Re: Is it possible to bridge three NIC on a Windows 2000 Server
From: Herb Martin (news_at_LearnQuick.com)
Date: 02/17/05
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Date: Thu, 17 Feb 2005 11:33:05 -0600
"Phillip Windell" <@.> wrote in message
news:Orcv6AQFFHA.2600@TK2MSFTNGP09.phx.gbl...
> "Herb Martin" <news@LearnQuick.com> wrote in message
> news:eIXnojFFFHA.1392@tk2msftngp13.phx.gbl...
> > > To me, Switch and Bridge are synonymous with
> > > Switches simply having more ports (multi-port-bridge).
> >
> > You have been misinformed. They are distinct device
> > type, possibly with some overlapping features.
>
> We'll have to agree to disagree. I have not been misinformed. I am basing
it
> right from Cisco's material used to train CCNA's.
Then you are wrong (to disagree) as the material you are using
is either grossly oversimplified (to the point of being wrong)
or you have misunderstood it.
> MS's materials for the
> "Networking Essentials" exam (or whatever they call it now agrees with
> Cisco).
Then that source is wrong too.
Switches electronically hook multiple segments or legs
together (briefly) -- the analogy is like a switch board.
Someone having a naive understanding of the way SOME
switches work might have written something that ASSUMES
(incorrectly) that all switches are using bridging methods
to make the decision when and what to connect.
They could be referring specifically to a bridge type switch
(either explicitly or by context) and you might have missed
that distinction.
Probably the source (if it is useful at all) is making some
general and introductory comments or is just purely written
rather than outright wrong but the result is the same if it
caused you to misunderstand.
Swithes are divided into two major classes:
1) Layer-2 switches (Bridge type switches)
2) Router-Switches (Layer-3 switches)
(I used the most common name first here)
They operate different. One uses Router methods (routing tables
and Protocol specific information) and the other uses bridging
methods (MAC address, clien OS and protocol transparency,
forward all broadcasts by default).
There are also today many hybrid devices able to do both,
or even to configure some ports in a bridged set, while
router to other (sets) of ports. Usually called a VLAN
switch since each CUSTOM broacast domain is called a
VLAN.
> The early ones only had two ports and were called bridges, later as
> they evolved they were given more ports and were then called "multi-port
> bridges",..then later someone got the bright idea of calling them
"Switches"
No, they they "got the idea" because these SWITCH (electically
connect the two endpoints) rather than store and forward as does
a pure bridge.
> due to the Layer2 Packet Switching ability which was the heart of what
> Bridges do.
No. Pure bridges do NOT "switch".
They store (briefly in memory buffer) and forward.
> That is the name that "stuck" and is what they are known by
> today. The term "bridging" somewhat faded away over time and was relegated
> mostly to routing devices
Routers are entirely different type of device from a
bridge.
> on WAN links that ran in "bridging mode" because
> both ends of the WAN link were the same subnet.
That part is correct and thus they are NOT acting as
routers.
(Actually these are devices originally called "half bridges"
or "wan bridges" since half of the bridge is on each side
of the WAN.)
> But the term has been
> resurrected again with the latest MS OS's with the Nic Bridging that
simply
> makes the computer function as a Layer2 switching device (aka
> bridge/switch).
No. It is only a Bridge and DEFINITELY not a Switch
in correct network terminology.
There IS NOT electrical connection from port A to B
at any time -- it is just a computer with two NICs.
A switch would actually "switch in a direct connection
through it's backplane."
But the REALLY critical distinction you are missing is
between a Router and a Bridge (ignoring whether these
are embedded in the more modern electronics of a
switch.)
> If it only has two Nics it would be a parallel to the old
> two-port bridges, if it has more Nics, with all bridged together,
They operate the same whether there are 2 or 16 NICs.
You are making another false distinction.
> then it
> begins operate the same as a Switch,...which is kind of pointless to me
> since you can go out and buy a cheap switch for $50 that does the same
> thing.
You are probably talking about one of the misnamed (this time
by the product advertisers) 10/100 'switches'.
This may be another part of your misunderstanding but it is
largely due to ADVERTISING because this is NOT a switch
in the network engineering sense EITHER.
These devices are really a 10 Mbps multiport repeater
(i.e., SIMPLE hub) BRIDGED to a 100 Mbps multiport
repeater -- to hubs with a bridge in between that have all
been integrated into the same box.
The only "switching" that takes place is that when a 10 Mbps
station plugs in it is STATICALLY switched to the 10 Mbps
side (or hub.)
A dynamic network switch as we have been discussing above
does something more complicated on each packet.
> > Switches are not even always based on bridges, but may
> > be switch-routers (layer 3) or some hybrid of a bridge
> > and router switch.
>
> The Layer3 Switch is a hybrid "Johnny-come-lately". They do not "define"
> what Switches do, they are unique to themselves and do both the job of a
> Router and a Switch.
No, again you have misunderstood: They do what switches
do -- but they use ROUTERS method to decice when and what
to swich.
This is your basic misunderstanding (if you care to fix
it rather than just argue) when you miss the KEY distinctions
between BRIDGE and ROUTER.
> We paid about $10,000.00 for ours due to additional
> add-ons and modules.
Irrelevant. Router and Bridge differences are the key to
your understanding this subject.
> > If you wish to fully understand you need to start with
> > CLASSICAL (simple) bridges and routers, learn their
> > KEY points and then apply this knowledge to understanding
> > modern hybrid/complex switches.
>
> I didn't just start yesterday. I've "been there, done that". I'm trying
to
> explain those things, not learn them as if I didn't know what they were.
And you have based it on misunderstanding or misinformation.
Your choice.
> > > You can have two physcial segments connected with a Switch (aka
Bridge)
>
> If a Switch or Bridge separates thm, then it isn't two segments but just
> one. Without the router there is no separation.
Exactly but it was TWO before you hooked in the bridge.
(whether it is a switch or not)
> > > after all, it is the router that creates the broadcast domain,
> >
> > No. Routers generally DO not join broadcast domains like
> > bridges do.
>
> Umm,...that is what I've been saying.
So if you join to broadcast domains with a Bridge,
and then try to JOIN them again with another bridge
you CAUSE broadcast loops.
That was the original point you misunderstood.
[I see you snipped out the thought experiment so here it is
again]
No, the physical wiring sets up the 'units' of the broadcast
domain and any bridges may join multiple physical segments
into a larger broadcast domain.
Do NOT hook a bridge TWICE to the same broadcast domain.
This is not the same as saying you hook a bridge to two
broadcast domains to CONVERT them into one broadcast
domain.
Do the following though experiment: Take a pair of bridges
and hook them to the same physical segment then to each other
on another segment...
What happens when a broadcast occurs on one of the segments?
What does each bridge do with broadcasts?
Does the other bridge 'see' the propagation to the other shared
segment? What does it do with that?
(And the first bridge, what does it do when it hears the other
bridge propagate the broadcast?)
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