This article describes how to Disable or Enable an IP forwarding in Linux.
Current IP forwarding status
Read a current state of IP forwarding:
# sysctl net.ipv4.ip_forward net.ipv4.ip_forward = 1
Currently, the output number 1 indicates that the IP forwarding is enabled. The above value is read from the Linux proc file system and more precisely from the actual file /proc/sys/net/ipv4/ip_forward file:
# cat /proc/sys/net/ipv4/ip_forward 1
Disable IP forwarding
To disable IP forwarding on a running Linux system run:
# sysctl -w net.ipv4.ip_forward=0 net.ipv4.ip_forward = 0
The above command actually writes number 0 into the above mentioned file /proc/sys/net/ipv4/ip_forward. If from some reason the above command fails you can attempt to disable the IP forwarding manually by:
echo 0 > /proc/sys/net/ipv4/ip_forward
The above change is not reboot persistent. To permanently disable the IP forwarding on your Linux system edit /etc/sysctl.conf and add the following line:
net.ipv4.ip_forward = 0