Just to follow up what Chuck said, understand that the "Layer-3 Switching" phenomena is a means of countering the performance penalty commonly associated with Network layer forwarding, as compared to Data-link layer forwarding.
The practical reality used to be that bridging/switching was faster than routing. Much of this was due to the implementation of the forwarding mechanism being moved to hardware in the form of ASICs (Application Specific Integrated Circuits). Layer-3 switching solutions have reduced the "Routing penalty" by again moving some of the forwarding mechanism to hardware... The basic difference is that a switch used to cache the MAC infomation only... Now, in a Layer-3 enabled switch, it caches both the MAC information, and the IP information for each connected device. In essence, the switch now acts as a router, but can do packet forwarding at near wire-speed, a claim that traditional routers could not boast. ----- Original Message ----- From: "Chuck Larrieu" To: Sent: Thursday, December 06, 2001 6:01 PM Subject: RE: What's the critical difference between level 3 switching > so says the market speak. > > in terms of how things really work, it makes not > one whit of difference how the forwarding cache > is constructed. look at bits C through D to determine > the MAC or bits A through B to determine the IP > address. The processor can do either one about as > fast. The layer three header still has to be stripped > before placing the packet on the local wire, which > operates at the MAC layer anyway. > > so my cache can say that MAC aaaa.aaaa.aaaa is > out port 4 or it can say 192.168.1.1 is out port 4. > No difference. I'm guessing the gains here are in > that a separate lookup or process does not have > to be involved, meaning there is a performance > enhancement if "layer 3" switching is used. > > as far as placing the packet onto the local wire, > it shouldn't matter. > > Chuck Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=28414&t=28414 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
