On some newer model Intel NICs they fall asleep at random when using Centos 6.X, or even other OS’s. To combat this, there is a simple addition to the grub.conf that will disable PCIe_ASPM. At the command line enter:
vi /etc/grub.conf
Once in the grub.conf file, insert this into the end of the kernel line:
pcie_aspm=off
It should then look like this: 
Exit, save, and reboot for changes to take effect. To check that changes were indeed made, use the following:
dmesg|grep PCIe
It should return a PCIe Disabled message, confirming the changes were made successfully: 
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