I ran into the problem that I couldn’t get my DomU’s on a Hetzner EQ4 to connect to the internet.
Unfortunately this is because of the strange network settings Hetzner is using. There is a German manual how to set up a XEN server in their environment, but it is missing one really important part. Hetzner limits the access on their network equipment to the MAC address of your server. Hetzner is not giving you the possibility to set / create new MAC addresses for subnets.
Assuming you are using Debian Squeeze and your server is already set up, you will have to set a point to point connection in the Dom0 and each DomU.
DomO has the regular ip 178.x.x.x and one from the subnet 88.x.x.x – gateway is 178.x.x.1.
Edit the /etc/network/interfaces and add pointtopoint 178.x.x.1 after gateway. This should be the same ip address as your gateway.
For the routing you need one ip address of your subnet on the Dom0 installed. This will also be your default gateway for all DomU’s.
Add the default gateway as a pointopoint connection on every DomU and it should work.
Don’t forget to restart network or reboot the machine and instances.