Linux Shell Scripting Cookbook - Third Edition

How it works...

iptables is the command used to configure the firewall on Linux. The first argument in iptables is -A, which instructs iptables to append a new rule to the chain, or -I, which places the new rule at the start of the ruleset. The next parameter defines the chain. A chain is a collection of rules, and in earlier recipes we used the OUTPUT chain, which is evaluated for outgoing traffic, whereas the last recipes used the INPUT chain, which is evaluated for incoming traffic.

The -d parameter specifies the destination to match with the packet being sent, and  -s specifies the source of a packet. Finally, the -j parameter instructs iptables to jump to a particular action. In these examples, we used the DROP action to drop the packet. ...