What effect does the command iptables -A INPUT -d 10.142.232.1 -p tcp --dport 20:21 -j ACCEPT have on TCP packets?

What effect does the command iptables -A INPUT -d 10.142.232.1 -p tcp --dport 20:21 -j ACCEPT have on TCP packets?

• A. Accept TCP traffic from any source
• B. Drop all TCP traffic from 10.142.232.1
• C. Accept all TCP traffic on ports 20 and 21
• D. Block TCP traffic on port 21 only

Answer: (C)

The command `iptables -A INPUT -d 10.142.232.1 -p tcp --dport 20:21 -j ACCEPT` specifically allows TCP packets that are destined for the IP address 10.142.232.1 and that are using ports 20 and 21. This command is structured to append a rule to the iptables INPUT chain. It specifies that any incoming TCP traffic directed at the specified destination IP (10.142.232.1) on the defined ports (20 and 21) should be accepted. Consequently, this rule explicitly permits traffic for both ports simultaneously, enabling communication for protocols that typically run on these ports, such as FTP (File Transfer Protocol), which operates on port 21 for control and port 20 for data transfer. It's important to note that the other choices do not accurately describe the behavior of the command. The command does not accept TCP traffic from any source, only traffic directed to a specific destination IP. It also does not drop traffic or block any ports, which further confirms that the correct interpretation is related to the acceptance of TCP traffic on the specified ports.

The command iptables -A INPUT -d 10.142.232.1 -p tcp --dport 20:21 -j ACCEPT specifically allows TCP packets that are destined for the IP address 10.142.232.1 and that are using ports 20 and 21.

This command is structured to append a rule to the iptables INPUT chain. It specifies that any incoming TCP traffic directed at the specified destination IP (10.142.232.1) on the defined ports (20 and 21) should be accepted. Consequently, this rule explicitly permits traffic for both ports simultaneously, enabling communication for protocols that typically run on these ports, such as FTP (File Transfer Protocol), which operates on port 21 for control and port 20 for data transfer.

It's important to note that the other choices do not accurately describe the behavior of the command. The command does not accept TCP traffic from any source, only traffic directed to a specific destination IP. It also does not drop traffic or block any ports, which further confirms that the correct interpretation is related to the acceptance of TCP traffic on the specified ports.