STATUS TCP_ClientConnect (char *serverName, int *soc_desc)
{
    struct sockaddr_in  serverAddr;    /* server's socket address */
    int                 sockAddrSize;  /* size of socket address structure */
    int                 sFd;           /* socket file descriptor */

    /* create client's socket */
    if ((sFd = socket (AF_INET, SOCK_STREAM, 0)) == ERROR)
    {
        //perror ("socket");
        printf ("SOCKET ERROR\n");
        return (ERROR);
    }

    /* bind not required - port number is dynamic */
    /* build server socket address */
    sockAddrSize = sizeof (struct sockaddr_in);
    bzero ((char *) &serverAddr, sockAddrSize);
    serverAddr.sin_family = AF_INET;
    serverAddr.sin_len = (u_char) sockAddrSize;
    serverAddr.sin_port = htons (SERVER_PORT_NUM);

    if (((int)(serverAddr.sin_addr.s_addr = inet_addr (serverName)) == ERROR) &&
        ((int)(serverAddr.sin_addr.s_addr = hostGetByName (serverName)) == ERROR))
    {
        printf ("UNKNOWN SERVER NAME\n");
        close (sFd);
        return (ERROR);
    }
    
    /* bind a port number to the socket */
    if (bind(sFd, (struct sockaddr *) &serverAddr, sizeof(serverAddr)) == ERROR)
    {
        printf("BIND ERROR\n");
        return (ERROR);
    }

    /* connect to server */
    if (connect (sFd, (struct sockaddr *) &serverAddr, sockAddrSize) != OK)
    {
        printf ("CONNECTION ERROR\n");
        close (sFd);
        return (ERROR);
    }
    
    *soc_desc = sFd;
    
    return (OK);
}

int socket_descriptor=0;
char *server_ip = "10.0.0.80";

void tSpectraTaskEntryPoint()
{
    
    if (TCP_ClientConnect(server_ip, &socket_descriptor)==ERROR)
     printf ("CLIENT CONNECT ERROR\n");
    else
    printf("CLIENT CONNECT OK descriptor = %d\n", socket_descriptor);
    
   SpectraMain();
}

STATUS TCP_ClientConnect (char *serverName, int *soc_desc)
{
    struct sockaddr_in  serverAddr;    /* server's socket address */
    int                 sockAddrSize;  /* size of socket address structure */
    int                 sFd;           /* socket file descriptor */

    /* create client's socket */
    if ((sFd = socket (AF_INET, SOCK_STREAM, 0)) == ERROR)
    {
        printf ("SOCKET ERROR\n");
        return (ERROR);
    }
    else
         printf ("SOCKET DESC = %d\n", sFd);

    /* bind not required - port number is dynamic */
    /* build server socket address */
    sockAddrSize = sizeof (struct sockaddr_in);
    bzero ((char *) &serverAddr, sockAddrSize);
    serverAddr.sin_family = AF_INET;
    serverAddr.sin_len = (u_char) sockAddrSize;
    serverAddr.sin_port = htons (SERVER_PORT_NUM);

    if (((int)(serverAddr.sin_addr.s_addr = inet_addr (serverName)) == ERROR) &&
        ((int)(serverAddr.sin_addr.s_addr = hostGetByName (serverName)) == ERROR))
    {
        printf ("UNKNOWN SERVER NAME\n");
        close (sFd);
        return (ERROR);
    }
    else
    {
        printf ("ADDR = %d\n", serverAddr.sin_addr.s_addr);
        printf ("PORT = %d\n", serverAddr.sin_port);
        
    }
    
    /* bind a port number to the socket */
    if (bind(sFd, (struct sockaddr *) &serverAddr, sizeof(serverAddr)) == ERROR)
    {
        printf("BIND ERROR\n");
        return (ERROR);
    }


    /* connect to server */
    if (connect (sFd, (struct sockaddr *) &serverAddr, sockAddrSize) != OK)
    {
        printf ("CONNECTION ERROR\n");
        close (sFd);
        return (ERROR);
    }
    
    *soc_desc = sFd;
    
    return (OK);
}

void SpectraMain()
{
    while (spectra_alive)
    {
        if (TCP_ClientRead(read_buf, socket_descriptor) != ERROR)
        {
            printf ("CLIENT RECIEVED MESSAGE\n");
            //echo back
            TCP_ClientWrite(read_buf, socket_descriptor);
        }
        else
        {
            TCP_ClientWrite("no message", socket_descriptor);
        }
            
        taskDelay(50);
    }
}

/* Set the option active */
   optval = 1;
   optlen = sizeof(optval);
   if(setsockopt(s, SOL_SOCKET, SO_KEEPALIVE, &optval, optlen) < 0) {
      perror("setsockopt()");
      close(s);
      exit(EXIT_FAILURE);
   }
   printf("SO_KEEPALIVE set on socket\n");

static int waittoread(int sock){
    fd_set fds, efds;
    struct timeval timeout;
    int rc;
    timeout.tv_sec = 1; // wait not more than 1 second
    timeout.tv_usec = 0;
    FD_ZERO(&fds);
    FD_ZERO(&efds);
    FD_SET(sock, &fds);
    FD_SET(sock, &efds);
    do{
        rc = select(sock+1, &fds, NULL, &efds, &timeout);
        if(rc < 0){
            if(errno != EINTR){
                putlog("Server not available");
                WARN("select()");
                return -1;
            }
            continue;
        }
        break;
    }while(1);
    if(FD_ISSET(sock, &efds)) return -1; // exception - socket closed
    if(FD_ISSET(sock, &fds))  return  1;
    return 0;
}

#if KEEPALIVE_ON
    /* Set the option active */
    optval = 1;
    optlen = sizeof(optval);
    if(setsockopt(sFd, SOL_SOCKET, SO_KEEPALIVE, &optval, optlen) < 0)
    {
        close(sFd);
        return (ERROR);
    }
    printf("SO_KEEPALIVE set on socket\n");
    
    /* Interval (in seconds) between keepalives */
    optval = 1;
    setsockopt(sFd, IPPROTO_TCP, TCP_KEEPINTVL, &optval, optlen);
    /* Maximum number of keepalives before dropping the connection */
    optval = 10;
    setsockopt(sFd, IPPROTO_TCP, TCP_KEEPCNT, &optval, optlen);
    /* Send first keepalive probe when the connections been idle this time (in seconds) */
    optval = 5;
    setsockopt(sFd, IPPROTO_TCP, TCP_KEEPIDLE, &optval, optlen);
    #endif

static int waittoread(int sock){
    fd_set fds, efds;
    struct timeval timeout;
    int rc;
    timeout.tv_sec = 1; // wait not more than 1 second
    timeout.tv_usec = 0;
    FD_ZERO(&fds);
    FD_ZERO(&efds);
    FD_SET(sock, &fds);
    FD_SET(sock, &efds);

     rc = select(sock+1, &fds, NULL, &efds, &timeout);
        if(rc < 0)
        {
                putlog("Server not available");
                return -1;
        }
        break;

    if(FD_ISSET(sock, &efds)) return -1; // exception - socket closed
    if(FD_ISSET(sock, &fds))  return  1;
    return 0;
}

mlen = read (soc_desc, read_buff, sizeof(read_buff));

recvfrom( )
recv( )
recvmsg( )

Пример:
  > arp -s 157.55.85.212   00-aa-00-62-c6-09  ... Добавляет статическую запись.
  > arp -a                                    ... Выводит ARP-таблицу.

//FIRST IP;
ifAddrSet ("ETH0","10.0.0.10");
ifMaskSet ("ETH0", 0xffffff00);
//SECOND IP
ifAddrAdd ("ETH0","192.168.101.100","192.168.101.255",0xffffff00);

struct sockaddr_in localaddr;
localaddr.sin_family = AF_INET;
localaddr.sin_addr.s_addr = inet_addr("192.168.1.100");
localaddr.sin_port = 0;  
bind(sockfd, (struct sockaddr *)&localaddr, sizeof(localaddr));

sudo gedit /etc/network/interfaces
И редактируешь его приводя к следующему виду:
auto eth0
iface eth0 inet static
  address 192.168.1.5
  netmask 255.255.255.0
  network 192.168.1.0
  broadcast 192.168.1.255
  gateway 192.168.1.1
  dns-nameservers 8.8.8.8 192.168.1.1

auto eth0:1
iface eth0:1 inet static
  address 192.168.0.5
  netmask 255.255.255.0
  network 192.168.1.0
  broadcast 192.168.1.255
  gateway 192.168.0.1
  hwaddress ether 00269ebba619 --------------------- это похоже на "виртуальный" MAC
  dns-nameservers 8.8.8.8 192.168.1.1