Date: Wed, 22 Mar 2000 09:04:07 -0800 From: "Sam Leffler" <sam@errno.com> To: <freebsd-net@FreeBSD.ORG>, "C. Stephen Gunn" <csg@waterspout.com> Subject: Re: Trimming ether_header before ether_input() Message-ID: <005301bf9420$a53ebdc0$0132a8c0@MELANGE> References: <200003220239.VAA01543@dustdevil.waterspout.com>
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----- Original Message -----
From: "C. Stephen Gunn" <csg@waterspout.com>
To: <freebsd-net@FreeBSD.ORG>
Sent: Tuesday, March 21, 2000 6:39 PM
Subject: Trimming ether_header before ether_input()
> In my wanderings through the FreeBSD networking code, I've noticed
> something peculiar in all ethernet drivers. Is there a historical
> reason that the ethernet header is trimmed from the mbuf chain
> before its passed to ether_input()?
>
> I can only assume that (at one time) there were ethernet devices
> (back in the IMP days) that handed you the link header and the
> payload in separate buffers.
>
When all this code was written there was a link layer encapsulation called a
trailer protocol that placed the Ethernet header at the end of the packet.
I think it's described in the "real BSD book" (the 4.2 one, not a later one
:-)); if not there is an RFC that describes it.
Sam
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