Сетевой адрес           Маска сети      Адрес шлюза       Интерфейс  Метрика
        238.1.1.0    255.255.255.0         On-link       192.168.0.2     11

#include <winsock2.h>
#include <Ws2tcpip.h> // для IP_MULTICAST_TTL
#include <conio.h>
#include <iostream>

using namespace std;



#define ERROR_HANDLER( OBJ ) {  cout << #OBJ << (OBJ) << endl;  exit(- 1 );  }


#define WSA_LAST_ERROR_HANDLER { \
	DWORD dw = WSAGetLastError(); \
	if ( NO_ERROR != dw ) { \
		char *MsgBuf; \
		FormatMessageA( FORMAT_MESSAGE_ALLOCATE_BUFFER | FORMAT_MESSAGE_FROM_SYSTEM,  0 , dw,  0 , (LPSTR) &MsgBuf,  0 ,  0  ); \
		cout << dw << ' ' << MsgBuf << endl; \
		exit(- 1 ); \
	} \
}



#pragma comment( lib, "Ws2_32.lib" )



int main() {

	const bool flgSender = false;

	WSADATA WSAData;
	int ErrCode = WSAStartup( MAKEWORD(  2 ,  2  ), &WSAData );
	if (  0  != ErrCode ) ERROR_HANDLER( ErrCode );


	SOCKET s = WSASocket( AF_INET, SOCK_DGRAM, IPPROTO_UDP,  0 ,  0 , WSA_FLAG_MULTIPOINT_C_LEAF | WSA_FLAG_MULTIPOINT_D_LEAF );
	if ( INVALID_SOCKET  == s ) WSA_LAST_ERROR_HANDLER;

	sockaddr_in local;
	memset( &local,  0 , sizeof( local ) );
	local.sin_family = AF_INET;
	local.sin_addr.s_addr = inet_addr( "127.0.0.1" );
	local.sin_port = htons( flgSender ?  5678  :  5679  );

	if (  0  !=  bind( s, (sockaddr*) &local, sizeof( local ) ) ) WSA_LAST_ERROR_HANDLER;

	int optval =  8 ;
	if (  0  != setsockopt( s, IPPROTO_IP, IP_MULTICAST_TTL, (char*) &optval, sizeof( optval ) ) ) WSA_LAST_ERROR_HANDLER;


	sockaddr_in remote;
	memset( &remote,  0 , sizeof( remote ) );
	remote.sin_family = AF_INET;
	remote.sin_addr.s_addr = inet_addr( "238.1.1.1" );
	remote.sin_port = htons(  5680  );

	SOCKET sR = WSAJoinLeaf( s, (sockaddr*) &remote, sizeof( remote ),  0 ,  0 ,  0 ,  0 , JL_BOTH );
	if ( INVALID_SOCKET == sR ) WSA_LAST_ERROR_HANDLER;
	if ( s != sR ) ERROR_HANDLER( sR );


	// Цикл отправки / получения сообщений
	int i;

	WSABUF Buffer;
	Buffer.len = sizeof( i );
	Buffer.buf = (CHAR*) &i;

	if ( flgSender ) {
		for ( i =  0 ; ! _kbhit(); i++ ) {
			DWORD NumberOfBytesSent =  0 ;
			if (  0  != WSASendTo( s, &Buffer,  1 , &NumberOfBytesSent,  0 , (sockaddr*) &remote, sizeof( remote ),  0 ,  0  ) ) WSA_LAST_ERROR_HANDLER;
			cout << i << endl;
			Sleep(  1000  );
		}
	}
	else {
		for ( ; ! _kbhit(); ) {
			DWORD NumberOfBytesRecvd =  0 , Flags =  0 ;
			sockaddr_in From;
			memset( &From,  0 , sizeof( From ) );
			INT Fromlen = sizeof( From );
			if (  0  != WSARecvFrom( s, &Buffer,  1 , &NumberOfBytesRecvd, &Flags, (sockaddr*)&From, &Fromlen,  0 ,  0  ) ) WSA_LAST_ERROR_HANDLER;
			cout << i << endl;
		}
	}


	if (  0  != closesocket( s ) ) WSA_LAST_ERROR_HANDLER;

	if (  0  != WSACleanup() ) WSA_LAST_ERROR_HANDLER;

	return  0 ;
}