Problem scenario
You want to enable IP version 4 forwarding on an Ubuntu server permanently. How do you do this without rebooting?
Solution
1. Run this command:sudo sysctl -w net.ipv4.ip_forward=1
2. Modify the /etc/sysctl.conf file. Use "sudo vi /etc/sysctl.conf"
Uncomment out this stanza:
net.ipv4.ip_forward=1
3. Save the changes. You are done.