Date: Mon, 29 Apr 2024 10:52:28 -0700 (PDT) From: "Rodney W. Grimes" <freebsd-rwg@gndrsh.dnsmgr.net> To: Dirk-Willem van Gulik <dirkx@webweaving.org> Cc: "Rodney W. Grimes" <freebsd-rwg@gndrsh.dnsmgr.net>, FreeBSD Hackers <freebsd-hackers@FreeBSD.org> Subject: Re: Multicast & Tunnel devices Message-ID: <202404291752.43THqS5l074359@gndrsh.dnsmgr.net> In-Reply-To: <2C4BC70A-750C-4E0F-B400-351CBBD6374B@webweaving.org>
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>
> > On 29 Apr 2024, at 03:09, Rodney W. Grimes <freebsd-rwg@gndrsh.dnsmgr.net> wrote:
> >
> >> Would anyone know if there is something special with tunnel devices and multicast ?
> >>
> >> I?ve got some code that happily processes multicast packets on a normal interface; but appears not to do this on a tunnel interface. Tun0 shows multicast enabled:
> >>
> >> tun0: flags=8043<UP,BROADCAST,RUNNING,MULTICAST> metric 0 mtu 1500
> >>
> >> Tcpdump on that interface gives the expected thing (here with mDNS):
> >>
> >> tcpdump -n -i tun0 port 5353
> >> listening on tun0, link-type NULL (BSD loopback), capture size 262144 bytes
> >> 19:26:03.976259 IP 10.31.0.6.5353 > 224.0.0.251.5353: 0 PTR (QM)? _raop._tcp.local. (34)
> >>
> >> And code, with a simple IP_ADD_MEMBERSHIP of the MC group on the IP of the local interface below works on a normal interface (e.g. igb0/10.0.0.1/24).
> >>
> >> ./listener 10.0.0.1 224.0.0.251 5353
> >
> > Is 10.0.0.1 the IP address of tun0, or is it the address of some other interface?
> > I suspect that the IP address of the tun0 interface is 10.31.0.6 from your tcpdump above.
>
> That is correct 10.0.0.1/8. 10.31.0.6 is another machine at the other end of the tunnel broadcasting.
>
> > IIRC you have to join multicast group on all interfaces you expect to receive mustcast packets on.
> >
> >> Received packet, len=128
> >> etc
> >>
> >> But yields no output if ran against above tun0 interface (while tcpdump on same is fine). Does that ring a bell with anyone ?
> >>
> >> Dw
> >>
> >>
> >> int main(int argc, char *argv[])
> >> {
> >> struct sockaddr_in addr;
> >> struct ip_mreq mreq;
> >>
> >> // skip error trapping command line arguments
> >>
> >> char* ip = argv[1];
> >> char* group = argv[2];
> >> int port = atoi(argv[3]); // 0 if error, which is an invalid port
> >>
> >> memset(&addr, 0, sizeof(addr));
> >> addr.sin_family = AF_INET;
> >> addr.sin_addr.s_addr = htonl(INADDR_ANY);
> >> addr.sin_port = htons(port);
> >>
> >> mreq.imr_interface.s_addr = inet_addr(ip);
> >> mreq.imr_multiaddr.s_addr = inet_addr(group);
> >>
> >> // skip error trapping on inet_addr
> >>
> >> int fd = socket(AF_INET, SOCK_DGRAM, 0);
> >> // skip error trapping socket
> >>
> >> if (bind(fd, (struct sockaddr*) &addr, sizeof(addr)) < 0) {
> >> // skip error trapping
> >>
> >> if (setsockopt(fd, IPPROTO_IP, IP_ADD_MEMBERSHIP, (char*) &mreq, sizeof(mreq)) < 0 ){
> >> // skip error trapping argumetns
> >>
> >> while (1) {
> >> ..
> >> int nbytes = recvfrom(fd,msgbuf,MSGBUFSIZE,0,(struct sockaddr *) &addr,&addrlen);
> >> if (nbytes < 0) {
> >> perror("recvfrom");
> >> return 1;
> >> }
> >> printf(?Received packet, len=%d\n", nbytes);
> >> }
> >>
>
--
Rod Grimes rgrimes@freebsd.org
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