Winsock programming using msdn PING sample code

To check to see if a pc is on your network you should us a udp ICMP_ECHO packet.

Here is a sample:
// EEPing.cpp : Defines the entry point for the console application.
//

#include "stdafx.h"
#include <atlbase.h>
#include "WINSOCK.H"
#include <comdef.h>                                                                        //add _bstr_t
#define   WINSOCK_VERSION               0x0101                 // program requires winsock version 1.1


#define   NO_FLAGS                      0                      // ping var
#define   ICMP_ECHO                     8                      // ping var
#define   ICMP_ECHO_REPLY               0                      // ping var
#define   ICMP_HEADER_SIZE              8                      // ping var
#define   ICMP_DATA                     "My Data"              // ping var
#define   PING_TIME_OUT                 4000                   // ping var
struct icmp
{
    BYTE icmp_type;
    BYTE icmp_code;
    WORD icmp_cksum;
    WORD icmp_id;
    WORD icmp_seq;
    BYTE icmp_data[1];
};
struct icmp     *pIcmpHeader;


WORD InternetChksum(LPWORD lpwIcmpData, WORD wDataLength);

int main(int argc, char* argv[])
{
    WSADATA           wsaData;
    int                 nRes            = 0;
    int             iPacketSize     = 0;
    int             iSentBytes      = 0;
    int             iReceivedBytes  = 0;
    int             iHostAddrLength = 0;
    int             iError          = 0;
    int             iOptValue       = 0;
    int             period          = 46;
    unsigned int    socketproto     = 0;
    PDWORD          pdwTimeStamp    = NULL;
    DWORD           dwReturnTime    = 0;
    DWORD           dwRoundTrip     = 0;
    BYTE            IcmpSendPacket[128];
    BYTE            IcmpRecvPacket[128];
    SOCKET          socketID        = 0;
    SOCKADDR_IN     sockAddrLocal;
    SOCKADDR_IN     sockAddrHost;
    IN_ADDR         inaddr;
    WCHAR*          wdest           = NULL;
      _bstr_t         m_PrimaryServer;
      struct hostent* m_PrimaryHost      = NULL;              // host struct for ping

    USES_CONVERSION;

      // set this var to name or ip address.
      // change this next var for the pcname or ip address you are trying to check on.
      m_PrimaryServer = _T("PCName");

    // setup protocol
    socketproto = IPPROTO_ICMP;

      //---------------------------
      // start up sockets
      //---------------------------
      nRes = WSAStartup (WINSOCK_VERSION, &wsaData);
    if(0 != nRes)
    {
        return (FALSE);
    }

    //---------------------------------
      // get hostinfo for m_PrimaryServer
    //---------------------------------
    if(!m_PrimaryHost)
    {
        // check to see if we have an ip address..
        wdest = wcsrchr(OLE2W(m_PrimaryServer), period);
        if(NULL == wdest)
        {
            //lookup computer name ie OS2NetDiagServer,OS2NetDiagServ02,......
              m_PrimaryHost = gethostbyname(m_PrimaryServer);
            //CheckSocket(_T(__FILE__), __LINE__, _T("gethostbyname - Failed"));
        } else {
            // lookup aaa.bbb.ccc.ddd (ip Address)
            inaddr.S_un.S_addr  = inet_addr(OLE2CA(m_PrimaryServer));
            m_PrimaryHost = gethostbyaddr((char *) &inaddr, 4, PF_INET);    
            //CheckSocket(_T(__FILE__), __LINE__, _T("gethostbyaddr - Failed"));
        }
    }

    //---------------------------------------------------
      // if hostinfo lookup for m_PrimaryServer failed exit
    //---------------------------------------------------
      if(!m_PrimaryHost)
      {
        //_Module.m_pDCap->DCPrintf(TRACE_INT_FUNC, TRACE_LEVEL1,
        //   _T("---- (gethostby[%s] lookup Failed)"), OLE2W(m_PrimaryServer));
        return FALSE;
    }

      // setup local address
      sockAddrLocal.sin_family = AF_INET;
    sockAddrLocal.sin_addr   = *((LPIN_ADDR) *m_PrimaryHost->h_addr_list);

    //------------------
    // Create Socket
    //------------------
    if(INVALID_SOCKET == (socketID = socket(PF_INET, SOCK_RAW, socketproto)))
    {
        //CheckSocket(_T(__FILE__), __LINE__, _T("socket create - Failed"));
        return FALSE;
    }

    //---------------------
    // Set Receive Time out
    //---------------------
    if (SOCKET_ERROR == setsockopt (socketID, SOL_SOCKET, SO_RCVTIMEO, (char*)&(iOptValue = PING_TIME_OUT), sizeof(int)) )
    {
        //CheckSocket(_T(__FILE__), __LINE__, _T("setsockopt - Failed"));
        closesocket(socketID);    
        return FALSE;
    }

    //----------------------------
    // Setup ICMP Header and Data
    //----------------------------
    pIcmpHeader = (struct icmp *) IcmpSendPacket;
    pIcmpHeader->icmp_type  = ICMP_ECHO;
    pIcmpHeader->icmp_code  = 0;
    pIcmpHeader->icmp_id    = 0;
    pIcmpHeader->icmp_seq   = 0;
    pIcmpHeader->icmp_cksum = 0;          

    //put tick count in the optional data area
    pdwTimeStamp = (PDWORD)&IcmpSendPacket[ICMP_HEADER_SIZE];
    *pdwTimeStamp =  GetTickCount();

      // copy echo data into packet
    memcpy(&IcmpSendPacket[ICMP_HEADER_SIZE + sizeof(DWORD)], ICMP_DATA, strlen(ICMP_DATA));
      iPacketSize = ICMP_HEADER_SIZE + sizeof(DWORD) + strlen(ICMP_DATA);

    // calc checksum and store it in the icmp_cksum
    pIcmpHeader->icmp_cksum = InternetChksum((LPWORD) pIcmpHeader, iPacketSize);

    if(pIcmpHeader->icmp_cksum != 0)
    {
        //----------------------
        // Send Ping to Primary
        //----------------------
        iSentBytes = sendto (socketID, (LPSTR)IcmpSendPacket, iPacketSize, NO_FLAGS, (LPSOCKADDR) &sockAddrLocal, sizeof(sockAddrLocal));
        if(SOCKET_ERROR == iSentBytes)
        {
            // sento error
            //CheckSocket(_T(__FILE__), __LINE__, _T("sendto - Failed"));
            closesocket(socketID);    
            return FALSE;
        }
        if(iSentBytes != iPacketSize)
        {
            // wrong number of bytes sent error
            //CheckSocket(_T(__FILE__), __LINE__, _T("sendto - Failed (SentBytes != PacketSize)"));
            closesocket(socketID);    
            return FALSE;
        }

        iHostAddrLength = sizeof(sockAddrHost);

        //------------------------
        // Recv Ping from Primary
        //------------------------
        iReceivedBytes = recvfrom(socketID, (LPSTR) IcmpRecvPacket, sizeof(IcmpRecvPacket), NO_FLAGS, (LPSOCKADDR) &sockAddrHost, &iHostAddrLength);
        if( SOCKET_ERROR == iReceivedBytes)
        {
            // Error recvfrom primary
            // don't display datacap here because it will print out over and over
            // until the primary comes back on line.
            closesocket(socketID);                  
            return FALSE;
        }
    } else {
       // check sum error
       //_Module.m_pDCap->DCPrintf(TRACE_INT_FUNC, TRACE_LEVEL1,
       //    _T("---- CNCREventLoggingDcomService::ConnectHeartBeatPing(InternetChksum Failed)"));
    }

    closesocket(socketID);                  

    dwReturnTime = GetTickCount();
    dwRoundTrip = dwReturnTime - *pdwTimeStamp;


      // clean up winsock
      WSACleanup();

    return TRUE;
}


WORD InternetChksum(LPWORD lpwIcmpData, WORD wDataLength)
{
    long lSum;
    WORD wOddByte;
    WORD wAnswer;

    lSum = 0L;
    while( wDataLength > 1 )
    {
        lSum += *lpwIcmpData++;
        wDataLength -= 2;
    }

    // Handle the odd byte if necessary and make sure the top half is zero
    if(wDataLength == 1)
    {
        wOddByte = 0;
        *((LPBYTE) &wOddByte) = *(LPBYTE)lpwIcmpData; // one byte only
        lSum += wOddByte;
    }

    // Add Back the carry outs from the 16 bits to the low 16 bits
    lSum = (lSum >> 16) + (lSum & 0xffff); // add high-16 to low-16
    lSum += (lSum >> 16);                  // add carry
    wAnswer = (WORD)~lSum;                 // 1's complement , then
                                           // truncate to 1 bits
    return(wAnswer);
}