When using DHCP on one of the Ethernet interfaces, a problem occurs: The mac address of the interfaces changes every time the GuruPlug starts up, which results in a different IP-address assigned by my router's DHCP. This is a little annoying because one of my interfaces is set for IP-forwarding in my ADSL-router (of course I could just set a static IP if I really don't want it to change, but I need DHCP because the interface gets the public IP).

I found the solution for the problem in this forum thread.

As soon as the GuruPlug starts up, enter the Marvell-prompt by pressing any key:

The command

printenv

will show you the environment variables. There should be two lines similar to

ethaddr=xx:xx:xx:xx:xx:xx
eth1addr=xx:xx:xx:xx:xx:xx

which show the current MAC-addresses (The "x" are of course hexadecimal numbers, depending on your variables). Now take a look at the back of your GuruPlug. There are three bar codes with numbers below, the two on the top are the MAC-addresses for the two network interfaces. The following picture shows the back of the GuruPlug to show you where to look for (of course I removed my MAC-addresses).

Now, set the environment variables with these two MAC-addresses with

setenv ethaddr <mac eth0>
setenv eth1addr <mac eth1>
saveenv

and restart the GuruPlug with

reset

This solution worked for me. You can check the assigned MAC-addresses after your GuruPlug has started up by using the command

# ifconfig

which shows a list of the network interfaces. The "HWaddr" entry shows your current MAC-address.