Date: Wed, 1 Jan 2014 23:13:28 -0800 From: John-Mark Gurney <jmg@funkthat.com> To: Peter Jeremy <peter@rulingia.com> Cc: freebsd-net@freebsd.org Subject: Re: IPv4 Multicast MAC Address issues Message-ID: <20140102071328.GW99167@funkthat.com> In-Reply-To: <20140102064356.GL87348@server.rulingia.com> References: <20140101085721.GA34334@server.rulingia.com> <20140101200303.GS99167@funkthat.com> <20140102064356.GL87348@server.rulingia.com>
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Peter Jeremy wrote this message on Thu, Jan 02, 2014 at 17:43 +1100:
> On 2014-Jan-01 12:03:04 -0800, John-Mark Gurney <jmg@funkthat.com> wrote:
> >Peter Jeremy wrote this message on Wed, Jan 01, 2014 at 19:57 +1100:
> >> I'm trying to use multicast on my home network for the first time and
> >> have found an apparent anomoly in the destination MAC address.
> ...
> >> FreeBSD shows that as the multicast MAC filter. Unfortunately, it
> >> seems that (at least on FreeBSD-10), the destination MAC address
> >> uses the low 23 bits of the IP address of my default route.
>
> >This is probably a bug, and I have confirmed this on:
> >FreeBSD carbon.funkthat.com 11.0-CURRENT FreeBSD 11.0-CURRENT #4 r256870:258399M: Wed Nov 20 12:33:22 PST 2013 jmg@carbon.funkthat.com:/usr/src/sys/amd64/compile/lockprof amd64
>
> Thanks. I've since checked 9.2/amd64 and it's OK there, so this is a
> regression. I've raised kern/185395.
I've done a quick look at the code and I don't see anything that changed
that is odd, but I did notice that ETHER_MAP_IP_MULTICAST in if_ether.h
doesn't put parens around ipaddr, but it's only use in if_ether.c looks
safe. The one change around this code is the addition of const in the
macro, but I don't think that could cause the issue...
Hmmm... looking at the comments for arpresolve, it says dst is the next
hop which would be the gateway, and not the multicast address, so that
could be it, but I don't know the code well enough to figure out why
dst isn't the multicast address...
--
John-Mark Gurney Voice: +1 415 225 5579
"All that I will do, has been done, All that I have, has not."
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