RealTek Ethernet: RTL8169S/SB/SC RTL8168B RTL8101E RTL8110
Hardware con el problema >>- RTL8169S/SB/SC (Gigabit Ethernet with PCI interface).
- RTL8168B (Gigabit Ethernet with PCI-Express interface).
- RTL8101E (Fast Ethernet with PCI-Express interface).
- RTL8110
Esta es la pagina en la que informan que en CentOS 5:
* Drivers not included in the kernel as of 2.6.20.4.
http://wiki.centos.org/HardwareList/CentOS5/RealTek/r1000
Yo lo solucione ayudado de :
http://www.vincentverhagen.nl/2007/12/03/
realtek-linux-driver-automatic-compile-for-kernel/
En este articulo te dan el script y el driver para el CentOS >>
December 3, 2007
Realtek Linux driver automatic compile for kernel
Sometimes you’ll have to update your Linux kernel. Not very often, but sometimes anyway
If, like me, you use a mainboard with a builtin Realtek ethernet controller, chances are that after installing your new kernel, the ethernet controller doesn’t come up. The problem is that your Linux kernel doesn’t have the correct module/driver.
You can very easily compile and install the driver by hand, but I tend to forget that and start wondering why things aren’t working 
I’ve written a small script that checks to see if the correct kernel module exists. If not, it compiles the module and restarts the network services.
It’s compatible with CentOS 4(.5) and 5, but will most likely work with all Red Hat derivates.
Download the drivers and extract them in /usr/src like this:
cd /usr/src
tar xzf where-you-put-the-tgz-file/realtek_r1000.tgz
Copy the script to a location that makes sense to you (the script assumes /usr/src/LAN):
cp where-you-put-the-script/r1000.sh /usr/src/LAN
Edit your /etc/rc.d/rc.local to execute the r1000.sh file on system boot.
That should do the trick!
The drivers I’ve included with this post will work for RTL8169S/SB/SC, RTL8168B and RTL8101E chipsets.
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