You might have noticed that your Ububtu server does not respond to ping requests after a reboot. In Ubuntu the networking is not started by default on boot. This might be causing the issue.

To start networking on boot, you may follow the below given instructions.

1. create a script in /etc/init.d with the following contents.

service networking start

2.set the file to executable mod

chmod +x <script>

3.update your runlevel configuration.

update-rc.d <script> defaults

Now try to ping it from a different ip to verify.