A network interface based on Realtek RTL8111/8411 revision 06 seems to be up but with no connectivity. The issue is that some newer Realtek chipsets don't get compiled with the right drivers. This causes the interface to be up without any network traffic. In order to fix this issue, the older driver needs to be downloaded from the Realtek site and compiled manually. The driver can be downloaded from http://www.realtek.com.tw/Downloads/.

Since this driver is manually installed, during a kernel update it will get updated automatically. To prevent this and ensure the driver builds itself automatically when a new kernel is installed, run the following commands and then reboot the node:

# apt-get install dkms build-essentials pve-headers-2.6.32-25-pve
# cat <<EOF > /usr/src/r8168-8.037.00/dkms.conf
PACKAGE_NAME=r8168...