SO_KEEPALIVE usage

Hello,

I am running a tcp socket server on TM4C129EXL LP and also have multiple LabVIEW tcp clients to communicate with it. I have a router with dhcp enabled ( uC is in auto obtain IP address). 

I would like to prepare server side code is to detect if any client is disconnected but not in a conventional way. I mean link layer failure of if the client is out of wifi range and so on. 

I made some tests to detect client side connection loss, such as ethernet cable removal btw. the uC and the router, but the following code:

bytesSent = send(clientfd,tcpPacket,HCOM_PACKET_SIZE_1024,0);

executes without any error, bytesSent is a valid number. I read about SO_KEEPALIVE that may help : 

Here is my server side code:

void tcpHandler(UArg arg0, UArg arg1)
{

    int                status;
    int                clientfd;
    int                server;
    struct sockaddr_in localAddr;
    struct sockaddr_in clientAddr;
    int                optval;
    int                optlen = sizeof(optval);
    socklen_t          addrlen = sizeof(clientAddr);
    Task_Handle        taskHandle;
    Task_Params        taskParams;
    Error_Block        eb;

    server = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
    if (server == -1) {
        System_printf("Error: socket not created.\n");
        goto shutdown;
    }


    memset(&localAddr, 0, sizeof(localAddr));
    localAddr.sin_family = AF_INET;
    localAddr.sin_addr.s_addr = htonl(INADDR_ANY);
    localAddr.sin_port = htons(arg0);

    status = bind(server, (struct sockaddr *)&localAddr, sizeof(localAddr));
    if (status == -1) {
        System_printf("Error: bind failed.\n");
        goto shutdown;
    }

    status = listen(server, NUMTCPWORKERS);
    if (status == -1) {
        System_printf("Error: listen failed.\n");
        goto shutdown;
    }

    // Set KEEPALIVE option to 1
    optval = 1;
    if (setsockopt(server, SOL_SOCKET, SO_KEEPALIVE, &optval, optlen) < 0)
    {
        System_printf("Error: setsockopt failed\n");
        goto shutdown;
    }


    if(getsockopt(server, SOL_SOCKET, SO_KEEPALIVE, &optval, &optlen) < 0)
    {
    	System_printf("Error: setsockopt failed\n");
		goto shutdown;
    }
    System_printf("Keepalive value: %d\r\n",optval);
    System_flush();


    while ((clientfd = accept(server, (struct sockaddr *)&clientAddr, &addrlen)) != -1)
    {
        System_printf("tcpHandler: Creating thread clientfd = %d\n", clientfd);

        /* Init the Error_Block */
        Error_init(&eb);

        Mailbox_Handle clientmb = lockMailbox();

        if(clientmb == NULL)
        {
        	System_printf("Unable to get mailbox\r\n");
        }

        /* Initialize the defaults and set the parameters. */
        Task_Params_init(&taskParams);
        taskParams.arg0 = (UArg)clientfd;
        taskParams.arg1 = (UArg) clientmb;
        //taskParams.arg1 = (UArg)TCP_Mailbox_Transmit;				// here we use the static mailbox created in XCONF
        taskParams.priority = 1;
        taskParams.stackSize = 2048;

        taskHandle = Task_create((Task_FuncPtr)TCP_Receive_Task, &taskParams, &eb);
        if (taskHandle == NULL)
        {
            System_printf("Error: Failed to create new Task\n");
            System_flush();
            close(clientfd);
        }

        taskParams.stackSize = 4096;
        taskHandle = Task_create((Task_FuncPtr)TCP_Transmit_Task, &taskParams, &eb);
		if (taskHandle == NULL)
		{
			System_printf("Error: Failed to create new Task\n");
			System_flush();
			close(clientfd);
		}

        /* addrlen is a value-result param, must reset for next accept call */
        addrlen = sizeof(clientAddr);

        System_flush();


    }

    System_printf("Error: accept failed.\n");

shutdown:
    if (server > 0) {
        close(server);
    }


}

When I start the server with wireshark I don't see any keepalive message btw the nodes. In the ndk\inc\stack\inc\resif.h I made the following changes:

#define DEF_TCP_KEEP_IDLE           600//72000   /* 2 hours */
#define DEF_TCP_KEEP_INTVL          750     /* 75 seconds */
#define DEF_TCP_KEEP_MAXIDLE        600//6000    /* 10 minutes */

But doen't have any effect on keepalive. 

My question is what is the proper way to use keepalive and how to configure the IDLE,INTVL,etc. values?