Date: Thu, 10 Nov 2011 13:40:05 -0600 From: "David DeSimone" <fox@verio.net> To: <freebsd-net@freebsd.org> Subject: Re: FreeBSD 9 and ARP multicast source address error messages Message-ID: <20111110194004.GB7844@verio.net> In-Reply-To: <6A964045-2ADF-42EC-8AC4-00179FDBE4D9@msu.edu> References: <96A5211A-398B-4773-8C6A-2D772D241CF0@msu.edu> <20111110065135.GS71907@FreeBSD.org> <6A964045-2ADF-42EC-8AC4-00179FDBE4D9@msu.edu>
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Alexander Wittig <wittigal@msu.edu> wrote:
>
> Nov 10 12:25:45 bt kernel: in_arp: 03:bf:23:09:44:e4 is multicast
> Nov 10 12:25:45 bt kernel: in_arp: 03:bf:23:09:44:87 is multicast
> [...]
>
> I'm not an expert on networking, but is this condition of ignoring
> such an ARP packet really a noteworthy event? I.e. is this something
> that should not occur in "normal" operation according to the ARP
> specifications? If this is mostly for kernel developers, maybe it
> should only be enabled in debug kernel builds?
I found this tread enlightening on the subject:
http://fixunix.com/tcp-ip/66685-arp-reply-containing-multicast-mac-ok.html
In particular the reference to RFC 1812 which states:
A router MUST not believe any ARP reply that claims that the Link
Layer address of another host or router is a broadcast or multicast
address.
This requirement is the reason why multicast ARP replies are
problematic, and why Microsoft's NLB implementation often causes
heartburn within the network.
--
David DeSimone == Network Admin == fox@verio.net
"I don't like spinach, and I'm glad I don't, because if I
liked it I'd eat it, and I just hate it." -- Clarence Darrow
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