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-----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of Howard C. Berkowitz Sent: Tuesday, February 18, 2003 6:42 AM To: [EMAIL PROTECTED] Subject: Re: Does MLS (Layer 3 switching) require VLANs? [7:63147] At 5:30 AM +0000 2/18/03, Ken Diliberto wrote: >The nit I'm picking is inline... (I'm feeling like chipping in tonight) > >>>> "The Long and Winding Road" >02/17/03 06:13PM >>> > >[snip] > >if I have a 75xx router with 300 ethernet ports, and I bridge all >those >ports, do I have an L3 switch, or a router? > >[KD] >You have a router performing L2 operations (forwarding, switching, >bridging -- whatever). Would a cheap Linksys switch be faster? > >What makes a L3 switch in my mind is where the forwarding happens. If >the L3 CPU (new way to look at it?) has to handle every packet, that's a >router. If the first L3 packet is handled by the CPU which then >programs ASICs to handle the rest of the flow without bothering the CPU, >that's an L3 switch. Is there a difference from a packet/network >perspective? No. The L2 headers and L3 headers are all properly >updated in both cases (at least we *hope* they are) and traffic is >delivered most of the time. (If it was delivered all the time, networks >wouldn't need us to fix them) :-) Does that make a 7500 with VIPs a L3 switch? A 12000 with distributed forwarding processors? ------------------------------ it depends....call it (d)cef switching router if you want but i have to kinda agree with ken's comments. in my opinion the major difference between a tradition router and a l3 switch is the way packet switching takes place. in a tradition router the packet switching are done in software (microprocessor based), whereas in l3 switch it is done by asic in hw and mls is used to increase routing performance by doing packet switching and rewrites in hw (asics). that's all. regards, /vicky Substituting router for L3 switch is a good idea, but go farther than that. You can think of a high-performance router as a small hidden network, containing one or more (think high availability) path determination "routing" processors/hosts that download FIB information to multiple forwarding processors/hosts. One public and vendor-independent discussion of this architecture continues in the IETF FORCES Working Group (go to www.ietf.org and navigate to Working Groups). > >What does this mean to us? Not much other than for capacity planning. >IMHO, an L3 switch has a longer life than a router. Not really, as you say in your next paragraph. I could go off into the ozone and say all high-speed routers are L3 switches. Indeed, ASICs aren't a necessity. I've worked on research router designs that used RISC processors in each forwarding and path determination engine, which gave lots of power but much more flexibility than ASICs. Admittedly, at least one of these was a specifically designed processor, but it definitely was software loadable and ran a real time OS. ASIC gets blurry anyway, when you start getting into the pure hard-etched IC, field-programmable gate arrays, electrically alterable field-programmable gate arrays, microcode sequencers, etc. > >When I design networks, I don't think L3 switch. I think about routers >interconnecting L2 segments. I even draw them that way most of the >time. :-) > >My advice to those having problems with this subject: Replace every >occurrence of "layer 3 switch" with "router". > [/KD] Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=63372&t=63147 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
