include the mbed library with this snippet

#include "mbed.h"
#include "rtos.h"
#include "EthernetInterface.h"
#include "USBSerial.h"

#define LOCAL_ADDR  "195.0.0.6"
#define MASK        "255.255.255.0"
#define GATEWAY     "195.0.0.1"
#define PORT        4323

DigitalOut gLED1(LED1, 1);
DigitalOut gLED2(LED2, 1);
DigitalOut gLED3(LED3, 1);
DigitalOut gLED4(LED4, 1);
EthernetInterface gEth;
UDPSocket gSocket;

void CmdThread(const void * arg);
void HeartBeat(const void * arg);

extern "C" void mbed_mac_address(char *s);

Thread* gThreadCmd;
Thread* gThreadHeartBeat;
Timer gSysTimer;

int main() 
{
    puts("Starting\r\n");
    
    gSysTimer.start();

    puts("gEth.init\r\n");
    
    if (gEth.init(LOCAL_ADDR, MASK, GATEWAY) < 0)
    {
        error("FATAL Error: Ethernet Initialization Error\r\n");
    }

    puts("gEth.connect\r\n");
    
    if (gEth.connect(30000) < 0)
    {
        error("FATAL Error: Ethernet Connection Error\r\n");
    }
    
    puts("gSocket.bind\r\n");
    
    if (gSocket.bind(PORT))
    {
        error("FATAL Error: Unable to bind ALXT_MSG_PORT socket");
    }

    gSocket.set_broadcasting(true);
    gSocket.set_blocking(false, 2500);
    
    puts("Go!\r\n");

    Endpoint source;

    gThreadHeartBeat = new Thread(HeartBeat, NULL, osPriorityLow, DEFAULT_STACK_SIZE, NULL);

    gThreadCmd = new Thread(CmdThread, NULL, osPriorityLow, DEFAULT_STACK_SIZE*10, NULL);

    unsigned char receiveBuf[2048];
    
    while(1) 
    {
        int count = 0;
        
        count = gSocket.receiveFrom(source, (char*)receiveBuf, sizeof(receiveBuf));
        
        if (count == 0)
        {
            gLED4 = !gLED4.read();
        }
        else
        {
            printf("Recvd %d bytes from %s\r\n", count, source.get_address());
            gLED2 = !gLED2.read();
        }
    }
}

void HeartBeat(const void * arg)
{
    while (true)
    {
        gLED1 = !gLED1.read();
        gThreadHeartBeat->wait(250);
    }
}

void CmdThread(const void * arg)
{
    char cmdBuffer[256] = {0};
    unsigned int cmdBufferIndex = 0;
    char cmdChar;
    char cmd;
    USBSerial serial;
    char mac[6];

    while (true)
    {
        cmdChar = serial._getc();

        if (cmdChar == '\r')
        {
            cmd = cmdBuffer[0];

            switch(cmd)
            {
                case 'M':

                    mbed_mac_address(mac);

                    char macAddr[20];

                    sprintf(macAddr, "%02x:%02x:%02x:%02x:%02x:%02x", mac[0], mac[1], mac[2], mac[3], mac[4], mac[5]);

                    serial.printf("%c %s\r\n", cmd, macAddr);
                    break;

                default:
                    serial.printf("%c -1 \"Command <%s> is not valid\"\r\n", cmd, cmdBuffer);
                    break;
            }

            memset(cmdBuffer, 0, sizeof(cmdBuffer));
            cmdBufferIndex = 0;
        }
        else
        {
            if (cmdChar != '\n' && cmdBufferIndex < sizeof(cmdBuffer))
            {
                cmdBuffer[cmdBufferIndex++] = cmdChar;
            }
            else if (cmdBufferIndex >= sizeof(cmdBuffer))
            {
                ;
            }
        }
    }
}