ethernet_wo_sd_mkr.ino

#include <SPI.h>
#include <Ethernet.h>

void setup() {
  /* https://www.arduino.cc/en/Guide/MKRETHShield
   * As the W5500 and SD card share the SPI bus, 
   * only one at a time can be active. 
   * If you are using both peripherals in your program, this should be taken care of by the corresponding libraries. 
   * If you're not using one of the peripherals in your program, however, you'll need to explicitly deselect it. 
   * To do this with the SD card, set pin 4 as an output and write a high to it. 
   * For the W5500, set digital pin 5 as a high output.
   */
  pinMode(4, OUTPUT);
  digitalWrite(4, HIGH);
  
  Ethernet.init(5);   // MKR ETH shield
  // ....
}