Date: Tue, 28 Aug 2001 10:35:36 -0700 From: Brooks Davis <brooks@one-eyed-alien.net> To: Garrett Wollman <wollman@khavrinen.lcs.mit.edu> Cc: Mike Tancsa <mike@sentex.net>, freebsd-net@FreeBSD.ORG Subject: Re: Runt frames = broken VLAN ? Message-ID: <20010828103536.D10481@Odin.AC.HMC.Edu> In-Reply-To: <200108281654.f7SGsIF38299@khavrinen.lcs.mit.edu>; from wollman@khavrinen.lcs.mit.edu on Tue, Aug 28, 2001 at 12:54:18PM -0400 References: <5.1.0.14.0.20010828010515.0221d380@192.168.0.12> <200108281654.f7SGsIF38299@khavrinen.lcs.mit.edu>
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[-- Attachment #1 --] On Tue, Aug 28, 2001 at 12:54:18PM -0400, Garrett Wollman wrote: > <<On Tue, 28 Aug 2001 01:05:32 -0400, Mike Tancsa <mike@sentex.net> said: > > > Can anyone tell me why the VLAN code might be causing my switches (ciscos) > > to see a lot of runt frames when the interface is in 802.1q trunking mode ? > > It's possible that the Cisco is (bogusly, IMHO) trying to enforce the > Ethernet minimum frame length on the *de*capsulated frames. If you > send a frame that's less than 60 octets long, it gets encapsulated > (adding another four octets) and then padded by the interface up to 64 > octets. After the encapsulation is removed by the receiver, the frame > appears to only be 60 octets long. > > I'd call it a Cisco bug. The minimum frame length in Ethernet arises > from the electrical parameters of the original CSMA/CD Ethernet > design; what matters is the number of clocks the transmitter is > active, not the length of the payload. But doesn't the switch have to assume that the VLAN will be attached to some non-trunked ports, in which case the packets must be an appropriate length. From a switch vendor's perspective the case of a VLAN with no non-trunked ports is going to be a bizzare edge case. -- Brooks -- Any statement of the form "X is the one, true Y" is FALSE. PGP fingerprint 655D 519C 26A7 82E7 2529 9BF0 5D8E 8BE9 F238 1AD4 [-- Attachment #2 --] -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.0.6 (GNU/Linux) Comment: For info see http://www.gnupg.org iD8DBQE7i9ZnXY6L6fI4GtQRAtosAJ9ESjVjJL8JijDjcDP6n1aCxcY7ogCgs11J EJQXU/gOTI8noHzpxFiUCmo= =7/y+ -----END PGP SIGNATURE-----
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