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Date:      Wed, 24 Mar 1999 14:12:37 -0700
From:      Wes Peters <wes@softweyr.com>
To:        Petri Helenius <pete@sms.fi>
Cc:        Bill Fumerola <billf@chc-chimes.com>, Peter Brezny <peter@cyber1.net>, freebsd-net@FreeBSD.ORG
Subject:   Re: switch vs bridge (fwd)
Message-ID:  <36F95545.6B1F40C0@softweyr.com>
References:  <Pine.HPP.3.96.990324150941.17143D-100000@hp9000.chc-chimes.com> <36F95064.670D0DA1@sms.fi>

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Petri Helenius wrote:
> 
> Bill Fumerola wrote:
> >
> > On Wed, 24 Mar 1999, Petri Helenius wrote:
> >
> > > > A switch replicates packets based on their Ethernet destination.
> > > >
> > > And how exactly would you describe a bridge then?
> >
> > Anything I say is going to be able to be picked apart,
> >
> > but a bridge replicates any data it sees for its destination network and
> > just shoves it over.
> >
> > A switch makes an intelligent port-by-port decision.
> >
> 99% of ethernet bridges out there have a forwarding table as the switches
> have which are multiport bridges. It's a completely different ballgame for
> token ring though.
> 
> There is no concept of "network" in ethernet so you cannot do any actions
> based on the addressing other than learn where all the sources are. This
> process
> is equally the same for bridges and switches. (since they are the same)

Try these on for size:

MAC-Layer Bridge - A device used to forward data between LANs at layer two,
by automatically filtering out traffic which is local to each LAN, while
forwarding on traffic which is not local to each LAN.  All broadcasts
and multicasts, as well as all traffic with a destination address which 
has not been learned by the bridge, is forwarded.

MAC-Layer Switching - LAN data transferred through a network based on the
source and destination address contained in the MAC header of the frame.
Essentially the same as bridging, but almost always employing dedicated
hardware to perform the switching.

In other words, there isn't a whole lot of difference unless you step
up to layer three switches.

These definitions taken from "The Switching Book II", from Xylan Corp.
Download a PDF version or order your own free printed copy at:

	http://www.xylan.com/library/switchbook/index.html

While you're there, poke around and buy something.  ;^)

-- 
             Where am I, and what am I doing in this handbasket?

Wes Peters                                                     +1.801.915.2061
Softweyr LLC                                                  wes@softweyr.com


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