Re: Layer 3 Switches Vs Routers [7:65215]
In the end, the device either routes or bridges the frames it receives, but takes no action that can be distinctly described as layer three switching. Pete to my basic understanding ALL routing has a switching component to it already, whether we're talking about regular routers or L3 switches. process switching, fast switching, autonomous switching, distributed switching, etc... are all the ways the packets are moved between interfaces on a router. therefore both layer 2 and layer 3 'switch' irregardless of the name on the chassis. I personally view the sole distinction between the standard routers/bridges and the multilayer switches as the use of ASICs. scott Message Posted at: http://www.groupstudy.com/form/read.php?f=7i=65449t=65215 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
Re: Layer 3 Switches Vs Routers [7:65215]
At 5:57 PM + 3/14/03, Scott Roberts wrote: In the end, the device either routes or bridges the frames it receives, but takes no action that can be distinctly described as layer three switching. Pete to my basic understanding ALL routing has a switching component to it already, whether we're talking about regular routers or L3 switches. Correct for the Cisco product line. We do have some cases, especially in the service providers, where we have things like Route Servers. These speak BGP and manipulate and readvertise routing information, but have zero forwarding capability. These were once important in scaling eBGP at exchange points, but, as router processors have become more powerful, route servers are used more for traffic monitoring and research functions. RsD is one publically available implementation of a route server; it is a GateD derivative that runs on assorted *NIX platforms. There are also routing-only (i.e., forwarding free) devices used as protocol test and benchmark instruments. See http://www.ietf.org/internet-drafts/draft-ietf-bmwg-conterm-04.txt for a BGP-specific discussion. process switching, fast switching, autonomous switching, distributed switching, etc... are all the ways the packets are moved between interfaces on a router. therefore both layer 2 and layer 3 'switch' irregardless of the name on the chassis. I personally view the sole distinction between the standard routers/bridges and the multilayer switches as the use of ASICs. People may gain a lot more insight if they go beyond the initial, marketingspeak of oh, it's an ASIC and actually understood what is _in_ an ASIC. Most routing ASICs have processor, memories, etc., just as does the main processor. They do tend to have specialized instruction sets, minimum memory access time because their RAM is on-chip or on-chipset, don't spend time doing instruction decode (unless they already are microcode sequencers), etc. A sufficiently fast RISC processing system may be as fast or faster than an early routing ASIC. The local memory in an ASIC can be a double-edged sword when you are doing things like multicasting, and no memory is shared among forwarding processors. Message Posted at: http://www.groupstudy.com/form/read.php?f=7i=65466t=65215 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
Re: Layer 3 Switches Vs Routers [7:65215]
At 05:57 PM 3/14/2003 +, Scott Roberts wrote: In the end, the device either routes or bridges the frames it receives, but takes no action that can be distinctly described as layer three switching. Pete to my basic understanding ALL routing has a switching component to it already, whether we're talking about regular routers or L3 switches. process switching, fast switching, autonomous switching, distributed switching, etc... are all the ways the packets are moved between interfaces on a router. therefore both layer 2 and layer 3 'switch' irregardless of the name on the chassis. I disagree. You are describing a generic technology with vendor specific terminology. How packets move (if they move at all) in a router is an implementation specific detail (that is to say it's up to the box designer and internal to the device itself) . I personally view the sole distinction between the standard routers/bridges and the multilayer switches as the use of ASICs. How a technology is implemented does not change the nature of the technology itself. By this definition, I would be curious at what forwarding rate does a router becomes a switch? In other words, just because some IP routers are faster than others does not mean they are not routers. Of note, most high end routers implement an all silicon based forwarding path and few of these folks have branded their routers as switches. scott Message Posted at: http://www.groupstudy.com/form/read.php?f=7i=65476t=65215 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
Re: Layer 3 Switches Vs Routers [7:65215]
At 4:36 AM + 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=7i=65275t=65215 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
Re: Layer 3 Switches Vs Routers [7:65215]
At 01:43 AM 3/13/2003 +, aletoledo wrote: 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. For what its worth, Juniper would likely take exception to your calling their products layer three switches as they have an all ASIC forwarding plane and therefore route in hardware. 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=7i=65300t=65215 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
RE: Layer 3 Switches Vs Routers [7:65215]
At 10:44 PM 3/12/2003 +, Orlando, Jr. Palomar wrote: Without consulting any documentation, a couple of reasons I could think of is forwarding rate and the switch-fabric (or the size of the backplane, usually in Gbps). A full-fledged Layer-3 switch running at wire-speed would be much more efficient in routing (and switching) between VLANs compared to a router. Many routers route at wire speed and can do this on/between tagged VLANs. This is just routing. Another point of comparison is port density. You can only have such and such number of ethernet, fastethernet, or maybe even gigabit ethernet ports on a router before the cost becomes quite prohibitive. Oh sure, you can use the router-on-a-stick method. And though it is a good Cisco IOS feature, it was meant to be an interim solution when transitioning from a flat to a segmented network. Anyway, if you only have a relatively small network, say 2 VLANs, you can opt for the router-on-a-stick method. Or better yet, use a router with dual ethernets or fastethernets. However, if you're supporting 4,5, or more networks, that's what L-3 and multi-layer switches are for. Message Posted at: http://www.groupstudy.com/form/read.php?f=7i=65301t=65215 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
RE: Layer 3 Switches Vs Routers [7:65215]
At 12:16 PM 3/13/2003 -0500, Howard C. Berkowitz wrote: At 2:43 PM + 3/13/03, Peter van Oene wrote: At 10:44 PM 3/12/2003 +, Orlando, Jr. Palomar wrote: Without consulting any documentation, a couple of reasons I could think of is forwarding rate and the switch-fabric (or the size of the backplane, usually in Gbps). A full-fledged Layer-3 switch running at wire-speed would be much more efficient in routing (and switching) between VLANs compared to a router. Many routers route at wire speed and can do this on/between tagged VLANs. This is just routing. Another point of comparison is port density. You can only have such and such number of ethernet, fastethernet, or maybe even gigabit ethernet ports on a router before the cost becomes quite prohibitive. Oh sure, you can use the router-on-a-stick method. And though it is a good Cisco IOS feature, it was meant to be an interim solution when transitioning from a flat to a segmented network. Anyway, if you only have a relatively small network, say 2 VLANs, you can opt for the router-on-a-stick method. Or better yet, use a router with dual ethernets or fastethernets. However, if you're supporting 4,5, or more networks, that's what L-3 and multi-layer switches are for. Peter, would you agree that when someone says that's what layer3 and multilayer switches are for, they are really talking about router packaging (as oppposed to fundamentally different technology) that creates platforms with certain port densities, functionality tradeoffs, and price points? I would certainly agree. There is definitely a family of enterprise devices that package relatively high density layer two aggregation (ie lots of GE/FE ports) with a routing functionality such that you end up with an integrated device that can route or bridge depending upon configuration. However, such a device is in theory no differently that a router connected directly to a bridge via an external vlan trunked interface. The fact that the box happens to integrate the connection between router and bridge is merely a matter of convenience. In the end, the device either routes or bridges the frames it receives, but takes no action that can be distinctly described as layer three switching. Pete Again, I call attention to the comment of routing in hardware as misleading. I can't think of a routing ASIC, where I actually looked at the chip or chipset design, that wasn't some flavor of Von Neumann stored-program computer. Certain of the specific designs might be microcode rather than RISC or CISC, but they are still basically von Neumann. FPGAs might be a special case, but they can't do the more complex functions. In other words, an ASIC is a computer, just a specialized, optimized computer burned into silicon (or whatever).. Some newer ASICs even are partially reprogrammable, typically with electrically alterable gate arrays and the like. Message Posted at: http://www.groupstudy.com/form/read.php?f=7i=65341t=65215 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
RE: Layer 3 Switches Vs Routers [7:65215]
At 2:43 PM + 3/13/03, Peter van Oene wrote: At 10:44 PM 3/12/2003 +, Orlando, Jr. Palomar wrote: Without consulting any documentation, a couple of reasons I could think of is forwarding rate and the switch-fabric (or the size of the backplane, usually in Gbps). A full-fledged Layer-3 switch running at wire-speed would be much more efficient in routing (and switching) between VLANs compared to a router. Many routers route at wire speed and can do this on/between tagged VLANs. This is just routing. Another point of comparison is port density. You can only have such and such number of ethernet, fastethernet, or maybe even gigabit ethernet ports on a router before the cost becomes quite prohibitive. Oh sure, you can use the router-on-a-stick method. And though it is a good Cisco IOS feature, it was meant to be an interim solution when transitioning from a flat to a segmented network. Anyway, if you only have a relatively small network, say 2 VLANs, you can opt for the router-on-a-stick method. Or better yet, use a router with dual ethernets or fastethernets. However, if you're supporting 4,5, or more networks, that's what L-3 and multi-layer switches are for. Peter, would you agree that when someone says that's what layer3 and multilayer switches are for, they are really talking about router packaging (as oppposed to fundamentally different technology) that creates platforms with certain port densities, functionality tradeoffs, and price points? Again, I call attention to the comment of routing in hardware as misleading. I can't think of a routing ASIC, where I actually looked at the chip or chipset design, that wasn't some flavor of Von Neumann stored-program computer. Certain of the specific designs might be microcode rather than RISC or CISC, but they are still basically von Neumann. FPGAs might be a special case, but they can't do the more complex functions. In other words, an ASIC is a computer, just a specialized, optimized computer burned into silicon (or whatever).. Some newer ASICs even are partially reprogrammable, typically with electrically alterable gate arrays and the like. Message Posted at: http://www.groupstudy.com/form/read.php?f=7i=65330t=65215 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
Re: Layer 3 Switches Vs Routers [7:65215]
In the enterprise, I can vlan a building into seperate lans, route between them and connect all the users with the same box..Thats one reason for layer 3 switches.. With the inclusion of the switching module in the 3745 router box, it now kinda blurs the difference between routers and switches.. That box now can be a router for lan, wan, voice and a L2/L3 switch for a small office. Larry Letterman Network Engineer Cisco Systems - Original Message - From: nanda To: [EMAIL PROTECTED] Sent: Wednesday, March 12, 2003 1:31 PM Subject: Layer 3 Switches Vs Routers [7:65215] 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=7i=65238t=65215 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
RE: Layer 3 Switches Vs Routers [7:65215]
Without consulting any documentation, a couple of reasons I could think of is forwarding rate and the switch-fabric (or the size of the backplane, usually in Gbps). A full-fledged Layer-3 switch running at wire-speed would be much more efficient in routing (and switching) between VLANs compared to a router. Another point of comparison is port density. You can only have such and such number of ethernet, fastethernet, or maybe even gigabit ethernet ports on a router before the cost becomes quite prohibitive. Oh sure, you can use the router-on-a-stick method. And though it is a good Cisco IOS feature, it was meant to be an interim solution when transitioning from a flat to a segmented network. Anyway, if you only have a relatively small network, say 2 VLANs, you can opt for the router-on-a-stick method. Or better yet, use a router with dual ethernets or fastethernets. However, if you're supporting 4,5, or more networks, that's what L-3 and multi-layer switches are for. Message Posted at: http://www.groupstudy.com/form/read.php?f=7i=65221t=65215 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
Re: Layer 3 Switches Vs Routers [7:65215]
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=7i=65242t=65215 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
Re: Layer 3 Switches Vs Routers [7:65215]
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. 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=7i=65255t=65215 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
