Some software likes the MAC address of your first ethernet device to be set to a specific value. On Linux, this is trivial:
Edit /etc/udev/rules.d/70-persistent-net.rules to name your ethernet card eth1. To make these changes take effect, use modprobe to remove and re-insert the kernel module for your card's driver. If you don't know what this means, reboot your system.
# modprobe dummy # ip link set name eth3 dev dummy0 # ifconfig eth0 hw ether DEADBEEFCAFE
To make this permanent, add the following lines to the listed files:
iface eth0 inet static hwaddress DE:AD:BE:EF:CA:FE
SUBSYSTEM=="net", KERNEL=="dummy0", NAME="eth0"