Details
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.
Solution
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
Supportive Information
The following resource is also helpful.
This security hardening control applies to the following category of controls within NIST 800-53: System and Communications Protection.This control applies to the following type of system Unix.