@blebbens It's been a while. But if I remeber it correctly you have to set #define SOFTSPI in MyConfig.h too. Don't forget to comment it back when you're compiling a sketch for a node. My router uses DHCP as well. But I can assign a static IP in the sketch. Shouldn't be a problem. I'm not sure, but I think the arduino can't handle DHCP, it's a really simple ethernet card. So you need to assign an IP in the sketch.

I modified MyConfig.h file and RFM69 driver to allow you build gateway (ethernet or MQTT) with W5100 ethernet and RFM69 radio modules using SoftSPI bus. You can find it at: https://github.com/gieemek/RFM69_softSPI-for-MySensors-2.1.1