Basic firewall using iptables

A firewall is a network service which is used to filter network traffic for unwanted traffic, block it, and allow the desired traffic to pass. The most powerful tool on Linux is iptables, which has kernel integration in recent versions of the kernels.

How to do it...

iptables is present, by default, on all modern Linux distributions. We will see how to configure iptables for common scenarios.

  1. Block traffic to a specific IP address:
    #iptables -A OUTPUT -d 8.8.8.8 -j DROP

    If you run PING 8.8.8.8 in another terminal before running the iptables command, you will see this:

    PING 8.8.8.8 (8.8.8.8) 56(84) bytes of data.
64 bytes from 8.8.8.8: icmp_req=1 ttl=56 time=221 ms
64 bytes from 8.8.8.8: icmp_req=2 ttl=56 time=221 ms ...

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