And don't forget Layer 1 switching (sometimes called routing)! ;-) See
http://www.techreview.com/articles/july00/fairley.htm for a well-written
article on optical switching.
Priscilla
At 12:02 PM 7/4/00, Howard C. Berkowitz wrote:
>>"Rodney Jackson" <[EMAIL PROTECTED]> wrote,
>>Guys,
>>
>>I need some help. Can someone please explain why Layer 3 Switching is
>>faster than Layer 2 Switching? It seems to me that with L3 the switch
>>would have to go up three layer instead of two. I may have whole concept
>>so please explain.
>
>
>*sigh* the reason you are confused is that layer 3 switching is
>principally a marketing rather than a technical term.
>
>Relaying packets based on layer 3 information is routing.
>Relaying frames based on layer 2 information is bridging or frame/cell
>switching.
>
>Each of these levels has two components:
> Path determination
> May contain dynamic routing protocols
> Will contain configuration information
> Stores best paths in a Routing Information Base(RIB) that is
> optimized for efficient updating
> May create a Forwarding Information Base (FIB) that is optimized for
> speed of lookup. Alternatively, the RIB and FIB may be the same.
> Forwarding
> Makes forwarding decisions based on the contents of the FIB
> When hardware assisted and making layer 3 decisions, often is called
> layer 3 switching
>
>So a layer 3 switch is really a hardware-accelerated router.
>
>A layer 2 switch is faster than a traditional bridge, under most
>circumstances, because:
>
> It has a very fast internal forwarding fabric interconnecting its ports
> It uses microsegmentation on its user ports
> It usually will have a hardware-assisted FIB containing layer 2
> information
>
>Things are getting more, not less, complex. Multiprotocol label switching
>(MPLS) or Cisco's tag switching makes forwarding decisions based on a
>label or tag, usually between the layer 2 and 3 headers.
>
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Priscilla Oppenheimer
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