EthernetUDP.parsePacket()

// An EthernetUDP instance to let us send and receive packets over UDP
EthernetUDP Udp;

Udp.parsePacket();

#include <Ethernet.h>
#include <EthernetUdp.h>
 
// Enter an IP address for your controller below.
// The IP address will be dependent on your local network:
IPAddress ip(192, 168, 1, 177);
 
unsigned int localPort = 8888;      // local port to listen on
 
// An EthernetUDP instance to let us send and receive packets over UDP
EthernetUDP Udp;
 
void setup() {
  // start the Ethernet and UDP:
  Ethernet.begin(NULL,ip);
  Udp.begin(localPort);
 
  Serial.begin(9600);
}
 
void loop() {
  // if there's data available, read a packet
  int packetSize = Udp.parsePacket();
  if(packetSize)
  {
    Serial.print("Received packet of size ");
    Serial.println(packetSize);
  }
  delay(10);
}