Date: Thu, 6 Jul 2000 17:37:29 +0200 (CEST) From: Luigi Rizzo <luigi@info.iet.unipi.it> To: tim@iafrica.com.na Cc: David Gilbert <dgilbert@velocet.ca>, Kevin Oberman <oberman@es.net>, "Louis A. Mamakos" <louie@TransSys.COM>, Joerg Micheel <joerg@cs.waikato.ac.nz>, freebsd-stable@FreeBSD.ORG Subject: Re: Ethernet MTUs > 1500? Message-ID: <200007061537.RAA85384@info.iet.unipi.it> In-Reply-To: <39647CE2.C1D11DD5@polytechnic.edu.na> from Tim Priebe at "Jul 6, 2000 01:34:42 pm"
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> An Ethernet frame with vlan tagging does _not_ have an extra header etc, however you see it, it's the original bits plus some extra bits! > When a tagged packet must be sent out ports that are not tagged for that > vlan, the reverse process occures. The tagged header is removed, and > replaced with a new one. Obviously new CRC values are generated each i am not sure about this one: my understandinbg reading the spec (18months ago) was that tagged packets only go out on trunk interfaces (unmodified) or on interfaces tagged for that VLAN (this time they are untagged). > If the switch does some thing strange, like using different vlan tag > values for the same vlan on different interfaces, then it would have to > change the tag value, and recalculate the CRC. This is too complex a Why are you so worried by the CRC, which is compuited on the fly by the interface as bits are sent on the wire ? > > I do know how my FreeBSD-based > > vlan bridge behaves -- it does multiple encaps, but then if a > > packet becomes too large it is silently dropped by the interface. > > If it encapsulates the the original frame including the original headers > in a new ethernet frame, then it is doing it wrong, and can not be > expected to interoperate with a bridge that does it right. Your frames sorry i used the wrong terminology -- i said "encapsulate/decapsulate" but meant "tag/untag" -- and it did interoperate with a real VLAN bridge (802.1Q) cheers luigi -----------------------------------+------------------------------------- Luigi RIZZO, luigi@iet.unipi.it . Dip. di Ing. dell'Informazione http://www.iet.unipi.it/~luigi/ . Universita` di Pisa TEL/FAX: +39-050-568.533/522 . via Diotisalvi 2, 56126 PISA (Italy) Mobile +39-347-0373137 -----------------------------------+------------------------------------- To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-stable" in the body of the message
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