From owner-freebsd-stable Thu Jul 6 8:29:50 2000 Delivered-To: freebsd-stable@freebsd.org Received: from info.iet.unipi.it (info.iet.unipi.it [131.114.9.184]) by hub.freebsd.org (Postfix) with ESMTP id 47AF437BAAA for ; Thu, 6 Jul 2000 08:29:27 -0700 (PDT) (envelope-from luigi@info.iet.unipi.it) Received: (from luigi@localhost) by info.iet.unipi.it (8.9.3/8.9.3) id RAA85343; Thu, 6 Jul 2000 17:29:14 +0200 (CEST) (envelope-from luigi) From: Luigi Rizzo Message-Id: <200007061529.RAA85343@info.iet.unipi.it> Subject: Re: Ethernet MTUs > 1500? In-Reply-To: <14692.32743.852986.408436@trooper.velocet.net> from David Gilbert at "Jul 6, 2000 08:47:35 am" To: David Gilbert Date: Thu, 6 Jul 2000 17:29:14 +0200 (CEST) Cc: tim@iafrica.com.na, Kevin Oberman , "Louis A. Mamakos" , Joerg Micheel , freebsd-stable@FreeBSD.ORG X-Mailer: ELM [version 2.4ME+ PL61 (25)] MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-freebsd-stable@FreeBSD.ORG Precedence: bulk X-Loop: FreeBSD.ORG > Naw... that's not how you'd configure it. Lets say we have this: > > ---------- ---------- ---------- --------- > | A |--------| B |--------| C |---------| D | > ---------- ---------- ---------- --------- > > Now... if a packet leaves A on vlan 57, it will arrive at B marked > with vlan 57. If the BC link is the "same" trunk, the packet might > continue on vlan 57. Now if the CD link is a different "trunk" (and > this is just an organizational issue), then the packet might be > rewritten to have vlan 225 on it --- and would make that leg of the > journey with vlan 225. hmm... my understanding was (but i might be wrong) that _normally_ end hosts do not tag packets, the tag insertion/removal (this is what i meant by encapsulation/decapsulation in my previous email) is done by the VLAN bridge when such packets go through a trunk interface (i.e. the link connected to that interface supports traffic for multiple independent VLANs). My point is that you don't know what happens to the traffic on that link -- your network admin could decide to further aggregate such traffic by forwarding it into a "normal" port of another VLAN bridge, which then does the tagging again. Agreed, this is not how you'd configure it, but as you say > ........................ The possibilites simply explode ... not the > In short, vlan tags are not like GRE (which might be the confusion) > ... they are simply part of the ethernet header. not fully sure about that. How could you possibly prevent a frame from being untagged multiple times if the frame has an appropriate bit pattern ? 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