Information
The net.ipv4.ip_forward and net.ipv6.conf.all.forwarding flags are used to tell the system whether it can forward packets or not.
Setting the flags 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 /etc/sysctl.conf or a /etc/sysctl.d/* file:
Example:
# printf "
net.ipv4.ip_forward = 0
" >> /etc/sysctl.d/60-netipv4_sysctl.conf
Run the following command to set the active kernel parameters:
# {
sysctl -w net.ipv4.ip_forward=0
sysctl -w net.ipv4.route.flush=1
}
IF IPv6 is enabled on the system:
Set the following parameter in /etc/sysctl.conf or a /etc/sysctl.d/* file:
Example:
# printf "
net.ipv6.conf.all.forwarding = 0
" >> /etc/sysctl.d/60-netipv6_sysctl.conf
Run the following command to set the active kernel parameters:
# {
sysctl -w net.ipv6.conf.all.forwarding=0
sysctl -w net.ipv6.route.flush=1
}