Linux : Disable and enable IPv4 forwarding

A quick note on how to disable or enable IP (version 4) forwarding in Linux. IP forwarding is a routing process used to determine which path a packet or datagram can be sent. If you are using Linux as a web server and you do not want your web server to be used in this routing process. You can disable the IP forwarding.

There are couple of ways you can disable IP forwarding.

In /etc/sysctl.conf file, change net.ipv4.ip_forward = 0

or issue this command :

>sudo sysctl -w net.ipv4.ip_forward=0

to check if the IP forwarding has been disabled, you can view the /proc/sys/net/ipv4/ip_forward file content. If it is 0 that means IP forwarding has been disabled.

In case you want to reverse your action, you can enable IP forwarding back with this command.

>sudo sysctl -w net.ipv4.ip_forward=1

Reference :

https://en.wikipedia.org/wiki/IP_forwarding