Linux: Iptables Find / Check Banned IP Address

On a Linux system, you can use the iptables utility to find banned IP addresses that are blocked by the firewall. Iptables is a command-line tool that allows you to configure the firewall rules on your system.

To find banned IP addresses in iptables, you can use the -L option to list the current firewall rules, and the -n option to display the rules in numeric format (i.e., without resolving hostnames). You can also use the -v option to display the rules in verbose mode, which will show more information about each rule.

For example, to list the rules in the INPUT chain (which handles incoming packets) in numeric format, you can run the following command:

iptables -nvL INPUT

This will show a list of rules, with each rule showing the packet and byte counts, the target, the protocol, and the source and destination addresses. If a rule has a target of DROP or REJECT, it indicates that packets matching that rule will be dropped or rejected, respectively.

You can also use the grep command to search for specific IP addresses in the output of the iptables command. For example, to search for the IP address 1.2.3.4 in the INPUT chain, you can run:

iptables -nvL INPUT | grep 1.2.3.4

This will show the rule (if any) that matches the IP address 1.2.3.4.

Keep in mind that iptables rules are organized into chains, and there are several built-in chains that handle different types of packets. In addition to the INPUT chain, you may also want to check the OUTPUT and FORWARD chains for banned IP addresses.

If you are not familiar with iptables or firewall configuration on Linux, you may want to consult the iptables documentation or a reference guide for more information.