Last updated on March 22, 2012 by Dan Nanni
To check whether IP forwarding is enabled or not, you can run the following command. The output
1 means that IP forwarding is enabled, and
0 means that IP forwarding is disabled.
$ cat /proc/sys/net/ipv4/ip_forward
If you want to enable IP forwarding on the fly, you can use
sysctl command as follows. IP forwarding will be activated immediately without rebooting.
$ sudo sysctl -w net.ipv4.ip_forward=1
$ sudo sysctl -w net.ipv6.conf.all.forwarding=1
Note that IP forwarding enabled by
sysctl command does not remain active across reboots, which means that IP forwarding becomes disabled after rebooting.
If you want to enable IP forwarding permanently, edit
/etc/sysctl.conf as follows.
$ sudo vi /etc/sysctl.conf
net.ipv4.ip_forward=1 # For IPv4 net.ipv6.conf.all.forwarding=1 # For IPv6
Then reload sysctl.conf.
$ sudo sysctl -p /etc/sysctl.conf
Finally, restart networking to activate the change:
On CentOS, RHEL or Fedora:
$ sudo service network restart
On Debian or Ubuntu:
$ sudo /etc/init.d/networking restart
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