Hi
This is a generalisation for the low end switches/routers (fx 3750 series) and you will always find examples that is not accurat with this generalisation.
that said as a general rule it will apply.
As a general rule the L3 switch is a fast router on a local lan or a metro ethernet connection..
Cons
It lacks the ability to route other protocols than IP and it has a limited memory available for routingtables and that type of information. It lacks full advanced routing and it can not contain fx NAT and firewall ruleset. It does not handle other types of connections than some variation of ethernet. it can not be memory upgraded
Pros
in a local lan that has no need for advanced routing protocols and can utilise fx static routing, ospf and so on they are a very trong alternative with many ports/svi that
It is very fast and affordable compared to a true router routing the same speed.
Router
Cons
Exspensive and slow (in comparision to L3 switch)
Pros
It can utilise any form of connection, (serial links, ethernet and so on)
It can utilise things like NAT, firewalling, ids, netflow and such features (think I saw a figure of over 200 feature types)
It can have large routing tables.
It can utilise many different types of routing protocols
It can utilise many types of protocols other than ip (fx ipx/spx and so on)
It is expandable (ram memory and flash)
It is expandable by using different expansion cards.
so to short it out you can say
L3 switch is fast and inexpensive but does not know to much. the reason it is fast is because it does not have to be smart and that is the reason you can do alot of things in the ASICS (with hardware) instead of in the CPU (with software)
Router is slow and expensive but knows and can handle a lot. The knowing and handeling alot of diffferent variables, is very dynamic and thus made in software (CPU).
Good luck
HTH
