LFCS Question #224: Real Exam Question with Answer & Explanation

Question

What does the following iptables rule accomplish: iptables A INPUT s 208.77.188.166 j DROP

Options

• AForwards all incoming traffic to the host 208.77.188.166.
• BAccepts all traffic from 208.77.188.166.
• CNothing, there is a syntax error.
• DDrops all traffic from 208.77.188.166.

Explanation

The iptables rule described will block all incoming network traffic originating from the specified source IP address.

Common mistakes.

• A. This rule does not forward traffic; it explicitly blocks it. Forwarding is typically handled by the FORWARD chain or NAT rules.
• B. The j DROP target explicitly discards traffic, it does not accept it. The ACCEPT target is used for allowing traffic.
• C. The rule iptables -A INPUT -s 208.77.188.166 -j DROP has correct iptables syntax and will execute as intended.

Concept tested. Iptables basic packet filtering

Reference. https://linux.die.net/man/8/iptables

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