멀티캐스트에 대한 질문입니다.

간단한 멀티캐스트 샘플을 제작중인데요.
같은 라우터 안에서 테스트를 하면 데이터를 잘받아오는데
외부에서는 데이터를 받아오지를 못합니다. 주소는 225.100.100.1을
사용하였고 TTL 값은 255 를 사용했거든요. 소스를 첨부하니 무슨
문제가 있는 알려주시면 감사드리겠습니다.

데이타를 보내는 쪽

#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <arpa/inet.h>
#include <netinet/in.h>

int main()
{
	int sock, dummy, count = 0;
	struct sockaddr_in multicastAddr;
	char sendString[255];
	unsigned char multicastTTL;
	unsigned int sendStringLen;

	multicastTTL = 255;
	sock = socket( AF_INET, SOCK_DGRAM, IPPROTO_UDP );
	if( sock < 0 )
		return -1;
	dummy = setsockopt( sock, IPPROTO_IP, IP_MULTICAST_TTL, (void *) &multicastTTL, sizeof( multicastTTL ) );
	if( dummy < 0 )
		return -1;

	memset( &multicastAddr, 0, sizeof( multicastTTL ) );
	multicastAddr.sin_family = AF_INET;
	multicastAddr.sin_addr.s_addr = inet_addr( "225.100.100.1" );
	multicastAddr.sin_port = htons( 6000 );

	dummy = connect( sock, (struct sockaddr *) &multicastAddr, sizeof( multicastAddr ) );
	if( dummy < 0 )
		return -1;

	for( ;; )
	{
		memcpy( sendString, &count, sizeof( int ) );
		sendStringLen = strlen( sendString );
		dummy = write( sock, sendString, sendStringLen );
		if( dummy == sendStringLen )
		count++;
		usleep(100);
	}

	return 0;
}

데이타를 받는 쪽

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <arpa/inet.h>
#include <netinet/in.h>

#define MAXRECVSTRING 255

int main()
{
	int sock = 0, 
		dummy = 0, 
		count = 0, 
		before = 0,
		all = 0,
		complete = 0,
		error = 0;
	float per = 0;	
	struct sockaddr_in multicastAddr;
	char recvString[MAXRECVSTRING+1];
	int recvStringLen = 0;
	struct ip_mreq multicastRequest;
	
	sock = socket( AF_INET, SOCK_DGRAM, IPPROTO_UDP );
	if( sock < 0 )
		return -1;
	memset( &multicastAddr, 0, sizeof( multicastAddr ) );
	multicastAddr.sin_family = AF_INET;
	multicastAddr.sin_addr.s_addr = htonl( INADDR_ANY );
	multicastAddr.sin_port = htons( 6000 );

	dummy = bind( sock, (struct sockaddr *) &multicastAddr, sizeof( multicastAddr ) );
	if( dummy < 0 )
		return -1;

	multicastRequest.imr_multiaddr.s_addr = inet_addr( "225.100.100.1" );
	multicastRequest.imr_interface.s_addr = htonl( INADDR_ANY );
	dummy = setsockopt( sock, IPPROTO_IP, IP_ADD_MEMBERSHIP, (void *) &multicastRequest, sizeof( multicastRequest ) );
	if( dummy < 0 )
		return -1;
	
	while(1)
	{
		recvStringLen = recvfrom( sock, recvString, MAXRECVSTRING, 0, NULL, 0 );
		if( recvStringLen < 0 )
			return -1;
		all++;
		memcpy( &count, recvString, sizeof( int ) );
		if( ( before + 1 ) != count )
		{
			error++;
			per = (float )complete / all;
			printf( "%d \t %d \t %d \t %.5f\n", all, complete, error, per );
		}
		else
		{
			complete++;
		}
		
		before = count;
	}

	return 0;
}