3.1.1 Ensure IP forwarding is disabled (Scored)

Level 1 - Server
Level 1 - Workstation 

The net.ipv4.ip_forward flag is used to tell the system whether it can forward packets or not.

Setting the flag to 0 ensures that a system with multiple interfaces (for example, a hard proxy), will never be able to forward packets, and therefore, never serve as a router.

Run the following command and verify output matches:

# sysctl net.ipv4.ip_forward 
net.ipv4.ip_forward = 0

Set the following parameter in the /etc/sysctl.conf file:

net.ipv4.ip_forward = 0

Run the following commands to set the active kernel parameters:

# sysctl -w net.ipv4.ip_forward=0 
# sysctl -w net.ipv4.route.flush=1