====== Ubuntu - Networking - Configuration - IP Forwarding ======

**IP forwarding** is the ability for an operating system to accept incoming network packets on one interface, recognize that it is not meant for the system itself, but that it should be passed on to another network, and then forwards it accordingly.

----

===== Enable Port Forwarding Permanantly =====

Uncomment or add this line to  **/etc/sysctl.conf**:

<file bash /etc/sysctl.conf>
net.ipv4.ip_forward=1
</file>

To enable the changes made in sysctl.conf, run:

<code bash>
sysctl -p
</code>

----

===== Enable IP Forwarding on the fly =====

To enable IP Forwarding, without rebooting the system:

<code bash>
sysctl -w net.ipv4.ip_forward=1
</code>

or

<code bash>
echo 1 > /proc/sys/net/ipv4/ip_forward
</code>

<WRAP info>
**NOTE:**  The setting is changed instantly.

  * However the result will not be preserved after rebooting the system.

</WRAP>

----


===== Check if Port Forwarding is Enabled =====

<code bash>
cat /proc/sys/net/ipv4/ip_forward
</code>

returns:

<code bash>
1
</code>

<WRAP info>
**NOTE:**

  * **0**:  Port forwarding is not enabled.
  *  **1**:  Port forwarding is enabled.
</WRAP>