If the L3 switches are available and they can do the work of router at wire speed. Then why we still use router in the network? any one please give the answer with technical explanation.

http://en.wikipedia.org/wiki/Layer_... "the basic difference being processing speed and/or the way they do the switching; Level 3 switches use ASICs/hardware instead of the CPU/software that a router would"

Routers generally support different types of interfaces than a layer 3 switch might not like atm,bri , serial etc ... A lot of companies are going to a managed service where carriers like AT&T just drop off a fastethernet interface for you to plug into in which case you do not need a router and would be better off using a L3 switch , that being said though sometimes a lower end router is going to be cheaper , along with a layer 2 only switch hooked off the end , you pay for having both functions in one box. Routers are generally used for attaching to the WAN . The WAN will always be your bottle neck because usually you don't have more than say 45 meg as a pipe coming in (unless your company is rich) which is far less than most even layer 2 only switches can send the data so do you gain much by using a layer 3 switch attached to your wan , I would say probably not . It does simplify your installation as you have one less box you have to worry about.

There is no clear answer really anymore. YES, some smart switches are in fact true routers. By definition a Layer 3 switch would only care about layer 3 traffic where a modern router is at least layer 5 or sometimes called 5+ or 6+ or even 7+ switch or router. Wirespeed is another issue. As with all things, if you need to route and you need to do it well then get a router. If you need a switch and you don't care if the router part is a bit slow or doesn't have the bells then it might suit your needs. I read it wrong and answer it wrong too. So get off my case you peanut.

If the L3 switches are available and they can do the work of router at wire speed. Then why we still use router in the network? What you would choose to use would depend a whole lot on the size and complexity of your network. If you're talking about a small office with 20 PC's, you hardly need a layer 3 switch right. In fact, in that case, you'd probably go with a low-end, unmanaged switch coupled with a SOHO router. If you had a small to medium size network with say, 100 PC's, and you have need for subnetting/VLAN tagging, then you would probably give serious consideration to an enterprise level L3 switch (or switches, as the case may be). These could handle your routing as there would be a minimal amount. The environment I work in is huge. We have 8 remote sites encompassing 4 locations. Which is to say, our main location has 3 subsidiary sites as well as our main center. We have another location with a subsidiary site and then two more locations. The sub's are connected to the main location in their area via a wireless point-to-point shot (again, enterprise level equipment). We have several hundred users (staff - that's not including the hundres and thousands of remote users accessing our website and other resources), numerous printers, scanners, photocopiers and pretty much any network device you can think up. Our main center has a datacenter supporting over 100 servers and dual redundant core switches (yes, L3 capable). We VLAN tag extensively as we have many many subnets (at this point in time, roughly 50 subnets but that's growing all the time). You wouldn't try to do your routing in our case with just L3 switches. We do however handle the internal routing in our main location with our core switches. But we don't do all our routing with them. External routing all runs through OpenBSD based teamed (redundant) servers that are both our firewalls and our routers. The amount of data traversing our network at any one time requires very robust routers that can handle the work load. We VLAN extensively since this reduces routing and the time packets spend inside the routers. Another point to consider is flexibility. A layer 3 switch does not have all the features available in a real router. You wouldn't try to establish a BGP based multi-site WAN with L3 switches. They don't have the capability. At least, none of the ones I've worked with do...and I've worked with Cisco, Alcatel, 3Com and Nortel (my personal favorite, the Nortel Baystack high density 55x0 series).

Thanks a lot to all replies.