At 4:36 AM +0000 3/13/03, The Long and Winding Road wrote: >The problem with this whole discussion is that it focuses around hardware >that has been defined as something by the manufacturers, and does not focus >on function.
I tried. I really tried not to rejoin this never ending thread. But maybe there's one more contribution. For those of you that insist switches route in hardware, and routers route in software, I'd challenge you to look, in detail, at the hardware used. Believe it or not, an ASIC of the level of sophistication that can do forwarding is, in fact, a specialized and to some extent programmable processor. It might be an architecture simpler than many peoples' idea of RISC, such as a FPGA or microcode sequencer, but it's still usually a von Neumann architecture with separate code and execution. The code may very well be burned into a large integrated chip or chipset along with the processor, so that instructions are already decoded and don't need to flow outside the chip. But it definitely isn't "pure hardware," whatever that may be. I can only point to my work on control plane convergence in the IETF BMWG, and the work in the FORCES WG on control/forwarding plane separation, to suggest that no serious router designer thinks in terms of level 3 switches. It is purely a marketing term, perhaps with some very limited meaning in describing certain speed/feed/performance/cost regions. It also may indicate a class of devices that give up other functionality to get "wire speed forwarding"--and then gets used in environments where pure forwarding speed is not the make-or-break performance criterion. I do have a 3 layer CAT switch next to my monitor, which also serves the higher layer function of scratching post. At the moment, Ding is asleep on layer 3, but its layer 2 and 1 are not configured. Mr. Clark, who generally exceeds the port size of this switch, is sleeping in a favorite box on top of a file cabinet. Rhonda is perhaps dealing with upper-layer multimedia protocols, as she is sleeping in the document feeder of the fax machine. > >In the end, it is software - code - that does what it does, and the hardware >it runs on is irrelevant. > >The OSI model is just a way of looking at things. Even Cisco says as much. >OSI is not a hard and fast rule about how thing have to work. > >If an action is taken based on the IP header info, it is L3. If action is >taken based on ethernet header info, it is L2. > >How that action is coded, where that code resides, is irrelevant. > >JMHO > >-- >TANSTAAFL >"there ain't no such thing as a free lunch" > > > > >""aletoledo"" wrote in message >news:[EMAIL PROTECTED] >> a "layer three switch" is a router, just as a "switch" is really a bridge. >a >> layer 3 switch 'routes' in hardware, while a router routes in software. >> >> thats the easiest way to look at them. it has gaps, but once you get the >big >> picture you can then start to talk about the specifics. >> >> probably the biggest thing that a layer 3 switch can't do (unless its >> changed recently) is route anything but IP. while designing the hardware >> routing circuits for a L3-switch they had to compromise and IP being the >> most popular won out. thats not to say that one day they won't have made >> enough chipsets to route every other kind of protocol also. I suppose >since >> we saw the death of bridges due to switches, we'll also see the death of >> routers to L3-switch. >> >> scott >> >> ""nanda"" wrote in message >> news:[EMAIL PROTECTED] >> > Hi ... >> > >> > We have switches that operate at Layer 3..right.. >> > My Question is when we have Routers that are good enough why do we need >> > switches at layer3? >> > Under what circumtances do we use switches instead of routers? >> > >> > Hope I made Myself Clear...Thanks in Advance!!! >> > >> > Regards... >> > Nanda Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=65275&t=65215 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
