Check the current setting:
sysctl net.ipv4.ip_forward
net.ipv4.ip_forward=0 #disable
net.ipv4.ip_forward=1 #enable
Enable IP forwarding:
sudo sysctl net.ipv4.ip_forward=1
Disable IP forwarding:
sudo sysctl net.ipv4.ip_forward=0
To make change perminant acroos reboot:
sudo vi /etc/sysctl.conf
Find the following text:
#Uncomment the next line to enable packet forwarding for IPv4
#net.ipv4.ip_forward=1
Save and exit.
Make the changes take effect immediately:
sudo sysctl -p