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Re: L3 Switching Huh???? [7:63728] posted 02/25/2003
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At 04:46 PM 2/25/2003 +0000, Robert Edmonds wrote:
>Layer 3 switching combines the best of switching and routing in one
>platform.  The main advantage here is speed.  The way it works is, in a
>switch you have some kind of layer 3 routing engine (aka route processor, or
>RP).  For example, the MSFC2 (Multilayer Switch Feature Card 2) is one of
>the options available for the Cisco 6500 (and a couple of others, I think)
>switches.  When the switch receives a packet bound for a different VLAN, it
>sends it to the RP.  The RP makes the routing decision and puts an entry in
>the route cache for the switch.  The first packet in a flow is routed and
>the rest are switched at wire speed, hence the increase in speed.  That's
>kind of a simplified view, but I think it gets the general idea across.  So,
>layer 3 switching is both routing and switching, but faster (usually,
>anyway).

One should keep in mind that many vendors including Cisco have been capable 
of doing per packet routing at wire speed for some time and thus this 
"advantage" is a legacy attribute.



>""DeVoe, Charles (PKI)""  wrote in message
>news:200302251554.PAA06930@xxxxxxxxxxxxxxxxx
> > I am under the impression that switching is a layer 2 function and that
> > routing is a layer 3 function.  I have seen several discussions talking
> > about layer 3 switching.  Could someone explain this to me?




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