net.ipv4.ip_forward = 0 in /etc/sysctl.conf to the following:
net.ipv4.ip_forward = 1/sbin/sysctl net.ipv4.ip_forward
1, then IP forwarding is enabled. If it returns a 0, then you can turn it on manually using the following command:
/sbin/sysctl -w net.ipv4.ip_forward=1