Issue with multicast when socket isn't bound to INADDR_ANY

[Clairvoyant1332]

If I create a socket bound to INADDR_ANY, then bind to a multicast address (say 230.4.4.1) on one or more interfaces (say 192.168.1.1 and 192.168.2.1), that socket will receive packets sent to 230.4.4.1 that are received on either 192.168.1.1 or 192.168.2.1 as expected.

However, if I create a socket bound to a specific address (say 192.168.1.1), then bind to multicast address 230.4.4.1) on 192.168.1.1 and 192.168.2.1, that socket will NOT receive packets sent to 230.4.4.1 that are received on 192.168.1.1.

This happens on Linux 2.6 and Solaris 10 but not Windows XP. Under XP, multicast works whether I bind the socket to INADDR_ANY or a specific address.

Anyone come across this before? Any idea how to fix it?

[Clairvoyant1332]

Here's some code that demos the problem:

The receiver:

#include <sys/socket.h>
#include <stdio.h>
#include <stdlib.h>
#include <netinet/in.h>
#include <strings.h>

int sock;

int main(int argc, char *argv[])
{
  int addr_len;
  struct sockaddr_in sin,sin_recv;
  struct ip_mreq multi;
  char mes[255];

  bzero(&sin,sizeof(sin));
  multi.imr_multiaddr.s_addr=inet_addr("230.4.4.1");
  multi.imr_interface.s_addr=inet_addr("192.168.1.6");  // Fill in with your local IP
  sin.sin_family = AF_INET;
  // With this line uncommented, it works
  //sin.sin_addr.s_addr=INADDR_ANY;
  // With this line uncommented, it doesn't work
  sin.sin_addr.s_addr=inet_addr("192.168.1.6");  // Fill in with your local IP
  sin.sin_port = htons(1044);
  if ((sock=socket(AF_INET,SOCK_DGRAM,0))==-1) {
    perror("Error creating socket");
    exit(1);
  }
  if (bind(sock,(struct sockaddr *)&sin,sizeof(sin))==-1) {
    perror("Error binding socket");
    close(sock);
    exit(1);
  }
  if (setsockopt(sock,IPPROTO_IP,IP_ADD_MEMBERSHIP,(char *)&multi,sizeof(multi))== -1) {
    perror("Error joining multicast group");
    close(sock);
    exit(1);
  }
  while (1) {
    bzero(mes,sizeof(mes));
    bzero(&sin_recv,sizeof(sin_recv));
    addr_len=sizeof(sin_recv);
    printf("Waiting for packet...\n");
    if (recvfrom(sock,mes,sizeof(mes),0,(struct sockaddr *)&sin_recv,&addr_len)==-1) {
      perror("error recving socket");
      close(sock);
      exit(1);
    }
    printf("Got packet\n");
    printf("Origin: %s port %d\n",inet_ntoa(sin_recv.sin_addr),sin_recv.sin_port);
    printf("Message: %s\n",mes);
  }
  return 0;
}

The sender:

#include <sys/socket.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <netinet/in.h>
#include <string.h>
#include <strings.h>

int sock;

int main(int argc, char *argv[], char *envp[])
{
  struct sockaddr_in sin;
  struct in_addr out_addr;
  char mes[255], ttl;
  int c;

  ttl=1;
  out_addr.s_addr=htonl(INADDR_ANY);
  while ((c = getopt(argc, argv, "t:I:")) != EOF)
    switch (c) {
    case 't':
      ttl=optarg[0];
      break;
    case 'I':
      if (inet_addr(optarg)!=-1)
        out_addr.s_addr=inet_addr(optarg);
      break;
    case '?':
      printf("Unknown option: %s\n",optarg);
      break;
    }
  argc-=optind;
  argv+=optind;
  printf("Enter message: ");
  fgets(mes,sizeof(mes),stdin);
  bzero(&sin,sizeof(sin));
  sin.sin_family=AF_INET;
  sin.sin_addr.s_addr=inet_addr(argv[0]);
  sin.sin_port=htons(atoi(argv[1]));
  if ((sock=socket(AF_INET,SOCK_DGRAM,0))==-1) {
    perror("Error creating socket");
    exit(1);
  }
  if (setsockopt(sock,IPPROTO_IP,IP_MULTICAST_TTL,(char *)&ttl,sizeof(ttl))== -1) {
    perror("Error setting ttl");
    close(sock);
    exit(1);
  }
  if (setsockopt(sock,IPPROTO_IP,IP_MULTICAST_IF,(char *)&out_addr,sizeof(out_addr))== -1) {
    perror("Error setting outgoing interface");
    close(sock);
    exit(1);
  }
  if (sendto(sock,mes,strlen(mes),0,(struct sockaddr *)&sin,sizeof(sin))==-1) {
    perror("Send error");
  }
}