[SOLVED] Getting IP.. problem resolved

I had difficulties to get the IP address from the router at the start up of the Arduino.

The following helped:

I defined the Mac Adress of the Arduino in the setup:

byte mac[] = {
  0xDE, 0xAD, 0xBE, 0xEF, 0xFE, 0xED

In my router setup (TPLINK) I reserved one IP address for this MAC address.

No more problem.