Today I reboot my CentOS 6 server, and I realized that the network connection was lost after the upgrade. To be exact, it seems that the problem was caused by the new kernel: 2.6.32-573.1.1.el6.x86_64. It modified the network settings of the server with manual settings (server with DHCP is not affected). Here is how I fix the problem (You will need physical access to the server):

I have noticed that the adapter profile has been modified to something that doesn’t make scenes. If you compare the network settings, you will notice the following differences:

#Before the upgrade
#cat /etc/sysconfig/network-scripts/ifcfg-em1  
PREFIX=24

#After the upgrade
#cat /etc/sysconfig/network-scripts/ifcfg-em1  
PREFIX=32

So I simply make the modifications to the adapter settings and restart the network service, i.e.,

sudo service network restart

And the network connection is back!

That’s it! Hope this tutorial saves you from heart attack.

–Derrick