rejects network packets.

Question IDKL-102-1148

Environmentiptables help / rule変更なし

Last technical review2026-08-20

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