Right after installation the compute nodes have no access to the outside network/world. This is of course problematic (especially if you have a licence server on the network). There are two ways how to fix this. First, either route traffic to the outside network via the frontend. Good luck with that, I have tried everything twice with no success and asked the experts here and here. You have to love “I'd simply start over on your frontend”.

The second way is to be lucky and have a second interface on each compute node which you can connect to the outside world (or switch). Even so, this is not straightforward. Note that the second interface of a rocks compute node is not installed by default.