Ethernet turn off suddenlly in CentOS 6

This only work if your server is:
02:00.0 Ethernet controller: Intel Corporation 82574L Gigabit Network Connection
03:00.0 Ethernet controller: Intel Corporation 82574L Gigabit Network Connection and use the ethernet card e1000e



Import the public key:
rpm –import http://elrepo.org/RPM-GPG-KEY-elrepo.org
To install ELRepo for RHEL-5, SL-5 or CentOS-5:
rpm -Uvh http://elrepo.org/elrepo-release-5-3.el5.elrepo.noarch.rpm
To install ELRepo for RHEL-6, SL-6 or CentOS-6:
rpm -Uvh http://elrepo.org/elrepo-release-6-4.el6.elrepo.noarch.rpm

see this link:
click here