Date: Mon, 29 Apr 2024 16:36:20 +0200 From: Dirk-Willem van Gulik <dirkx@webweaving.org> To: "Rodney W. Grimes" <freebsd-rwg@gndrsh.dnsmgr.net> Cc: FreeBSD Hackers <freebsd-hackers@FreeBSD.org> Subject: Re: Multicast & Tunnel devices Message-ID: <2C4BC70A-750C-4E0F-B400-351CBBD6374B@webweaving.org> In-Reply-To: <202404290109.43T19HKw071603@gndrsh.dnsmgr.net> References: <202404290109.43T19HKw071603@gndrsh.dnsmgr.net>
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> On 29 Apr 2024, at 03:09, Rodney W. Grimes =
<freebsd-rwg@gndrsh.dnsmgr.net> wrote:
>=20
>> Would anyone know if there is something special with tunnel devices =
and multicast ?=20
>>=20
>> 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:
>> =09
>> tun0: flags=3D8043<UP,BROADCAST,RUNNING,MULTICAST> metric 0 mtu =
1500
>>=20
>> Tcpdump on that interface gives the expected thing (here with mDNS):
>>=20
>> 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)
>>=20
>> 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).=20
>>=20
>> ./listener 10.0.0.1 224.0.0.251 5353
>=20
> 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.
>=20
>> Received packet, len=3D128
>> etc
>>=20
>> But yields no output if ran against above tun0 interface (while =
tcpdump on same is fine). Does that ring a bell with anyone ?
>>=20
>> Dw
>>=20
>>=20
>> int main(int argc, char *argv[])
>> {
>> struct sockaddr_in addr;
>> struct ip_mreq mreq;
>>=20
>> // skip error trapping command line arguments
>>=20
>> char* ip =3D argv[1];=20
>> char* group =3D argv[2];=20
>> int port =3D atoi(argv[3]); // 0 if error, which is an invalid =
port
>>=20
>> memset(&addr, 0, sizeof(addr));
>> addr.sin_family =3D AF_INET;
>> addr.sin_addr.s_addr =3D htonl(INADDR_ANY);
>> addr.sin_port =3D htons(port);
>>=20
>> mreq.imr_interface.s_addr =3D inet_addr(ip);=20
>> mreq.imr_multiaddr.s_addr =3D inet_addr(group);
>>=20
>> // skip error trapping on inet_addr
>>=20
>> int fd =3D socket(AF_INET, SOCK_DGRAM, 0);
>> // skip error trapping socket
>>=20
>> if (bind(fd, (struct sockaddr*) &addr, sizeof(addr)) < 0) {
>> // skip error trapping
>>=20
>> if (setsockopt(fd, IPPROTO_IP, IP_ADD_MEMBERSHIP, (char*) &mreq, =
sizeof(mreq)) < 0 ){
>> // skip error trapping argumetns
>>=20
>> while (1) {
>> ..
>> int nbytes =3D recvfrom(fd,msgbuf,MSGBUFSIZE,0,(struct =
sockaddr *) &addr,&addrlen);
>> if (nbytes < 0) {
>> perror("recvfrom");
>> return 1;
>> }
>> printf(?Received packet, len=3D%d\n", nbytes);
>> }
>>=20
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<html><head><meta http-equiv=3D"content-type" content=3D"text/html; =
charset=3Dus-ascii"></head><body style=3D"overflow-wrap: break-word; =
-webkit-nbsp-mode: space; line-break: after-white-space;"><br =
id=3D"lineBreakAtBeginningOfMessage"><div><br><blockquote =
type=3D"cite"><div>On 29 Apr 2024, at 03:09, Rodney W. Grimes =
<freebsd-rwg@gndrsh.dnsmgr.net> wrote:</div><br =
class=3D"Apple-interchange-newline"><div><meta =
charset=3D"UTF-8"><blockquote type=3D"cite" style=3D"font-family: =
Helvetica; font-size: 12px; font-style: normal; font-variant-caps: =
normal; font-weight: 400; letter-spacing: normal; orphans: auto; =
text-align: start; text-indent: 0px; text-transform: none; white-space: =
normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; =
text-decoration: none;">Would anyone know if there is something special =
with tunnel devices and multicast ?<span =
class=3D"Apple-converted-space"> </span><br><br>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:<br><span class=3D"Apple-tab-span" style=3D"white-space: pre;"> =
</span><br><span class=3D"Apple-tab-span" style=3D"white-space: pre;"> =
</span>tun0: flags=3D8043<UP,BROADCAST,RUNNING,MULTICAST> metric 0 =
mtu 1500<br><br>Tcpdump on that interface gives the expected thing (here =
with mDNS):<br><br><span class=3D"Apple-tab-span" style=3D"white-space: =
pre;"> </span>tcpdump -n -i tun0 port 5353<br><span =
class=3D"Apple-tab-span" style=3D"white-space: pre;"> </span>listening =
on tun0, link-type NULL (BSD loopback), capture size 262144 =
bytes<br><span class=3D"Apple-tab-span" style=3D"white-space: pre;"> =
</span>19:26:03.976259 IP 10.31.0.6.5353 > 224.0.0.251.5353: 0 PTR =
(QM)? _raop._tcp.local. (34)<br><br>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).<span =
class=3D"Apple-converted-space"> </span><br><br><span =
class=3D"Apple-tab-span" style=3D"white-space: pre;"> =
</span>./listener 10.0.0.1 224.0.0.251 5353<br></blockquote><br =
style=3D"caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: =
12px; font-style: normal; font-variant-caps: normal; font-weight: 400; =
letter-spacing: normal; text-align: start; text-indent: 0px; =
text-transform: none; white-space: normal; word-spacing: 0px; =
-webkit-text-stroke-width: 0px; text-decoration: none;"><span =
style=3D"caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: =
12px; font-style: normal; font-variant-caps: normal; font-weight: 400; =
letter-spacing: normal; text-align: start; text-indent: 0px; =
text-transform: none; white-space: normal; word-spacing: 0px; =
-webkit-text-stroke-width: 0px; text-decoration: none; float: none; =
display: inline !important;">Is 10.0.0.1 the IP address of tun0, or is =
it the address of some other interface?</span><br style=3D"caret-color: =
rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: =
normal; font-variant-caps: normal; font-weight: 400; letter-spacing: =
normal; text-align: start; text-indent: 0px; text-transform: none; =
white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; =
text-decoration: none;"></div></blockquote><div><blockquote =
type=3D"cite">I suspect that the IP address of the tun0 interface is =
10.31.0.6 from your tcpdump above.<br></blockquote><br></div>That is =
correct 10.0.0.1/8. 10.31.0.6 is another machine at the other end of the =
tunnel broadcasting.</div><div><br></div><div><blockquote =
type=3D"cite"><div><span style=3D"caret-color: rgb(0, 0, 0); =
font-family: Helvetica; font-size: 12px; font-style: normal; =
font-variant-caps: normal; font-weight: 400; letter-spacing: normal; =
text-align: start; text-indent: 0px; text-transform: none; white-space: =
normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; =
text-decoration: none; float: none; display: inline !important;">IIRC =
you have to join multicast group on all interfaces you expect to receive =
mustcast packets on.</span><br style=3D"caret-color: rgb(0, 0, 0); =
font-family: Helvetica; font-size: 12px; font-style: normal; =
font-variant-caps: normal; font-weight: 400; letter-spacing: normal; =
text-align: start; text-indent: 0px; text-transform: none; white-space: =
normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; =
text-decoration: none;"><br style=3D"caret-color: rgb(0, 0, 0); =
font-family: Helvetica; font-size: 12px; font-style: normal; =
font-variant-caps: normal; font-weight: 400; letter-spacing: normal; =
text-align: start; text-indent: 0px; text-transform: none; white-space: =
normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; =
text-decoration: none;"><blockquote type=3D"cite" style=3D"font-family: =
Helvetica; font-size: 12px; font-style: normal; font-variant-caps: =
normal; font-weight: 400; letter-spacing: normal; orphans: auto; =
text-align: start; text-indent: 0px; text-transform: none; white-space: =
normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; =
text-decoration: none;"><span class=3D"Apple-tab-span" =
style=3D"white-space: pre;"> </span>Received packet, len=3D128<br><span=
class=3D"Apple-tab-span" style=3D"white-space: pre;"> =
</span>etc<br><br>But yields no output if ran against above tun0 =
interface (while tcpdump on same is fine). Does that ring a bell with =
anyone ?<br><br>Dw<br><br><br>int main(int argc, char =
*argv[])<br>{<br> struct sockaddr_in =
addr;<br> struct ip_mreq mreq;<br><br><span =
class=3D"Apple-tab-span" style=3D"white-space: pre;"> </span>// skip =
error trapping command line arguments<br><br> char* ip =
=3D argv[1];<span =
class=3D"Apple-converted-space"> </span><br> char* =
group =3D argv[2];<span =
class=3D"Apple-converted-space"> </span><br> int =
port =3D atoi(argv[3]); // 0 if error, which is an invalid =
port<br><br> memset(&addr, 0, =
sizeof(addr));<br> addr.sin_family =3D =
AF_INET;<br> addr.sin_addr.s_addr =3D =
htonl(INADDR_ANY);<br> addr.sin_port =3D =
htons(port);<br><br> mreq.imr_interface.s_addr =3D =
inet_addr(ip);<span =
class=3D"Apple-converted-space"> </span><br> mreq.im=
r_multiaddr.s_addr =3D inet_addr(group);<br><br><span =
class=3D"Apple-tab-span" style=3D"white-space: pre;"> </span>// skip =
error trapping on inet_addr<br><br> int fd =3D =
socket(AF_INET, SOCK_DGRAM, 0);<br><span class=3D"Apple-tab-span" =
style=3D"white-space: pre;"> </span>// skip error trapping =
socket<br><br> if (bind(fd, (struct sockaddr*) =
&addr, sizeof(addr)) < 0) {<br><span class=3D"Apple-tab-span" =
style=3D"white-space: pre;"> </span>// skip error =
trapping<br><br> if (setsockopt(fd, IPPROTO_IP, =
IP_ADD_MEMBERSHIP, (char*) &mreq, sizeof(mreq)) < 0 ){<br><span =
class=3D"Apple-tab-span" style=3D"white-space: pre;"> </span>// skip =
error trapping argumetns<br><br> while (1) {<br><span =
class=3D"Apple-tab-span" style=3D"white-space: pre;"> =
</span>..<br> int nbytes =3D =
recvfrom(fd,msgbuf,MSGBUFSIZE,0,(struct sockaddr *) =
&addr,&addrlen);<br> if =
(nbytes < 0) =
{<br> per=
ror("recvfrom");<br> =
return =
1;<br> }<br><span =
class=3D"Apple-tab-span" style=3D"white-space: pre;"> =
</span>printf(?Received packet, len=3D%d\n", =
nbytes);<br> }<br><br></blockquote></div></blockquo=
te></div><br></body></html>=
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