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can not be build on Centos6.x.
The driver has not yet reached the main stream and package released in
http://www.linuxfoundation.org/collaborate/workgroups/networking/alx does not compile for Centos.
To solve this tedious problem you need to get the original Atheros driver (from Atheros), but after they were bought by Qualcomm this can not be tracked any more.
Download this file
Then unrar it and build it - just run make, then perform "sudo insmod alx.ko", and the eth0 appears, then just "sudo ifconfig eth0 up" and you are ready to go.