A simple sketch to demonstrate control of LED pixels via UDP.

UDPLED.ino

#include <EtherCard.h>
#include <IPAddress.h>
#include "FastSPI_LED2.h"
#define NUM_LEDS 8
#define DATA_PIN 6

CRGB pixels[NUM_LEDS];

// ethernet interface ip address
static byte myip[] = { 192,168,1,200 };
// gateway ip address
static byte gwip[] = { 192,168,1,254 };
// ethernet mac address - must be unique on your network
static byte mymac[] = { 0x70,0x69,0x69,0x2D,0x30,0x31 };

byte Ethernet::buffer[500]; // tcp/ip send and receive buffer

void udpSerialPrint(word port, byte ip[4], const char *data, word len) {
  if (len == NUM_LEDS * 3) {
    memcpy(pixels, data, len);
    FastLED.show();  
  }
}

void sendReady() {
  char collBuf[1];
  collBuf[0] = 0x75;
  static byte destIp[] = { 192,168,1,81 };
  ether.sendUdp((char*) collBuf, 1, 23456, destIp, 6000);
}

void sendRandom() {
  char collBuf[1];
  collBuf[0] = 0x75;
  static byte destIp[] = { 192,168,1,81 };
  ether.sendUdp("Random", 1, 23456, destIp, 6000);
}


void setup(){
  FastLED.addLeds<WS2812, DATA_PIN, GRB>(pixels, NUM_LEDS);
  Serial.begin(57600);
  Serial.println("\n[UDP Listener]");

  if (ether.begin(sizeof Ethernet::buffer, mymac) == 0)
    Serial.println( "Failed to access Ethernet controller");
  
  ether.staticSetup(myip, gwip);
  ether.printIp("IP:  ", ether.myip);
  ether.printIp("GW:  ", ether.gwip);

  ether.udpServerListenOnPort(&udpSerialPrint, 6000);
  sendReady();
}

void loop(){
  ether.packetLoop(ether.packetReceive());  
}