All CentOS versions released after June 2010 include proper drivers for this chipset so all the below information is obsolete. If run a recent CentOS version and you encounter issues with an Attansic wired network card, please consider installing the package kmod-atl1 distributed by the ElRepo 3rd party repository. See https://wiki.centos.org/AdditionalResources/Repositories for details.
The Attansic L1 is included as the onboard network device for many mainboards
No version of Centos <= 5.6 includes a driver for this chipset.
The driver for this chipset has been merged in the mainline kernel in Feb 2007, as of kernel version 2.6.20-git5. Centos <=5.6 uses older kernels for which no backport exists yet.
Output of `lspci -v`
02:00.0 Ethernet controller: Attansic Technology Corp. L1 Gigabit Ethernet Adapter (rev b0)
- Subsystem: ASUSTeK Computer Inc. Unknown device 8226
- Flags: bus master, fast devsel, latency 0, IRQ 2301
- Memory at dffc0000 (64-bit, non-prefetchable) [size=256K]
- Expansion ROM at dffa0000 [disabled] [size=128K]
- Capabilities:  Power Management version 2
- Capabilities:  Message Signalled Interrupts: Mask- 64bit+ Queue=0/0 Enable+
- Capabilities:  Express Endpoint IRQ 0
- Capabilities: [6c] Vital Product Data
There is a driver available from http://atl1.sourceforge.net/. Quoting that site:
IMPORTANT NOTE: This is a vendor version of the L1 driver. It was written by Attansic. We do not support this driver. It's offered here merely as a courtesy to make your life easier. If you have a problem with the driver, contact Attansic/Atheros directly.
IMPORTANT NOTE: The Attansic vendor version of drivers prior to 126.96.36.199 have a problem: TSO is broken, and that results in horrible transmit performance. It's fixed in 188.8.131.52. Don't use a vendor version older than 184.108.40.206!
According to your needs, you can select one of the following solutions:
Update to a more recent CentOS release
Since CentOS 5.7, the driver for this chipset is included in the kernel.
Prebuilt kernel module
The driver may also be downloaded as a kABI tracking kmod RPM package from the ELRepo repository. Select the kmod package that matches your kernel and install it according to the instructions provided by that repository.