Date: Fri, 20 Aug 1999 11:15:54 +0100 From: Kevin Bracey <kbracey@e-14.com> To: freebsd-net@freebsd.org Subject: RE: on dual-homed machine, how to specify outgoing interface to s end multicast packets Message-ID: <35277e3449%kbracey@kbracey.acorn.co.uk> In-Reply-To: <C35556591D34D111BB5600805F1961B910ECC111@RED-MSG-47>
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In message <C35556591D34D111BB5600805F1961B910ECC111@RED-MSG-47>
George Chung <gchung@microsoft.com> wrote:
> you're right, I can't ping the address. so how do I fix that?! :-)
>
> -----Original Message-----
> From: Mike Nowlin [mailto:mike@argos.org]
> Sent: Wednesday, August 18, 1999 10:27 PM
> To: George Chung
> Cc: 'freebsd-net@freebsd.org'
> Subject: Re: on dual-homed machine, how to specify outgoing interface to
> send multicast packets
>
>
>
> > On a dual-homed machine, there is no "network" portion of the destination
> > Class D address to make any kind of determination as to which outgoing
> > interface to use.
> >
> > So I make a call to
> >
> > setsockopt(fd, IPPROTO_IP, IP_MULTICAST_IF, &inaddr, sizeof(struct
> > in_addr));
> >
> > I confirm that this call works. Plus I doublechecked by giving it a bogus
> > inaddr, and it gave me errno 49 EADDRNOTAVAIL. However, when I try send a
> > packet to "225.0.0.1", I get errno 65 EHOSTUNREACH.
>
> First guess is that it's a routing problem... Try pinging that address --
> if you get a "route not available" (or similar message), that's probably
> it.
>
This is a known BSD bug - even if you specify an interface manually for
multicasts, you need a route set up for multicast packets :( As a side-
effect, IGMP messages won't get sent either, unless you have a multicast
route set up.
--
Kevin Bracey, Senior Software Engineer
Pace Micro Technology plc Tel: +44 (0) 1223 518566
645 Newmarket Road Fax: +44 (0) 1223 518526
Cambridge, CB5 8PB, United Kingdom WWW: http://www.acorn.co.uk/
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