Usage of SIOCADDMULTI ?

Im trying to grab some ethernet multicasts. And the ioctl that should do that is SIOCADDMULTI.
But I can't get it to work. And I have not found any who use that from userlevel so
this is my guess who to do it. (I don't work but dont gives any error message)

#include        <stdio.h>
#include        <sys/ioctl.h>
#include        <net/if.h>
#include        <arpa/inet.h>
#include        <errno.h>
#include        <sys/un.h>

int main()
{
int i,res,sock,from_len;
struct sockaddr_in eb_addr,from_addr;
char databuf[1500];
struct ifreq req;

  if((sock = socket(AF_INET, SOCK_DGRAM, 0)) == -1)
    {
      printf("%s",strerror(errno));
      exit(1);
    }

  eb_addr.sin_family      = AF_INET;
  /*    eb_addr.sin_family      = AF_UNSPEC; */
  eb_addr.sin_addr.s_addr = inet_addr("0.0.0.0");
  eb_addr.sin_port        = htons(4711);

for (i = 0; i < 8; ++i)

    eb_addr.sin_zero[i] = 0;
  if(bind(sock,(struct sockaddr*)  &eb_addr, sizeof(struct sockaddr_in))
== -1)
    {
      printf("Unable to bind the socket\n");
      exit(1);
    }
  strcpy(req.ifr_name,"eth0");
  req.ifr_ifru.ifru_addr.sa_data[0] = 0x01;
  req.ifr_ifru.ifru_addr.sa_data[1] = 0x80;
  req.ifr_ifru.ifru_addr.sa_data[2] = 0xc2;
  req.ifr_ifru.ifru_addr.sa_data[3] = 0x00;
  req.ifr_ifru.ifru_addr.sa_data[4] = 0x00;
  req.ifr_ifru.ifru_addr.sa_data[5] = 0x00;
  /* req.ifr_flags = IFF_ALLMULTI;   | IFF_PROMISC;  */
  res = ioctl(sock,SIOCADDMULTI,&req);
  if(res == -1)
    {
    printf("%s",strerror(errno));
    exit(1);

}

while (1)

    {
      printf("enter recvfrom\n");
      res = recvfrom(sock,  databuf, sizeof(databuf), 0,(struct
sockaddr*) &from_addr, &from_len);
      printf("Received %d bytes\n", res );
    }

return 0;
}

This on a 2.4.9 kernel on SMP P2. Im trying to grab some 802 bridge packets and I see them
with tcpdump but that is using a other interface. (BPF or what ever) Any ideas whats wrong ?

According to ip(7) you should use setsockopt, the following works for me (PS: I'm running 2.4.3 and I get EPERM as non root and EINVAL as root when running your code.)

#include <net/if.h>
#include <netinet/in.h>
#include <stdio.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/ioctl.h>
#include <netdb.h>

#define ASSERT(a, op, b, m...) do { if ( a op b) { \
fprintf(stderr, "ASSERT (" #a " " #op " " #b ") at %s line %d:", __FILE__, __LINE__); \
fprintf(stderr, m);\
fprintf(stderr, "\n"); \
fflush(stderr); exit(-1); }} while(0)

struct ifreq ir;
struct ip_mreq mr;

int createmcast()
{
int s, rc;
struct hostent * he;
struct sockaddr_in to;

  s = socket(AF_INET, SOCK_DGRAM, 0);

  ASSERT (s, == , -1, "socket failed errno=%d", errno);
  mr.imr_interface.s_addr = (in_addr_t) htonl(INADDR_ANY);

  to.sin_family = AF_INET;
  to.sin_port = 0;
  to.sin_addr.s_addr = htonl(INADDR_ANY);
  //  bind(s, &to, sizeof(struct sockaddr_in));

he = gethostbyname("172.16.0.116");
ASSERT (he, ==, NULL, "gethostbyname if failed %d", h_errno); // memcpy (&mr.imr_interface, &he->h_addr_list[0], sizeof (struct
sockaddr_in));

he = gethostbyname("225.0.0.100");
ASSERT (he, ==, NULL, "gethostbyname mc failed %d", h_errno); memcpy (&mr.imr_multiaddr, he->h_addr_list[0], sizeof (struct
sockaddr_in));
errno = 0;
printf ("%#x %#x\n", mr.imr_multiaddr.s_addr,
mr.imr_interface.s_addr);

rc = setsockopt (s, IPPROTO_IP, IP_ADD_MEMBERSHIP, &mr, sizeof(struct
ip_mreq));

ASSERT (rc, <, 0, "setsockopt (.., IPPROTO_IP, IP_ADD_MEMBERSHIP, ..)
failed errno=%d", errno);

rc = setsockopt (s, IPPROTO_IP, IP_MULTICAST_IF, &mr.imr_interface,
sizeof(struct in_addr));

ASSERT (rc, <, 0, "setsockopt (.., IPPROTO_IP, IP_MULTICAST_IF, ..)
failed errno=%d", errno);

return s;
};

int createudp()
{
int s, rc;
struct sockaddr_in to;
s = socket(AF_INET, SOCK_DGRAM, 0);

to.sin_family = AF_INET;
to.sin_port = htons(12345);
to.sin_addr.s_addr = htonl(INADDR_ANY);
rc = bind(s, &to, sizeof(struct sockaddr_in));
ASSERT (rc, ==, -1, "bind failed %d", errno);
return s;
};

int sendmcast (int s, char * payload, int plen)
{
int rc;
struct sockaddr_in to;

to.sin_family = AF_INET;
to.sin_port = htons(12345);
memcpy(&to.sin_addr, &mr.imr_multiaddr.s_addr, sizeof(struct
in_addr));

  if (plen == 0) plen = strlen(payload);

  rc = sendto (s,  payload, plen , 0, &to, sizeof(struct sockaddr_in));

  printf ("sendto returned %d\n", rc);
  ASSERT (rc, <, 0, "snndto () failed errno=%d", errno);

};

char * getdgram(int s)
{
struct sockaddr_in from;
int rc;
static char buffer[1024];
static char addrbuf[100];
socklen_t fromlen;

fromlen = sizeof(struct sockaddr_in);
rc = recvfrom(s, buffer, 1024, 0, &from, &fromlen); inet_ntop(AF_INET, &from.sin_addr, addrbuf, 100); printf ("from socket %d, we got a message %s sender %s:%d (%d)\n",

          s, buffer, addrbuf , ntohs(from.sin_port), fromlen);

return buffer;
};
main()
{
int ms, us;
int rc;

  ms = createmcast();
  us = createudp();

  sendmcast(us, "heihei", 0);

  sleep(3);
  getdgram(us);

  exit(0);

  //  rc = ioctl (s, SIOCGIFADDR, &ir);

//ASSERT (rc, <, 0, "ioctl failed errno=%d", errno);
};

Den 28 Aug 2001 22:56:10 +0200, skrev Peter Enderborg:

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Terje Eggestad                  [email protected]
Scali Scalable Linux Systems    http://www.scali.com

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