I have two servers, 198.162.0.4 and 198.162.0.10, that were connected across a LAN. They are the components of a DMZ where 198.162.0.4 is the wen server and 198.162.0.10 the application server. 198.162.0.4 is running Ubuntu 11.04 while 198.162.0.10 is running Ubuntu 11.10. I had to restart 198.162.0.10 because Unity froze up. (I have since replaced it with Gnome.) Ever since I started it up again, I cannot get connectivity with 198.162.0.4. When I try

ping 192.162.0.4

PING 192.162.0.4 (192.162.0.4) 56(84) bytes of data.

ping 192.162.0.10

sudo iptables -A OUTPUT -s 192.162.0.4 -j ACCEPT
sudo iptables -A OUTPUT -d 192.162.0.4 -j ACCEPT
sudo iptables -A INPUT -s 192.162.0.4 -j ACCEPT
sudo iptables -A INPUT -d 192.162.0.4 -j ACCEPT

Unity under 11.04 onward had a lot of bugs and user complaints.

As root have you run dhclient since the reboot?

Did you make changes with ethtool before the reboot? (this would be my first place to check because ethtool changes are kernel persistent only)

This is embarrassing but my problem was a typo in the iptables. I was typing 192.162.0.4 where it should have been 192.168.1.4.

Sorry about that,
Peter.

That is okay, getting an answer back as to why is great.