Date: Fri, 1 Mar 2002 03:56:23 -0800 From: Luigi Rizzo <rizzo@icir.org> To: Bob Bishop <rb@gid.co.uk> Cc: "George V. Neville-Neil" <gnn@neville-neil.com>, Doug Ambrisko <ambrisko@ambrisko.com>, hackers@FreeBSD.ORG Subject: Re: Multicast problem with sis interface? Message-ID: <20020301035623.A32974@iguana.icir.org> In-Reply-To: <4.3.2.7.2.20020301112956.00c5b550@gid.co.uk> References: <200203010557.VAA1802420@meer.meer.net> <rb@gid.co.uk> <4.3.2.7.2.20020222165515.00c14850@gid.co.uk> <200203010557.VAA1802420@meer.meer.net> <4.3.2.7.2.20020301112956.00c5b550@gid.co.uk>
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On Fri, Mar 01, 2002 at 11:37:03AM +0000, Bob Bishop wrote:
> Hi,
>
> At 01:10 01/03/02 -0800, Luigi Rizzo wrote:
> >I do not agree with the explaination. Padding is padding, the actual
> >value is irrelevant. Plus, in the tcpdump below, the are actually
> >46 bytes of data, which together with the 14 of the MAC header and
> >the 4bytes of CRC make a perfectly legal packet.
>
> Correct, but the trailing 1's were supplied by the switch between the box
> with the sis and the box running tcpdump.
I find this hard to believe. The "sis" driver does the padding
itself, using ones for the padding. I have verified this locally.
And a switch which receives a short packet (runt packet) is
not supposed to pass it through.
> >What kind of protocol are we talking about ?
>
> Appletalk NBP, for instance.
can you try and instruments the calls in the protocol stack which
are issued to generate the packet ?
> >Which are the other drivers that "work" ?
>
> ed, vr, rl
ok, these three drivers behave as follows:
"ed" pads with whatever is left in the transmit buffer from
earlier transmissions;
"vr" pads with whatever is available in the mbuf after the actual data;
"rl" pads with zeroes (in the driver)
and of course
"sis" pads in hardware (with ones)
The beauty of diversity...
cheers
luigi
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