@mfalkvidd yes I've read that, even multiple times. I've check the wiring 10 times as well and cannot find a difference. Also changed to another W5100 board as well as a different Arduino Uno board to make sure it is not a board issue. The problem stays the same. What I've noticed as a difference is that my W5100 runs on 5V and not on 3.3V as indicated in the wiring table. Connecting the W5100 with 3.3V doesn't start (boot up) the board.

I've spent hours and hours to get the W5100 Ethernet Module working on my Arduino Nano board and unfortunately without success. I'm using the MySensors version 2.0 with the Arduino AVR Boards 1.6.15 installed. I don't understand the issue at all. I cannot ping W5100 should, not if I use a static IP or if I configure to use DHCP. I've tested it with and without the NRF24L01 Radio connected and no luck. I've checked the wires already 10 times. This is the wire-ring info:
W5100 <=> Arduino Nano
VDD <=> Pin 27 / +5V
NSS <=> Pin 13 / D10
MOSI <=> Pin 14 / D11
GND <=> Pin 4
SCK <=> Pin 16 / D13
MISO <=> Pin 15 / D12

Is this the correct wire configuration? What else can I do to debug this?

On the W5100 I see the link led blinking on a regular basis almost at the same time as the Rx led, but I read that this HW issue and doesn't influence the behaviour of the ethernet board. Is this correct? If not, how to resolve this?

Looking forward to hints and tips as I'm completely lost on this topic.