LPI Certification / CompTIA Linux+ Practice Test

Answer - A - You should use the iptables -t filter -A INPUT -s 0/0 -p tcp -dport 23 -j DROP command to configure your Linux firewall to block all network traffic addressed to the Telnet service on the local system.

Key Takeaway: All IP packets inspected by iptables pass through a sequence of built-in tables for processing. Each of these queues inspects a particular type of packet activity and is controlled by an associated packet filtering chain. The second table is the filter queue. This has three built-in chains on which you can place your firewall policy rules; forward chain, input chain, and output chain.