File content as of revision 0:893f22e4a170:

#include "mbed.h"
#include "EthernetInterface.h"

#define ECHO_SERVER_PORT   23 // telnet defaults to port 23

DigitalOut myled(LED1);

// Initialize the Ethernet client library
EthernetInterface eth;

int main() {
    // Enter a MAC address for your controller below.
    uint8_t mac_addr[6] = {0x00, 0x08, 0xDC, 0x00, 0x01, 0x02}; 
    
    // initializing MAC address
    eth.init(mac_addr);

    // Check Ethenret Link
    if(eth.link() == true)
        printf("- Ethernet PHY Link-Done \r\n");
    else
        printf("- Ethernet PHY Link- Fail\r\n");

    // Start Ethernet connecting: Trying to get an IP address using DHCP
    if ( eth.connect() < 0 )
        printf("Fail - Ethernet Connecing");
    else
    {
        // Print your local IP address:
        printf("IP=%s\n\r",eth.getIPAddress());
        printf("MASK=%s\n\r",eth.getNetworkMask());
        printf("GW=%s\n\r",eth.getGateway());
    }        

    TCPSocketServer server;
    server.bind(ECHO_SERVER_PORT);
    server.listen();
    
    while (true) {
        printf("\nWait for new connection...\r\n");
        TCPSocketConnection client;
        server.accept(client);
        //client.set_blocking(false, 1500); // Timeout after (1.5)s
        
        printf("Connection from: %s\r\n", client.get_address());
        char buffer[256];
        while (true) {
            int n = client.receive(buffer, sizeof(buffer));
            if (n <= 0) break;
            
            // print received message to terminal
            buffer[n] = '\0';
            printf("Received message from Client :'%s'\r\n",buffer);
            
            // reverse the message
            char temp;
            for(int f = 0, l = n-1; f<l; f++,l--){
                temp = buffer[f];
                buffer[f] = buffer[l];
                buffer[l] = temp;
                }
            
            // print reversed message to terminal
            printf("Sending message to Client: '%s'\r\n",buffer);
            
            // Echo received message back to client
            client.send_all(buffer, n);
            if (n <= 0) break;
        }
        
        client.close();
        
        //led blinky
        myled = 1;
        wait(0.2);
        myled = 0;
        wait(0.2);
    }
}