[9fans] Multicast

[9fans] Multicast

[Adriano Verardo]

Hi, all
I need to define a unicast group to implement an application on a set of
cooperative CPUs.
The ip(3) man page is (for me) not clear enough and searching  for
"multicast" etc in /sys/src/*/*/...
doesn't give any useful result. The same looking in sources/contrib

Where can I find an example on how to exchange multicast packets among
CPUs wired to the
same ethernet switch ?

Thanks in advance
adriano

Re: [9fans] Multicast

[erik quanstrom]

On Mon Dec 24 14:12:52 EST 2012, adriano.verardo@mail.com wrote:
> Hi, all I need to define a unicast group to implement an application
> on a set of cooperative CPUs.  The ip(3) man page is (for me) not
> clear enough and searching for "multicast" etc in /sys/src/*/*/...
> doesn't give any useful result.  The same looking in sources/contrib
>
> Where can I find an example on how to exchange multicast packets among
> CPUs wired to the same ethernet switch ?

this isn't something i've ever done, but having fiddled quite a bit in the
network stack, and with drivers, so...

in any case, you will need to add muticast addresses to the hw interfaces.
assuming ethernet, ether(3) has the correct information.  if you want to
associate that mc address with a name, you'll need to edit your ndb files
to have sys=name ether=mcaddress.

if the protocol you're using is ip, you'll need to also need to bind in an
ip mc address.  using ipconfig(8) is generally easiest.  i don't see any reason
why you can't add it in like a non-mc address.  you may also wish
to add a dom= line to your ndb file.

- erik

Re: [9fans] multicast

[Jeff Sickel]

Steve,

Did you ever figure out how to setup addmulti?

-jas

> On Oct 6, 2014, at 10:41 AM, Steve Simon <steve@quintile.net> wrote:
>
> I am trying to listen to multicast DNS packets
> but when I try to configure the IP interface it fails,
> what am I missing?
>
> I do this (multicast with promiscuous)
>
> 	snprint(addr, sizeof(addr), "%s/udp!*!*", Netdir);
> 	if((cfd = announce(addr, dir)) < 0)
> 		sysfatal("%s cannot announce, %r\n", addr);
> 	if(fprint(cfd, "addmulti 224.0.0.251") < 0)
> 		sysfatal("add multicast addr 224.0.0.251 failed, %r");
>
> and it dies with 'addmulti for a non multicast address'
>
> which is caused by this failing:
>
> /sys/src/9/ip/ipifc.c
>
> 	int
> 	ipismulticast(uchar *ip)
> 	{
> 		if(isv4(ip)){
> 			if(ip[IPv4off] >= 0xe0 && ip[IPv4off] < 0xf0)
> 				return V4;
> 		}
> 		else if(ip[0] == 0xff)
> 			return V6;
> 		return 0;
> 	}
>
> But 0xe0 is 224 so it should not fail.
>
> I'am very confused.
>
> -Steve
>

[9fans] multicast

[Steve Simon]

I am trying to listen to multicast DNS packets
but when I try to configure the IP interface it fails,
what am I missing?

I do this (multicast with promiscuous)

	snprint(addr, sizeof(addr), "%s/udp!*!*", Netdir);
	if((cfd = announce(addr, dir)) < 0)
		sysfatal("%s cannot announce, %r\n", addr);
	if(fprint(cfd, "addmulti 224.0.0.251") < 0)
		sysfatal("add multicast addr 224.0.0.251 failed, %r");

and it dies with 'addmulti for a non multicast address'

which is caused by this failing:

/sys/src/9/ip/ipifc.c

	int
	ipismulticast(uchar *ip)
	{
		if(isv4(ip)){
			if(ip[IPv4off] >= 0xe0 && ip[IPv4off] < 0xf0)
				return V4;
		}
		else if(ip[0] == 0xff)
			return V6;
		return 0;
	}

But 0xe0 is 224 so it should not fail.

I'am very confused.

-Steve