answer: IPv6 multicast sendto() 'operation not supported' on FreeBSD

[Donald.McLachlan at crc.ca]

Hello,

I found the "problem" with the code shown and can explain it as follows:

When binding a socket to a unicast address you are saying:

- "all received packets with the given unicast dest address and (UDP) port
   should be delivered to this socket"

- "and all packets sent from this socket must be sent with this unicast
   source address and (UDP) port".

The problem is that as written this code is saying the same thing (but
substituting unicast with multicast, ie:

- "all received packets with the given mulitcast dest address and (UDP) port
   should be delivered to this socket" [OK]

- "and all packets sent from this socket must be sent from this mulitcast
   source address and (UDP) port". [Strictly speaking this is wrong]

Multicast packets must be sent with a unicast source address!

- FreeBSD is being pedantic and is not allowing to send pkts with the source
  address specified in the bind().

- Linux and Solaris "know" this is not allowed, and send the packet using
  the unicast IP address of the outgoing interface as the source address
  (instead of the multicast address specified in the bind()).

QED.

[ hence ssetsockopt(IPV6_MULTICAST_IF) ? ]

Don


> From: Donald McLachlan <don at mainframe.dgrc.crc.ca>
> 
> Hello,
> 
  < snip >
> 
> In preparation for writing an IPv6 multicast application I wrote a little
> test program (shown below).  This program worked on linux (RedHat), but
> when I try it on a FreeBSD box (5.0, running zebra router and pim6dd)
> sendto() fails with "Operation not supported" ... ???
> 
> To verify my app was OK, I installed a solaris box on the LAN beside the
> linux box and the app compiled and worked fine.
> 
> Thinking it might be a bug in 5.0 or an interaction with zebra/pim6dd I
> installed a FreeBSD 5.2 box on the lan beside the other 2 app boxes and
> I get the same error again.  Anyone know what is missing/wrong in my test app?
> 
> [ I'm guessing FreeBSD wants some extra socket options set, but I don't know
>   which ones. ]
> 
> Thanks,
> Don
> 
> 
> 
> 
> /*
> 	mcast6.c
> */
> 
> #include <stdio.h>
> #include <sys/types.h>
> #include <sys/socket.h>
> #include <sys/time.h>
> #include <netinet/in.h>
> #include <arpa/inet.h>
> #include <netdb.h>
> #include <string.h>
> #include <strings.h>
> #include <unistd.h>
> #include <stdlib.h>
> #include <sys/wait.h>
> #include <net/if.h>
> 
> extern int errno;
> 
> void start_sender(int sock, struct sockaddr_in6 *sin);
> void start_listener(int sock);
> 
> int main(int argc, char *argv[])
> {
> 	int sock, hops;
> 	unsigned int ifindex;
> 	struct sockaddr_in6 sin;
> 	struct ipv6_mreq mreq;
> 	char ifname[IF_NAMESIZE];
> 
> 	static unsigned char the_addr[16];
> 
> 	inet_pton(AF_INET6, "ff05::abcd", the_addr);
> 
> 	if ((sock=socket(AF_INET6, SOCK_DGRAM, 0)) < 0)	/* connect to socket */
> 	{
> 		perror("socket");
> 		exit(3);
> 	}
> 
> 	bzero((char *)&sin, (int)sizeof(sin));		/* setup address info */
> 	bcopy(the_addr, (char *)&sin.sin6_addr, sizeof(the_addr));
> 	sin.sin6_family = AF_INET6;
> 	sin.sin6_port = htons(3000);
> 							/* bind addr to sock */
> 	if(bind(sock, (struct sockaddr *)&sin, sizeof(sin)) < 0)
> 	{
> 		perror("bind");
> 		exit(errno);
> 	}
> 
> 	hops = 255;
> 	if(setsockopt(sock, IPPROTO_IPV6, IPV6_MULTICAST_HOPS, &hops, sizeof(hops)) < 0)
> 	{
> 		perror("setsockopt(IPV6_MULTICAST_HOPS)");
> 		exit(errno);
> 	}
> 
> 	ifindex = 0;
> #ifdef ORIG
> 	strcpy(ifname, "xl1");
> 	ifindex = if_nametoindex(ifname);
> 	if(ifindex == 0)
> 	{
> 		perror("if_nametoindex()");
> 		exit(errno);
> 	}
> 
> 	if(setsockopt(sock, IPPROTO_IPV6, IPV6_MULTICAST_IF, &ifindex, sizeof(ifindex)) < 0)
> 	{
> 		perror("setsockopt(IPV6_MULTICAST_IF)");
> 		exit(errno);
> 	}
> #endif
> 							/* setup group info */
> 	bcopy(the_addr, (char *)&mreq.ipv6mr_multiaddr, sizeof(the_addr));
> 	mreq.ipv6mr_interface = ifindex;		/* and I/F index */
> 
> 							/* join group */
> 	if(setsockopt(sock, IPPROTO_IPV6, IPV6_JOIN_GROUP, (char *)&mreq, sizeof(mreq)) < 0)
> 	{
> 		perror("setsockopt(IPV6_JOIN_GROUP)");
> 		exit(21);
> 	}
> 
> 	start_sender(sock, &sin);
> 	start_listener(sock);
> 
> 	while(wait((int *)0) != -1); /* wait for all children to die */
> 
> 	return(0);
> }
> 
> void start_sender(int sock, struct sockaddr_in6 *sin)
> {
> 	char bitbucket[2000];
> 	pid_t pid;
> 
> 	pid = fork();
> 	switch(pid)
> 	{
> 		case 0:					/* child */
> 			while(1)
> 			{				/* TX mcast PDU */
> 				strcpy(bitbucket, "How now brown cow?");
> 
> 				if(sendto(sock, bitbucket, strlen(bitbucket)+1, 0, (struct sockaddr *)sin, sizeof(*sin)) < 0)
> 				{
> 					perror("sendto(sender)");
> 					exit(23);
> 				}
> 				sleep(10);
> 			}
> 			break;
> 
> 		case -1:				/* parent fork failed */
> 			 printf("fork(sender): failed\n");
> 			 fflush(stdout);
> 			 break;
> 
> 		default: 				/* parent fork passed */
> 			 printf("sender PID = %d\n", (int)pid);
> 			 fflush(stdout);
> 			 break;
> 	}
> }
> 
> void start_listener(int sock)
> {
> 	pid_t pid;
> 	unsigned int fromlen;
> 	struct sockaddr_in6 from;
> 	char bitbucket[2000], addrstr[INET6_ADDRSTRLEN];
> 
> 	pid = fork();
> 	switch(pid)
> 	{
> 		case 0:					/* child */
> 			while(1)
> 			{
> 				bitbucket[0] = '\0';
> 				fromlen = sizeof(from);
> 				if(recvfrom(sock, bitbucket, sizeof(bitbucket),
> 					    0, (struct sockaddr *)&from,
> 					    &fromlen) < 0)
> 				{
> 					perror("listener: recvfrom()");
> 					exit(21);
> 				}
> 
> 				inet_ntop(AF_INET6, &from.sin6_addr, addrstr,
> 					  sizeof(addrstr));
> 				printf("< %s : \"%s\"\n", addrstr, bitbucket);
> 				fflush(stdout);
> 			}
> 			break;
> 
> 		case -1:				/* parent fork failed */
> 			 printf("fork(listerner): failed\n");
> 			 fflush(stdout);
> 			 break;
> 
> 		default: 				/* parent fork passed */
> 			 printf("listener PID = %d\n", (int)pid);
> 			 fflush(stdout);
> 			 break;
> 	}
> }
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> 
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