LFCS Question #225: Real Exam Question with Answer & Explanation

Question

What does the following iptables rule accomplish: iptables A INPUT s 208.77.188.166 d 10.142.232.1 p tcp dport 22 j ACCEPT

Options

• AAccepts traffic on port 22 only from the hosts 208.77.188.166 and 10.142.232.1.
• BForwards all requests from the host 10.142.232.1 on port 22 the internal host 208.77.188.166
• CForwards all requests from the host 208.77.188.166 on port 22 the internal host 10.142.232.1
• DDrops traffic on port 22 only from the hosts 208.77.188.166 and 10.142.232.1.

Explanation

This iptables rule permits TCP traffic on destination port 22, originating from 208.77.188.166 and destined for 10.142.232.1, to be accepted.

Common mistakes.

• A. The rule specifies a single source IP (-s) and a single destination IP (-d), not traffic from two sources or to two destinations.
• B. This rule is in the INPUT chain, which processes traffic destined for the local machine, not for forwarding to another internal host. Also, the source and destination IPs are reversed from the interpretation given.
• D. The j ACCEPT target explicitly allows traffic, it does not drop it.

Concept tested. Iptables rule interpretation (source, destination, port)

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

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