I recently had a bare metal SuperMicro server which was running an installation of CentOS 6.6.
There was an issue with it where the NIC would randomly stop working.
There seems to be an issue with PCIe Active State Power Management in some Linux Kernels (see http://bugs.centos.org/view.php?id=6814 as example).
The workaround for this is pretty easy.. Just disable the PCIe ASPM at the kernel level.
To see the state of PCIe ASPM, toss this at the term:
Server124# dmesg|grep PCIe
This will relate your current state.
To disable this, edit Grub:
and then pop this line at the end of your boot line:
give it a reboot and run the
command again and do some testing.