Ok all I have a question on this subject.  I know routing takes place at 
the network layer, and switching takes place at the data link layer 
because it works based on physical addresses.  So how do we get route 
switching?  I've just started my CCNP and we were learning about 
different cache methods to speed up performance, is this how route 
switching is done, is the routing calculation be performed on a per 
packet basis?  I was reading that by default, Cisco routers only perform 
a routing calculation on the first packet for a destination network and 
then on less the no route-cache option is set all the rest of the 
packets are really only "switched" to the correct interface.  Am I 
missing something?  I would invision that a router would by default 
perform a lookup for each connection sequence.  does layer 3 routing not 
do a look up for each sequence of packet?  Does is look at an address 
and use an "old" pre say route that was cached in memory?  If some one 
can give a good explanation I would greatly appreciate it.

Thanks,
Steve




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