Re: L3 Switching Huh???? [7:63728]
Layer 3 switching combines the best of switching and routing in one platform. The main advantage here is speed. The way it works is, in a switch you have some kind of layer 3 routing engine (aka route processor, or RP). For example, the MSFC2 (Multilayer Switch Feature Card 2) is one of the options available for the Cisco 6500 (and a couple of others, I think) switches. When the switch receives a packet bound for a different VLAN, it sends it to the RP. The RP makes the routing decision and puts an entry in the route cache for the switch. The first packet in a flow is routed and the rest are switched at wire speed, hence the increase in speed. That's kind of a simplified view, but I think it gets the general idea across. So, layer 3 switching is both routing and switching, but faster (usually, anyway). ""DeVoe, Charles (PKI)"" wrote in message news:[EMAIL PROTECTED] > I am under the impression that switching is a layer 2 function and that > routing is a layer 3 function. I have seen several discussions talking > about layer 3 switching. Could someone explain this to me? Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=63738&t=63728 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
Re: L3 Switching Huh???? [7:63728]
At 03:54 PM 2/25/2003 +, DeVoe, Charles (PKI) wrote: >I am under the impression that switching is a layer 2 function and that >routing is a layer 3 function. I have seen several discussions talking >about layer 3 switching. Could someone explain this to me? Bridging is a layer two function, routing is a layer three function. Switching is an ambiguous term and should be avoided in technical conversations. Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=63746&t=63728 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
RE: L3 Switching Huh???? [7:63728]
According to Cisco: Layer 3 switching refers to a class of high-performance switch routers optimized for the campus LAN or intranet, providing wirespeed Ethernet routing and switching services. Compared to other routers, Layer 3 switch routers process more packets faster by using application-specific integrated circuit (ASIC) hardware instead of microprocessor-based engines. My own two cents: Wire speed routing if you will. Drew -Original Message- From: DeVoe, Charles (PKI) [mailto:[EMAIL PROTECTED] Sent: Tuesday, February 25, 2003 10:55 AM To: [EMAIL PROTECTED] Subject: L3 Switching Huh [7:63728] I am under the impression that switching is a layer 2 function and that routing is a layer 3 function. I have seen several discussions talking about layer 3 switching. Could someone explain this to me? Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=63753&t=63728 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
Re: L3 Switching Huh???? [7:63728]
There are two scenario's discussed here, and I am sure I'll be corrected by everyone... Multi layer switching version means that the first packet in a flow of data will be routed the usual way in the ios software, then the rest of the packets in the flow will be hardware switched from L2 port thru the switch to the destination L2 port. The other L3 terminology means that the switch can function as a L3 router or a L2 switch with the same hardware and that you can configure each port as a L2 or L3 port/interface and that the IOS supports most of the L3 routing protocols, examples- 2948G, 3550-EMI, 400X, 5000,6509 Corrections anybody ? Larry Letterman Network Engineer Cisco Systems - Original Message - From: "DeVoe, Charles (PKI)" To: Sent: Tuesday, February 25, 2003 7:54 AM Subject: L3 Switching Huh [7:63728] > I am under the impression that switching is a layer 2 function and that > routing is a layer 3 function. I have seen several discussions talking > about layer 3 switching. Could someone explain this to me? [EMAIL PROTECTED] Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=63754&t=63728 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
Re: L3 Switching Huh???? [7:63728]
Switching is the function of directing frames or packets from one port or interface to another. A layer 3 switch, switches packets at wire speed using ASICs. An example would be the 8500 series. >From: "DeVoe, Charles (PKI)" >Reply-To: "DeVoe, Charles (PKI)" >To: [EMAIL PROTECTED] >Subject: L3 Switching Huh [7:63728] >Date: Tue, 25 Feb 2003 15:54:56 GMT > >I am under the impression that switching is a layer 2 function and that >routing is a layer 3 function. I have seen several discussions talking >about layer 3 switching. Could someone explain this to me? _ MSN 8 helps eliminate e-mail viruses. Get 2 months FREE*. http://join.msn.com/?page=features/virus Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=63755&t=63728 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
Re: L3 Switching Huh???? [7:63728]
More or less in one word, marketing!! Dave DeVoe, Charles (PKI) wrote: > I am under the impression that switching is a layer 2 function and that > routing is a layer 3 function. I have seen several discussions talking > about layer 3 switching. Could someone explain this to me? -- David Madland CCIE# 2016 Sr. Network Engineer Qwest Communications 612-664-3367 "You don't make the poor richer by making the rich poorer." --Winston Churchill Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=63757&t=63728 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
Re: L3 Switching Huh???? [7:63728]
At 3:54 PM + 2/25/03, DeVoe, Charles (PKI) wrote: >I am under the impression that switching is a layer 2 function and that >routing is a layer 3 function. I have seen several discussions talking >about layer 3 switching. Could someone explain this to me? The bottom line is that layer 3 switching _is_ routing. There is a great deal of marketing FUD that waves hands in the direction "switch fast router slow." Not a useful distinction until you talk about specific requirements and specific product implementations. Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=63759&t=63728 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
Re: L3 Switching Huh???? [7:63728]
Robert Edmonds wrote: > > Layer 3 switching combines the best of switching and routing in > one > platform. The main advantage here is speed. The way it works > is, in a > switch you have some kind of layer 3 routing engine (aka route > processor, or > RP). For example, the MSFC2 (Multilayer Switch Feature Card 2) > is one of > the options available for the Cisco 6500 (and a couple of > others, I think) > switches. When the switch receives a packet bound for a > different VLAN, it > sends it to the RP. The decision to send to the RP isn't really based on the VLAN is it?? The decision is based on the MAC destination address, I would assume. A host in VLAN 1 wants to send to a host in VLAN 2. Because VLANs generally equate to IP subnets, the host knows that it must send to its default gateway, which is the RP. It ARPs for the RP and gets a MAC address. It sends the frame then with the destinaton MAC address set to the RP's address. The L2 switch looks just at MAC addresses. That's what makes it L2. It has learned that this MAC address belongs to the RP. (Learning the location of MAC addresses is a basic L2 function). Now the RP can do L3 "switching." It looks at the IP destination address to determine where to send the frame. That's what makes it L3 (i.e. that it uses a L3 address for its decision). As far as switching, routing, forwarding, they all mean the same thing. As Kevin Banifaz said in one of the best, most concise answers that we have seen, "Switching is the function of directing frames or packets from one port or interface to another." Someone said that switching isn't a technical term. What a shame. It certainly used to be a good engineering term. Network equipment developers borrowed the term from our forefathers and foremathers who worked on the high-tech equipment of the 1800s and 1900s. Railroad tracks switch trains. Electrical equipment switches current. Telephone equipment switches voice conversations. Bridges, switches, and routers switch frames. I must direct you all, once again it seems, to Webster's definition of switch, the noun: Main Entry: 1switch Pronunciation: 'swich Function: noun Etymology: perhaps from Middle Dutch swijch twig Date: 1592 1 : a slender flexible whip, rod, or twig 2 : an act of switching : as a : a blow with a switch b : a shift from one to another c : a change from the usual 3 : a tuft of long hairs at the end of the tail of an animal (as a cow) -- see COW illustration 4 a : a device made usually of two movable rails and necessary connections and designed to turn a locomotive or train from one track to another b : a railroad siding 5 : a device for making, breaking, or changing the connections in an electrical circuit 6 : a heavy strand of hair used in addition to a person's own hair for some coiffures If anyone else brings up this question, we may need to have definition 1 applied to them. Or, if we're nice, we'll use definition 6 on your behind instead. Or we'll say that you are definition 3. :-) Priscilla > The RP makes the routing decision and puts > an entry in > the route cache for the switch. The first packet in a flow is > routed and > the rest are switched at wire speed, hence the increase in > speed. That's > kind of a simplified view, but I think it gets the general idea > across. So, > layer 3 switching is both routing and switching, but faster > (usually, > anyway). > > ""DeVoe, Charles (PKI)"" wrote in > message > news:[EMAIL PROTECTED] > > I am under the impression that switching is a layer 2 > function and that > > routing is a layer 3 function. I have seen several > discussions talking > > about layer 3 switching. Could someone explain this to me? > > Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=63762&t=63728 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
Re: L3 Switching Huh???? [7:63728]
At 4:46 PM + 2/25/03, Robert Edmonds wrote: >Layer 3 switching combines the best of switching and routing in one >platform. It isn't the best of both worlds, because raw forwarding speed is frequently not the constraint on real-world network design. From a cost standpoint, it would be completely insane to put high-performance devices of this type into branch offices. Fast is only one component of a design solution. Before people start worrying about being wire speed or not, look at the requirements. If you choose to put in Gig E simply because your servers can, hypothetically, service 200 Mbps of traffic and you don't want to use Etherchannel, it's irrelevant if you can forward at Gig E speed -- it won't buy you anything. Server interface bandwidth, in my experience, is far more often to be the limiting factor than delay in the forwarding elements, be they routers, switches, layer 2 routers, layer 3 switches, or what have you. Tailor the platform for the job. For example, the 7200 has a DS-3 interface, but (and I'd have to check on the latest NPE specs), historically it can't fill that interface. With typical US pricing, however, the breakeven point between link cost alone (i.e., not considering additional router interfaces) for multiple DS-1 versus fractional use of a DS-3 is around 6-7 DS-1's. That the DS-3 could carry 28 DS-1's if the router could do "wire speed" is irrelevant to the problem. Having the ability to PHYSICALLY INTERFACE to a high-speed facility may be a much more important cost factor than having that interface run at "wire speed." There are other approaches to network speedup rather than accelerating the forwarding rate. I've frequently improved a network by providing a separate L2 switched LAN for backup or synchronization among colocated servers, putting an extra NIC into these servers. We did this before we knew to call that a Storage Area Network. ;-) >The main advantage here is speed. The way it works is, in a >switch you have some kind of layer 3 routing engine (aka route processor, or >RP). For example, the MSFC2 (Multilayer Switch Feature Card 2) is one of >the options available for the Cisco 6500 (and a couple of others, I think) >switches. When the switch receives a packet bound for a different VLAN, it >sends it to the RP. The RP makes the routing decision and puts an entry in >the route cache for the switch. The first packet in a flow is routed and >the rest are switched at wire speed, hence the increase in speed. That's >kind of a simplified view, but I think it gets the general idea across. So, >layer 3 switching is both routing and switching, but faster (usually, >anyway). > >""DeVoe, Charles (PKI)"" wrote in message >news:[EMAIL PROTECTED] >> I am under the impression that switching is a layer 2 function and that >> routing is a layer 3 function. I have seen several discussions talking > > about layer 3 switching. Could someone explain this to me? Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=63764&t=63728 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
Re: L3 Switching Huh???? [7:63728]
Charles, Regarding the meaning of the term "switch", let me quote a few lines from my favorite Net Goddess, Radia Perlman. She wrote the DEC STP protocol and has been very active in protocol development since day one. In her book, Interconnections, she says the following: "One cynical (and ungrammatical) definition I use for switch is 'a marketing term that means fast'" p. 127 She goes on to suggest that the term switch should be used for "a box that moves data." She further suggests that we get into the habit of specifying as follows: Layer 1 switch = hub Layer 2 switch = bridge Layer 3 switch = router Strongly recommend her book. The lady has a lot of style. -HTH -Bob Sinclair CCIE #10427 - Original Message - From: "DeVoe, Charles (PKI)" To: Sent: Tuesday, February 25, 2003 10:54 AM Subject: L3 Switching Huh [7:63728] > I am under the impression that switching is a layer 2 function and that > routing is a layer 3 function. I have seen several discussions talking > about layer 3 switching. Could someone explain this to me? Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=63770&t=63728 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
RE: L3 Switching Huh???? [7:63728]
The decision to send to the RP isn't really based on the VLAN is it?? I believe that the decision to send to the Routing Processor (RP) is indeed based on the VLAN. When a host wishes to communicate with another host, the IP on the host determines if the host is on the same subnet or not. If it is on the same subnet, it will send an ARP broadcast to determine the MAC address of the destination host. If the host is on another subnet, the ARP request will be for that of the default gateway (aka RP). The RP will strip out the source and destination MAC address and replace the destination with that of host B (or next hop) and place it's own MAC address in the source address. The IP addresses will not be changed. Switches and Bridges make decisions based on MAC address (layer 2). Routers make decisions based on IP address (layer 3). So is the RP making routing decisions based on the MAC address??? -Original Message- From: Priscilla Oppenheimer [mailto:[EMAIL PROTECTED] Sent: Tuesday, February 25, 2003 1:33 PM To: [EMAIL PROTECTED] Subject: Re: L3 Switching Huh???? [7:63728] Robert Edmonds wrote: > > Layer 3 switching combines the best of switching and routing in > one > platform. The main advantage here is speed. The way it works > is, in a > switch you have some kind of layer 3 routing engine (aka route > processor, or > RP). For example, the MSFC2 (Multilayer Switch Feature Card 2) > is one of > the options available for the Cisco 6500 (and a couple of > others, I think) > switches. When the switch receives a packet bound for a > different VLAN, it > sends it to the RP. The decision to send to the RP isn't really based on the VLAN is it?? The decision is based on the MAC destination address, I would assume. A host in VLAN 1 wants to send to a host in VLAN 2. Because VLANs generally equate to IP subnets, the host knows that it must send to its default gateway, which is the RP. It ARPs for the RP and gets a MAC address. It sends the frame then with the destinaton MAC address set to the RP's address. The L2 switch looks just at MAC addresses. That's what makes it L2. It has learned that this MAC address belongs to the RP. (Learning the location of MAC addresses is a basic L2 function). Now the RP can do L3 "switching." It looks at the IP destination address to determine where to send the frame. That's what makes it L3 (i.e. that it uses a L3 address for its decision). As far as switching, routing, forwarding, they all mean the same thing. As Kevin Banifaz said in one of the best, most concise answers that we have seen, "Switching is the function of directing frames or packets from one port or interface to another." Someone said that switching isn't a technical term. What a shame. It certainly used to be a good engineering term. Network equipment developers borrowed the term from our forefathers and foremathers who worked on the high-tech equipment of the 1800s and 1900s. Railroad tracks switch trains. Electrical equipment switches current. Telephone equipment switches voice conversations. Bridges, switches, and routers switch frames. I must direct you all, once again it seems, to Webster's definition of switch, the noun: Main Entry: 1switch Pronunciation: 'swich Function: noun Etymology: perhaps from Middle Dutch swijch twig Date: 1592 1 : a slender flexible whip, rod, or twig 2 : an act of switching : as a : a blow with a switch b : a shift from one to another c : a change from the usual 3 : a tuft of long hairs at the end of the tail of an animal (as a cow) -- see COW illustration 4 a : a device made usually of two movable rails and necessary connections and designed to turn a locomotive or train from one track to another b : a railroad siding 5 : a device for making, breaking, or changing the connections in an electrical circuit 6 : a heavy strand of hair used in addition to a person's own hair for some coiffures If anyone else brings up this question, we may need to have definition 1 applied to them. Or, if we're nice, we'll use definition 6 on your behind instead. Or we'll say that you are definition 3. :-) Priscilla > The RP makes the routing decision and puts > an entry in > the route cache for the switch. The first packet in a flow is > routed and > the rest are switched at wire speed, hence the increase in > speed. That's > kind of a simplified view, but I think it gets the general idea > across. So, > layer 3 switching is both routing and switching, but faster > (usually, > anyway). > > ""DeVoe, Charles (PKI)"" wrote in > message > news:[EMAIL PROTECTED] > > I am under the impression that switching is a layer 2 > function and that > > routing is a layer 3 function. I have seen several > discussions talking > > about layer 3
Re: L3 Switching Huh???? [7:63728]
May I suggest people consult RFC 1812 and http://www.ietf.org/html.charters/forces-charter.html before going off into marketing definitions of switching? Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=63781&t=63728 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
Re: L3 Switching Huh???? [7:63728]
At 04:46 PM 2/25/2003 +, Robert Edmonds wrote: >Layer 3 switching combines the best of switching and routing in one >platform. The main advantage here is speed. The way it works is, in a >switch you have some kind of layer 3 routing engine (aka route processor, or >RP). For example, the MSFC2 (Multilayer Switch Feature Card 2) is one of >the options available for the Cisco 6500 (and a couple of others, I think) >switches. When the switch receives a packet bound for a different VLAN, it >sends it to the RP. The RP makes the routing decision and puts an entry in >the route cache for the switch. The first packet in a flow is routed and >the rest are switched at wire speed, hence the increase in speed. That's >kind of a simplified view, but I think it gets the general idea across. So, >layer 3 switching is both routing and switching, but faster (usually, >anyway). One should keep in mind that many vendors including Cisco have been capable of doing per packet routing at wire speed for some time and thus this "advantage" is a legacy attribute. >""DeVoe, Charles (PKI)"" wrote in message >news:[EMAIL PROTECTED] > > I am under the impression that switching is a layer 2 function and that > > routing is a layer 3 function. I have seen several discussions talking > > about layer 3 switching. Could someone explain this to me? Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=63783&t=63728 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
RE: L3 Switching Huh???? [7:63728]
At 06:03 PM 2/25/2003 +, Ellis, Andrew wrote: >According to Cisco: > >Layer 3 switching refers to a class of high-performance switch routers >optimized for the campus LAN or intranet, providing wirespeed Ethernet >routing and switching services. > >Compared to other routers, Layer 3 switch routers process more packets >faster by using application-specific integrated circuit (ASIC) hardware >instead of microprocessor-based engines. > >My own two cents: Wire speed routing if you will. By that logic, a wire speed router is a layer three switch :-) It's all marketing garbage if you ask me. If you put a router inside a high performance switch, you have two devices sharing the same chassis, one bridging and one routing. >Drew > > >-Original Message- >From: DeVoe, Charles (PKI) [mailto:[EMAIL PROTECTED] >Sent: Tuesday, February 25, 2003 10:55 AM >To: [EMAIL PROTECTED] >Subject: L3 Switching Huh [7:63728] > > >I am under the impression that switching is a layer 2 function and that >routing is a layer 3 function. I have seen several discussions talking >about layer 3 switching. Could someone explain this to me? Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=63785&t=63728 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
Re: L3 Switching Huh???? [7:63728]
At 7:34 PM + 2/25/03, Bob Sinclair wrote: >Charles, > >Regarding the meaning of the term "switch", let me quote a few lines from >my favorite Net Goddess, Radia Perlman. She wrote the DEC STP protocol and >has been very active in protocol development since day one. In her book, >Interconnections, she says the following: > >"One cynical (and ungrammatical) definition I use for switch is 'a marketing >term that means fast'" p. 127 > >She goes on to suggest that the term switch should be used for "a box that >moves data." Seriously, the preferred IETF approach is to deal separately with control (e.g., routing protocol) and forwarding planes. Control planes populate RIBs optimized for updating by routing protocols, and create FIBs optimized for doing fast destination lookup on forwarding elements. > >She further suggests that we get into the habit of specifying as follows: > >Layer 1 switch = hub >Layer 2 switch = bridge >Layer 3 switch = router > >Strongly recommend her book. The lady has a lot of style. > I don't remember if she's still doing a protocol design seminar as she used to do at Interop, but she's a delightful speaker, once you get used to the idea of somebody being a stereotyped New York Jewish Mother nagging packets. Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=63794&t=63728 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
RE: L3 Switching Huh???? [7:63728]
DeVoe, Charles (PKI) wrote: > > The decision to send to the RP isn't really based on the VLAN > is it?? > > I believe that the decision to send to the Routing Processor > (RP) is indeed > based on the VLAN. When a host wishes to communicate with > another host, the > IP on the host determines if the host is on the same subnet or > not. If it > is on the same subnet, it will send an ARP broadcast to > determine the MAC > address of the destination host. If the host is on another > subnet, the ARP > request will be for that of the default gateway (aka RP). The > RP will strip > out the source and destination MAC address and replace the > destination with > that of host B (or next hop) and place its own MAC address in > the source > address. The IP addresses will not be changed. You jumped from the ARP to the actual packet. You also jumped to a conclusion that the switch knows to send the packet to the RP because of the VLAN? (That was the language I was disputing). The switch knows because of the destination MAC address. Also, and this is the most critical, you skipped the step whereby the RP knows which interface it should use for sending the packet and which destination MAC address it should use. It knows that because it looks in its routing table or cache for the destination IP address in the packet. That allows it to figure out the outgoing interface and send directly to the recipient or the next hop. In other words it does Layer 3 switching, aka routing, forwarding, relaying. It bases its forwarding decision on the IP address. Networking 101. Extremely silly to be arguing about this. Here's what happens: The RP responds to the ARP from the host that is trying to find a MAC address for its default gateway, which is configured as an IP address. (We're assuming the mapping of the default gateway IP address to MAC address is no longer in the host's ARP table. If it were, the ARP wouldn't happen.) The host then sends the actual packet that resulted in it needing to send an ARP in the first place. It puts the default gateway's MAC address in the MAC destination field. It puts the end station's IP address in the IP destination field. So the RP (which we're assuming is the default gateway) takes in the frame, strips off the MAC header and looks at the destination IP address to determine how to send the frame. In other words, it does Layer 3 "switching," sometimes also called relaying, forwarding, or routing. If necessary, it will ARP to get the MAC address of the final destination (if it's local) or next-hop destination. > > Switches and Bridges make decisions based on MAC address (layer > 2). Routers > make decisions based on IP address (layer 3). > > So is the RP making routing decisions based on the MAC > address??? No, of course not. Priscilla > > > > > > -Original Message----- > From: Priscilla Oppenheimer [mailto:[EMAIL PROTECTED] > Sent: Tuesday, February 25, 2003 1:33 PM > To: [EMAIL PROTECTED] > Subject: Re: L3 Switching Huh [7:63728] > > > Robert Edmonds wrote: > > > > Layer 3 switching combines the best of switching and routing > in > > one > > platform. The main advantage here is speed. The way it works > > is, in a > > switch you have some kind of layer 3 routing engine (aka route > > processor, or > > RP). For example, the MSFC2 (Multilayer Switch Feature Card > 2) > > is one of > > the options available for the Cisco 6500 (and a couple of > > others, I think) > > switches. When the switch receives a packet bound for a > > different VLAN, it > > sends it to the RP. > > The decision to send to the RP isn't really based on the VLAN > is it?? The > decision is based on the MAC destination address, I would > assume. > > A host in VLAN 1 wants to send to a host in VLAN 2. Because > VLANs generally > equate to IP subnets, the host knows that it must send to its > default > gateway, which is the RP. It ARPs for the RP and gets a MAC > address. It > sends the frame then with the destinaton MAC address set to the > RP's > address. > > The L2 switch looks just at MAC addresses. That's what makes it > L2. It has > learned that this MAC address belongs to the RP. (Learning the > location of > MAC addresses is a basic L2 function). > > Now the RP can do L3 "switching." It looks at the IP > destination address to > determine where to send the frame. That's what makes it L3 > (i.e. that it > uses a L3 address for its decision). > > As far as switching, routing, forwarding, they all mean the > same thing. As > Kevin Banifaz said in one of the best, most concise answers >
Re: L3 Switching Huh???? [7:63728]
Howard C. Berkowitz wrote: > >Strongly recommend her book. The lady has a lot of style. > > > > I don't remember if she's still doing a protocol design seminar > as > she used to do at Interop, but she's a delightful speaker, once > you > get used to the idea of somebody being a stereotyped New York > Jewish > Mother nagging packets. I don't think Radia Perlman fits any stereotype, actually. She is a unique entity. I found out recently that her name is pronounced like radiate and radio, which I thought was perfect. She radiates intelligence, humor, cynicism, and earth-mother goddess. (Well, and maybe Jewish mother too! ;-) Priscilla > > Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=63800&t=63728 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
RE: L3 Switching Huh???? [7:63728]
How do you nag a packet? Infact, is it not an oxymoron? To nag is to continually pester or annoy, yet a packets lifetime is normally measured in milliseconds, therefore she must be one hell of a nagger! Ok, it's late, I'll stop. Symon -Original Message- From: Howard C. Berkowitz [mailto:[EMAIL PROTECTED] Sent: 25 February 2003 22:27 To: [EMAIL PROTECTED] Subject: Re: L3 Switching Huh???? [7:63728] At 7:34 PM + 2/25/03, Bob Sinclair wrote: >Charles, > >Regarding the meaning of the term "switch", let me quote a few lines >from my favorite Net Goddess, Radia Perlman. She wrote the DEC STP >protocol and has been very active in protocol development since day >one. In her book, Interconnections, she says the following: > >"One cynical (and ungrammatical) definition I use for switch is 'a marketing >term that means fast'" p. 127 > >She goes on to suggest that the term switch should be used for "a box >that moves data." Seriously, the preferred IETF approach is to deal separately with control (e.g., routing protocol) and forwarding planes. Control planes populate RIBs optimized for updating by routing protocols, and create FIBs optimized for doing fast destination lookup on forwarding elements. > >She further suggests that we get into the habit of specifying as >follows: > >Layer 1 switch = hub >Layer 2 switch = bridge >Layer 3 switch = router > >Strongly recommend her book. The lady has a lot of style. > I don't remember if she's still doing a protocol design seminar as she used to do at Interop, but she's a delightful speaker, once you get used to the idea of somebody being a stereotyped New York Jewish Mother nagging packets. = This email has been content filtered and subject to spam filtering. If you consider this email is unsolicited please forward the email to [EMAIL PROTECTED] and request that the sender's domain be blocked from sending any further emails. = Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=63810&t=63728 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
RE: L3 Switching Huh???? [7:63728]
Symon Thurlow wrote: > > How do you nag a packet? Infact, is it not an oxymoron? > > To nag is to continually pester or annoy, yet a packets > lifetime is > normally measured in milliseconds, therefore she must be one > hell of a > nagger! You can get a lot of nagging done in a millisecond! ;-) These days we have firewalls that have to understand TCP sequence and ACK numbers, for heaven's sake. And we have IDSs that look at the parameters to HTTP GET commands. Not to mention devices that switch packets based on payload content, i.e. a L7 switch!? Argh. And those are just a few of the stop-off points for a packet. I haven't even mentioned the routers and L2 switches!? All I can say is that it's a good thing we have so much bandwidth and such high-speed CPUs. Priscilla > > Ok, it's late, I'll stop. > > Symon > > -Original Message- > From: Howard C. Berkowitz [mailto:[EMAIL PROTECTED] > Sent: 25 February 2003 22:27 > To: [EMAIL PROTECTED] > Subject: Re: L3 Switching Huh [7:63728] > > > At 7:34 PM + 2/25/03, Bob Sinclair wrote: > >Charles, > > > >Regarding the meaning of the term "switch", let me quote a > few lines > >from my favorite Net Goddess, Radia Perlman. She wrote the > DEC STP > >protocol and has been very active in protocol development > since day > >one. In her book, Interconnections, she says the following: > > > >"One cynical (and ungrammatical) definition I use for switch > is 'a > marketing > >term that means fast'" p. 127 > > > >She goes on to suggest that the term switch should be used for > "a box > >that moves data." > > Seriously, the preferred IETF approach is to deal separately > with > control (e.g., routing protocol) and forwarding planes. Control > planes populate RIBs optimized for updating by routing > protocols, and > create FIBs optimized for doing fast destination lookup on > forwarding > elements. > > > > >She further suggests that we get into the habit of specifying > as > >follows: > > > >Layer 1 switch = hub > >Layer 2 switch = bridge > >Layer 3 switch = router > > > >Strongly recommend her book. The lady has a lot of style. > > > > I don't remember if she's still doing a protocol design seminar > as > she used to do at Interop, but she's a delightful speaker, once > you > get used to the idea of somebody being a stereotyped New York > Jewish > Mother nagging packets. > = > > This email has been content filtered and > subject to spam filtering. If you consider > this email is unsolicited please forward > the email to [EMAIL PROTECTED] and > request that the sender's domain be > blocked from sending any further emails. > > = > > Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=63814&t=63728 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
RE: L3 Switching Huh???? [7:63728]
>How do you nag a packet? Infact, is it not an oxymoron? How would you feel if you were a packet confronted with a debug log and a demand to explain > >To nag is to continually pester or annoy, yet a packets lifetime is >normally measured in milliseconds, therefore she must be one hell of a >nagger! Trust me. I don't even need to measure Radia; my grandmother had a latency-to-nag beyond the capabilities of measuring equipment. For a different cultural reference, consider the propagation time of a reference implementation Greek ship whose launching is triggered by the application of one milliHelen of face. Histories reveal no latency in such launching once the face is applied, so perhaps this is a lost technology for getting around lightspeed restrictions. > >Ok, it's late, I'll stop. > >Symon Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=63817&t=63728 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
RE: L3 Switching Huh???? [7:63728]
OK, let me try this again. I am trying to figure out the difference between conventional layer 3 routing and layer 3 switching. A little background. I am currently working towards my CCNA (have been for about 3 years). At any rate, everything I read and look at says that switching/bridging is a layer 2 function, routing is a layer 3 function. Either I don't have a good grasp of the OSI model, switching, routing, VLANs or all of the above. The network: Host A 10.1.1.2 MAC 00.AA Host B 10.1.2.2 MAC 00.BB |10.1.1.1 MAC 01.AA 10.1.2.1 MAC 02.BB| switch A---Router-switch B 10.1.1.0/2410.1.2.0/24 This is an ethernet network. Both segments are connected by a traditional router say a 2500. In this instance the router interfaces are subnet A 10.1.1.1, and subnet B 10.1.2.1 For simplicity, assume ARP cache is empty. Host A wishes to ping Host B End user on Host A enters - ping 10.1.2.2 The IP packet places the source address 10.1.1.2 and the destination address 10.1.2.2 into the packet. The IP protocol examines the IP address and based on the IP address determines this is in another subnet. An ARP request goes out for 10.1.1.1 (default gateway) and the MAC address is found. The DLL then places the source MAC address 00.AA and the destination MAC 01.AA into the frame. The frame then goes out the wire to the destination MAC. The router interface sees this frame as destined for itself. It de-encapsulates the frame removing the MAC addresses. The router then examines the IP address, based on the routing table it knows the destination port. The router leaves the same IP source (10.1.1.2) and destination (10.1.2.2) in the packet. The frame is rebuilt with the new MAC address of source 02.BB and destination 00.BB Host B grabs this packet and does it's thing. Now, if I replace the router with a 6509 switch, with routing, how does the process change? Said 6509 would be equipped with a 10/100 card so that the hosts are now directly connected. The router interface is now a virtual interface, there is no physical interface. Which is another question. How does the 6509 determine this virtual address? Am I correct? Inter VLAN communication cannot occur without a router. Switching is based on MAC address. Routing is based on IP address. I believe the term "layer 3 routing" is a marketing term, not scientific or engineering in nature. Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=63857&t=63728 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
RE: L3 Switching Huh???? [7:63728]
If you are using MSFC2/PFC2, the PFC2 (does layer 3 wirespeed 'forwarding' between Vlan) will have a FIB (forwarding information base), which is a copy of the RIB (routing information base). The RIB is built on the MSFC2 (router functions). Even the first packet between Vlan 1 and 2 will be wire speed because the FIB will have an entry saying what is the next hop and the layer 2 header it should use. Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=63861&t=63728 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
RE: L3 Switching Huh???? [7:63728]
That all looks pretty good ... On the MSFC/RSM - do a "show interface": (edited for length) Vlan8 is up, line protocol is up Hardware is Cat6k RP Virtual Ethernet, address is 00d0.d335.6614 Vlan9 is up, line protocol is up Hardware is Cat6k RP Virtual Ethernet, address is 00d0.d335.6614 So ... each 'router interface' has a MAC. The fact that it is the same is irrelevant as they are on different network/logical segments . So the frame comes in with a destination mac of 00d0.d335.6614, and when forwarded will leave with a source mac of 00d0.d335.6614 (same) ... Does that help? Oh - and I think you meant to say "layer 3 switching" is a marketing term, not scientific or engineering in nature. ... you said "layer 3 routing" ... Thanks! TJ [EMAIL PROTECTED] -Original Message- From: DeVoe, Charles (PKI) [mailto:[EMAIL PROTECTED] Sent: Wednesday, February 26, 2003 7:45 AM To: [EMAIL PROTECTED] Subject: RE: L3 Switching Huh [7:63728] OK, let me try this again. I am trying to figure out the difference between conventional layer 3 routing and layer 3 switching. A little background. I am currently working towards my CCNA (have been for about 3 years). At any rate, everything I read and look at says that switching/bridging is a layer 2 function, routing is a layer 3 function. Either I don't have a good grasp of the OSI model, switching, routing, VLANs or all of the above. The network: Host A 10.1.1.2 MAC 00.AA Host B 10.1.2.2 MAC 00.BB |10.1.1.1 MAC 01.AA 10.1.2.1 MAC 02.BB| switch A---Router-switch B 10.1.1.0/2410.1.2.0/24 This is an ethernet network. Both segments are connected by a traditional router say a 2500. In this instance the router interfaces are subnet A 10.1.1.1, and subnet B 10.1.2.1 For simplicity, assume ARP cache is empty. Host A wishes to ping Host B End user on Host A enters - ping 10.1.2.2 The IP packet places the source address 10.1.1.2 and the destination address 10.1.2.2 into the packet. The IP protocol examines the IP address and based on the IP address determines this is in another subnet. An ARP request goes out for 10.1.1.1 (default gateway) and the MAC address is found. The DLL then places the source MAC address 00.AA and the destination MAC 01.AA into the frame. The frame then goes out the wire to the destination MAC. The router interface sees this frame as destined for itself. It de-encapsulates the frame removing the MAC addresses. The router then examines the IP address, based on the routing table it knows the destination port. The router leaves the same IP source (10.1.1.2) and destination (10.1.2.2) in the packet. The frame is rebuilt with the new MAC address of source 02.BB and destination 00.BB Host B grabs this packet and does it's thing. Now, if I replace the router with a 6509 switch, with routing, how does the process change? Said 6509 would be equipped with a 10/100 card so that the hosts are now directly connected. The router interface is now a virtual interface, there is no physical interface. Which is another question. How does the 6509 determine this virtual address? Am I correct? Inter VLAN communication cannot occur without a router. Switching is based on MAC address. Routing is based on IP address. I believe the term "layer 3 routing" is a marketing term, not scientific or engineering in nature. ** The information in this email is confidential and may be legally privileged. Access to this email by anyone other than the intended addressee is unauthorized. If you are not the intended recipient of this message, any review, disclosure, copying, distribution, retention, or any action taken or omitted to be taken in reliance on it is prohibited and may be unlawful. If you are not the intended recipient, please reply to or forward a copy of this message to the sender and delete the message, any attachments, and any copies thereof from your system. ** Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=63869&t=63728 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
RE: L3 Switching Huh???? [7:63728]
Charles, The 6509 switch needs some configuration in the background to create a "virtual router". This "virtual router" has virtual interfaces that would mimic the default gateways IP addresses of the physical 2500 router and therefore pass traffic between the virtual interfaces. The two subnets that you list would be on different VLANs on the switch. It would look like the packets are only going from one interface on the switch to the other and back again, but in reality they are passing through the "virtual router" created on a route processing piece of software. This would be on a multi-layer switch module or similar. Layer 2 = MAC addresses, layer 3 = IP addresses. To get between IP subnets you need a routing function which is either provided by a physical router or a "virtual router" which routes between "virtual LANs" created by software. This is not the definitive answer but hopefully it clears away some of the mud. Cheers, Steve Wilson Network Engineer -Original Message- From: DeVoe, Charles (PKI) [mailto:[EMAIL PROTECTED] Sent: 26 February 2003 12:45 To: [EMAIL PROTECTED] Subject: RE: L3 Switching Huh [7:63728] OK, let me try this again. I am trying to figure out the difference between conventional layer 3 routing and layer 3 switching. A little background. I am currently working towards my CCNA (have been for about 3 years). At any rate, everything I read and look at says that switching/bridging is a layer 2 function, routing is a layer 3 function. Either I don't have a good grasp of the OSI model, switching, routing, VLANs or all of the above. The network: Host A 10.1.1.2 MAC 00.AA Host B 10.1.2.2 MAC 00.BB |10.1.1.1 MAC 01.AA 10.1.2.1 MAC 02.BB| switch A---Router-switch B 10.1.1.0/2410.1.2.0/24 This is an ethernet network. Both segments are connected by a traditional router say a 2500. In this instance the router interfaces are subnet A 10.1.1.1, and subnet B 10.1.2.1 For simplicity, assume ARP cache is empty. Host A wishes to ping Host B End user on Host A enters - ping 10.1.2.2 The IP packet places the source address 10.1.1.2 and the destination address 10.1.2.2 into the packet. The IP protocol examines the IP address and based on the IP address determines this is in another subnet. An ARP request goes out for 10.1.1.1 (default gateway) and the MAC address is found. The DLL then places the source MAC address 00.AA and the destination MAC 01.AA into the frame. The frame then goes out the wire to the destination MAC. The router interface sees this frame as destined for itself. It de-encapsulates the frame removing the MAC addresses. The router then examines the IP address, based on the routing table it knows the destination port. The router leaves the same IP source (10.1.1.2) and destination (10.1.2.2) in the packet. The frame is rebuilt with the new MAC address of source 02.BB and destination 00.BB Host B grabs this packet and does it's thing. Now, if I replace the router with a 6509 switch, with routing, how does the process change? Said 6509 would be equipped with a 10/100 card so that the hosts are now directly connected. The router interface is now a virtual interface, there is no physical interface. Which is another question. How does the 6509 determine this virtual address? Am I correct? Inter VLAN communication cannot occur without a router. Switching is based on MAC address. Routing is based on IP address. I believe the term "layer 3 routing" is a marketing term, not scientific or engineering in nature. Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=63871&t=63728 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
RE: L3 Switching Huh???? [7:63728]
At 12:45 PM + 2/26/03, DeVoe, Charles (PKI) wrote: >OK, let me try this again. I am trying to figure out the difference between >conventional layer 3 routing and layer 3 switching. A little background. I >am currently working towards my CCNA (have been for about 3 years). At any >rate, everything I read and look at says that switching/bridging is a layer >2 function, routing is a layer 3 function. > >Either I don't have a good grasp of the OSI model, switching, routing, VLANs >or all of the above. > No, it's not you. It's that Cisco marketing (in fairness, in response to competitive marketdroids then at Cabletron, Synoptics, etc.) doesn't care to apply a knowledge of this model and likes the industry flavor of "switch fast router slow." Relay destination lookup time simply is not a major problem in router design. At one point, it was, but as router implementers started using faster lookup approaches, the lookup time pales into insignificance compared to things like traffic shaping/policing, accounting, etc. Abraham Lincoln once said, "If you call a horse's tail a leg, how many legs does a horse have?" The audience mumbled "five," and he replied "No. Calling a tail a leg does not make it one." Calling a nonspecific family of routing implementation techniques "L3 switching" doesn't make them anything other than routing. Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=63882&t=63728 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
RE: L3 Switching Huh???? [7:63728]
At 3:18 PM + 2/26/03, Steve Wilson wrote: >Charles, >The 6509 switch needs some configuration in the background to create a >"virtual router". A bit of a heads-up on this term. It's conceptually useful, but be aware that "virtual router" was considered to be an alternate VPN model to RFC 2547, generally promoted by Nortel and Lucent. There have been LOTS of IETF arguments about the term. I didn't make myself popular at one meeting by mentioning "we sure can't define virtual router, but it's nice we have a virtual router redundancy protocol (VRRP is the standards track equivalent to HSRP)." I was severely corrected that I needed to distinguish between "virtual router" and "virtual router," depending on whether the emphasis was on "virtual" or "router." In HSRP/VRRP, the virtual router refers to a single conceptual router seen by hosts, but is actually implemented across multiple platforms. The VPN people thought of virtual routers as multiple independent routing (control and forwarding) logical instances on the same platform. VRF is not quite the same concept, as it assumes more shared knowledge between routing instances than does a VR VPN. Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=63891&t=63728 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
RE: L3 Switching Huh???? [7:63728]
DeVoe, Charles (PKI) wrote: > > OK, let me try this again. I am trying to figure out the > difference between > conventional layer 3 routing and layer 3 switching. A little > background. I > am currently working towards my CCNA (have been for about 3 > years). At any > rate, everything I read and look at says that > switching/bridging is a layer > 2 function, routing is a layer 3 function. > > Either I don't have a good grasp of the OSI model, switching, > routing, VLANs > or all of the above. It sounds like you got it. Don't worry about the terminology so much. You got the concepts and that's what's important. See a few more comments below. > > The network: > > Host A 10.1.1.2 MAC 00.AA > Host B > 10.1.2.2 MAC 00.BB > |10.1.1.1 MAC 01.AA 10.1.2.1 MAC > 02.BB| > switch > A---Router-switch B > 10.1.1.0/2410.1.2.0/24 > > This is an ethernet network. Both segments are connected by a > traditional > router say a 2500. > In this instance the router interfaces are subnet A 10.1.1.1, > and subnet B > 10.1.2.1 > > For simplicity, assume ARP cache is empty. > Host A wishes to ping Host B > End user on Host A enters - ping 10.1.2.2 > The IP packet places the source address 10.1.1.2 and the > destination address > 10.1.2.2 into the packet. > The IP protocol examines the IP address and based on the IP > address > determines this is in another subnet. > An ARP request goes out for 10.1.1.1 (default gateway) and the > MAC address > is found. > The DLL then places the source MAC address 00.AA and the > destination MAC > 01.AA into the frame. > The frame then goes out the wire to the destination MAC. > The router interface sees this frame as destined for itself. It > de-encapsulates the frame removing the MAC addresses. The > router then > examines the IP address, based on the routing table it knows > the destination > port. > The router leaves the same IP source (10.1.1.2) and destination > (10.1.2.2) > in the packet. > The frame is rebuilt with the new MAC address of source 02.BB > and > destination 00.BB > Host B grabs this packet and does it's thing. > > Now, if I replace the router with a 6509 switch, with routing, > how does the > process change? The process is logically the same. I'm not familiar enough with the architecture of the 6509 switch to provide the details, but it looks like others have, so that's good. The important thing is that you understand the traffic flow and what goes in the address fields in the packets. That's great. There are senior network admins that don't get that. Seriously. The CCIE written tests this sort of thing and every so often we get clueless questions about it from people who think they are going to jump right into CCIE as long as we force-feed them the fundamentals. You are doing the right thing by getting down the fundamentals while still studying for CCNA. > Said 6509 would be equipped with a 10/100 card so that the > hosts are now > directly connected. The router interface is now a virtual > interface, there > is no physical interface. Which is another question. How does > the 6509 > determine this virtual address? > > Am I correct? > Inter VLAN communication cannot occur without a router. Yes. > Switching is based on MAC address. > Routing is based on IP address. The word switching is used in a more generic way too and has been for hundreds of years. Switching means forwarding, relaying, routing. Please do not insist that it only happens at L2, despite what the stupid books say. As I have already said, it's not true that it's just a marketing term. It is a good engineering term that the marketing people stole. Train tracks have equipment that switches trains. Telephone equipment switches voice conversations. Electrical devices switch current. An internetworking device switches digital data. For years, Cisco tried to get people to see the same thing that Howard is still trying to get people to see, which is that there are two sets of tasks: one related to learning paths to destinations and one related to forwarding data. For years Cisco called this second path switching. I say this just in the hopes that you will see that even Cisco has used the term switching to mean forwarding, long before L2 switches existed or before marketing people made up the L3 switch term. Priscilla > > I believe the term "layer 3 routing" is a marketing term, not > scientific or > engineering in nature. > > Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=63915&t=63728 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
RE: L3 Switching Huh???? [7:63728]
Evans, TJ (BearingPoint) wrote: > > That all looks pretty good ... > > > On the MSFC/RSM - do a "show interface": (edited for length) > Vlan8 is up, line protocol is up > Hardware is Cat6k RP Virtual Ethernet, address is > 00d0.d335.6614 > > Vlan9 is up, line protocol is up > Hardware is Cat6k RP Virtual Ethernet, address is > 00d0.d335.6614 > So ... each 'router interface' has a MAC. The fact that it is > the same is > irrelevant as they are on different network/logical segments > on different broadcast domains>. > > So the frame comes in with a destination mac of 00d0.d335.6614, > and when > forwarded will leave with a source mac of 00d0.d335.6614 (same) And that's exactly what would happen if you did the inter-VLAN routing on a router too, using subinterfaces for each VLAN/ IP subnet. :-) And, if it were a high-end router, it could do this at wire speed and would have a RIB and FIB, just like someone else described for the 6500. The 7500 router has had that sort of architecture for years, if I'm not mistaken. Howard has given us lots of examples of other high-end routers that have this sort of architecture. Of course, these high-end routers are probably way more expensive than the so-called L3 switch and probably have all sorts of features that you might not need in a campus network. So, we're back to the first answer. The difference between a router and a L3 switch is marketing. Also economics. Sorry, I just had to play devil's advocate. What a shame that Cisco has mangled this so much in their intro training materials. Priscilla > ... > > Does that help? > > Oh - and I think you meant to say "layer 3 switching" is a > marketing term, > not scientific or engineering in nature. ... you said "layer 3 > routing" ... > Thanks! > TJ > [EMAIL PROTECTED] > > > -----Original Message----- > From: DeVoe, Charles (PKI) [mailto:[EMAIL PROTECTED] > Sent: Wednesday, February 26, 2003 7:45 AM > To: [EMAIL PROTECTED] > Subject: RE: L3 Switching Huh [7:63728] > > OK, let me try this again. I am trying to figure out the > difference between > conventional layer 3 routing and layer 3 switching. A little > background. I > am currently working towards my CCNA (have been for about 3 > years). At any > rate, everything I read and look at says that > switching/bridging is a layer > 2 function, routing is a layer 3 function. > > Either I don't have a good grasp of the OSI model, switching, > routing, VLANs > or all of the above. > > The network: > > Host A 10.1.1.2 MAC 00.AA > Host B > 10.1.2.2 MAC 00.BB > |10.1.1.1 MAC 01.AA 10.1.2.1 MAC > 02.BB| > switch > A---Router-switch B > 10.1.1.0/2410.1.2.0/24 > > This is an ethernet network. Both segments are connected by a > traditional > router say a 2500. > In this instance the router interfaces are subnet A 10.1.1.1, > and subnet B > 10.1.2.1 > > For simplicity, assume ARP cache is empty. > Host A wishes to ping Host B > End user on Host A enters - ping 10.1.2.2 > The IP packet places the source address 10.1.1.2 and the > destination address > 10.1.2.2 into the packet. > The IP protocol examines the IP address and based on the IP > address > determines this is in another subnet. > An ARP request goes out for 10.1.1.1 (default gateway) and the > MAC address > is found. > The DLL then places the source MAC address 00.AA and the > destination MAC > 01.AA into the frame. > The frame then goes out the wire to the destination MAC. > The router interface sees this frame as destined for itself. It > de-encapsulates the frame removing the MAC addresses. The > router then > examines the IP address, based on the routing table it knows > the destination > port. > The router leaves the same IP source (10.1.1.2) and destination > (10.1.2.2) > in the packet. > The frame is rebuilt with the new MAC address of source 02.BB > and > destination 00.BB > Host B grabs this packet and does it's thing. > > Now, if I replace the router with a 6509 switch, with routing, > how does the > process change? > Said 6509 would be equipped with a 10/100 card so that the > hosts are now > directly connected. The router interface is now a virtual > interface, there > is no physical interface. Which is another question. How does > the 6509 > determine this virtual address? > > Am I correct? > Inter VLAN communication cannot occur without a router. > Switching is based on MAC ad
RE: L3 Switching Huh???? [7:63728]
A >And that's exactly what would happen if you did the inter-VLAN routing on a >router too, using subinterfaces for each VLAN/ IP subnet. :-) > >And, if it were a high-end router, it could do this at wire speed and would >have a RIB and FIB, just like someone else described for the 6500. The 7500 >router has had that sort of architecture for years, if I'm not mistaken. >Howard has given us lots of examples of other high-end routers that have >this sort of architecture. Of course, these high-end routers are probably >way more expensive than the so-called L3 switch and probably have all sorts >of features that you might not need in a campus network. Last I check, extreme make some pretty cheap bridges with integrated routing :) Naturally, to get a bunch of packet processing without mortgaging forwarding capacity, you'll end up spending more bucks. Howard's point about the relevance of wire speed routing in the enterprise is dead on though - most folks don't need it and wouldn't make use of it even if they had it. >So, we're back to the first answer. The difference between a router and a L3 >switch is marketing. Also economics. > >Sorry, I just had to play devil's advocate. What a shame that Cisco has >mangled this so much in their intro training materials. > >Priscilla > > > ... > > > > Does that help? > > > > Oh - and I think you meant to say "layer 3 switching" is a > > marketing term, > > not scientific or engineering in nature. ... you said "layer 3 > > routing" ... > > Thanks! > > TJ > > [EMAIL PROTECTED] > > > > > > -Original Message- > > From: DeVoe, Charles (PKI) [mailto:[EMAIL PROTECTED] > > Sent: Wednesday, February 26, 2003 7:45 AM > > To: [EMAIL PROTECTED] > > Subject: RE: L3 Switching Huh [7:63728] > > > > OK, let me try this again. I am trying to figure out the > > difference between > > conventional layer 3 routing and layer 3 switching. A little > > background. I > > am currently working towards my CCNA (have been for about 3 > > years). At any > > rate, everything I read and look at says that > > switching/bridging is a layer > > 2 function, routing is a layer 3 function. > > > > Either I don't have a good grasp of the OSI model, switching, > > routing, VLANs > > or all of the above. > > > > The network: > > > > Host A 10.1.1.2 MAC 00.AA > > Host B > > 10.1.2.2 MAC 00.BB > > |10.1.1.1 MAC 01.AA 10.1.2.1 MAC > > 02.BB| > > switch > > A---Router-switch B > > 10.1.1.0/2410.1.2.0/24 > > > > This is an ethernet network. Both segments are connected by a > > traditional > > router say a 2500. > > In this instance the router interfaces are subnet A 10.1.1.1, > > and subnet B > > 10.1.2.1 > > > > For simplicity, assume ARP cache is empty. > > Host A wishes to ping Host B > > End user on Host A enters - ping 10.1.2.2 > > The IP packet places the source address 10.1.1.2 and the > > destination address > > 10.1.2.2 into the packet. > > The IP protocol examines the IP address and based on the IP > > address > > determines this is in another subnet. > > An ARP request goes out for 10.1.1.1 (default gateway) and the > > MAC address > > is found. > > The DLL then places the source MAC address 00.AA and the > > destination MAC > > 01.AA into the frame. > > The frame then goes out the wire to the destination MAC. > > The router interface sees this frame as destined for itself. It > > de-encapsulates the frame removing the MAC addresses. The > > router then > > examines the IP address, based on the routing table it knows > > the destination > > port. > > The router leaves the same IP source (10.1.1.2) and destination > > (10.1.2.2) > > in the packet. > > The frame is rebuilt with the new MAC address of source 02.BB > > and > > destination 00.BB > > Host B grabs this packet and does it's thing. > > > > Now, if I replace the router with a 6509 switch, with routing, > > how does the > > process change? > > Said 6509 would be equipped with a 10/100 card so that the > > hosts are now > > directly connected. The router interface is now a virtual > > interface, there > > is no physical interface. Which is another question. How does > > the 6509 > > determine this virtual address? > > > > Am I correct?
RE: L3 Switching Huh???? [7:63728]
Thanks for the definition assistance. The problem with trying to assist in a forum such as this is that if you try to simplify an answer you end up with an answer that is too simple. All I was trying to get across was my way of looking at the difference between a physically separate routing device working at layer3 between subnets and a chassis like a 6509 which can have individual blades perform the functions without the limitation of wires between the physical interfaces. The "wires" are still there, they are just created in software in the chassis. Cheers, Steve Wilson Network Engineer -Original Message- From: Howard C. Berkowitz [mailto:[EMAIL PROTECTED] Sent: 26 February 2003 18:27 To: [EMAIL PROTECTED] Subject: RE: L3 Switching Huh???? [7:63728] At 3:18 PM + 2/26/03, Steve Wilson wrote: >Charles, >The 6509 switch needs some configuration in the background to create a >"virtual router". A bit of a heads-up on this term. It's conceptually useful, but be aware that "virtual router" was considered to be an alternate VPN model to RFC 2547, generally promoted by Nortel and Lucent. There have been LOTS of IETF arguments about the term. I didn't make myself popular at one meeting by mentioning "we sure can't define virtual router, but it's nice we have a virtual router redundancy protocol (VRRP is the standards track equivalent to HSRP)." I was severely corrected that I needed to distinguish between "virtual router" and "virtual router," depending on whether the emphasis was on "virtual" or "router." In HSRP/VRRP, the virtual router refers to a single conceptual router seen by hosts, but is actually implemented across multiple platforms. The VPN people thought of virtual routers as multiple independent routing (control and forwarding) logical instances on the same platform. VRF is not quite the same concept, as it assumes more shared knowledge between routing instances than does a VR VPN. Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=63954&t=63728 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
RE: L3 Switching Huh???? [7:63728]
At 9:11 AM + 2/27/03, Steve Wilson wrote: >Thanks for the definition assistance. >The problem with trying to assist in a forum such as this is that if you try >to simplify an answer you end up with an answer that is too simple. All I >was trying to get across was my way of looking at the difference between a >physically separate routing device working at layer3 between subnets and a >chassis like a 6509 which can have individual blades perform the functions >without the limitation of wires between the physical interfaces. The "wires" >are still there, they are just created in software in the chassis. > >Cheers, >Steve Wilson >Network Engineer Definite cheers in return. As you point out, it's easy to oversimplify--one of the reasons I avoid the L3 switching terminology. It's routing--there are just a wide range of router product design techniques, with different optimizations. Some of these optimizations are for maximum forwarding speed, others are for cost, others for QoS power, etc. To me, a virtual router implies there are at least two distinct control-and-forwarding entities (1 RIB and 1 FIB minimum each). I think this started with a fairly simple CCNA/CCNP level question--I've lost track at this point. My strong opinion is that for the purpose of initial understanding, trying to deal with L3 switching as a significantly different technique is totally confusing for people learning the basics. For them, L3 switching = routing, and then certain speeds, feeds, and feature sets. Choosing those speeds/feeds/feature sets is really a higher skill set for specific network design. The 6500 architecture (as is, for that matter, the 7500, 1, 12000...) involves a single active control instance and one or more physical forwarding instances in the same chassis, which is slightly different than either of my VR definitions. MLS gets even more confusing when one realizes that on a 5500, the control engine running the routing protocols can be on a completely external box, but the FIB is in a L3 forwarding board in the chassis with multiple L2 blades. 7500s and up actually can have multiple physical L3 forwarding instances. Without even getting into the researchy area of active multiprocessing in the control plane, things are very blurred on how to consider the 6509 by your definition above. I tend to think about it as a set of blades interconnected by a network, which just happens to be in the fabric. In other words, there isn't a huge difference between wires between physical interfaces and fabric, as long as the "wires" are fast enough. There are off-the-shelf optoelectronic fabric chipsets that run at OC-48 and OC-192, but aren't limited to 10 Gbps because they aren't limited to parallel interfacing. In other words, we get very blurred about whether the "box" is still more or less monolithic, or really should be considered an enclosure for a small Storage Area Network interconnecting the blades. I rather prefer the latter. Howard > >-Original Message- >From: Howard C. Berkowitz [mailto:[EMAIL PROTECTED] >Sent: 26 February 2003 18:27 >To: [EMAIL PROTECTED] >Subject: RE: L3 Switching Huh [7:63728] > >At 3:18 PM + 2/26/03, Steve Wilson wrote: >>Charles, >>The 6509 switch needs some configuration in the background to create a >>"virtual router". > > >A bit of a heads-up on this term. It's conceptually useful, but be >aware that "virtual router" was considered to be an alternate VPN >model to RFC 2547, generally promoted by Nortel and Lucent. > >There have been LOTS of IETF arguments about the term. I didn't make >myself popular at one meeting by mentioning "we sure can't define >virtual router, but it's nice we have a virtual router redundancy >protocol (VRRP is the standards track equivalent to HSRP)." > >I was severely corrected that I needed to distinguish between >"virtual router" and "virtual router," depending on whether the >emphasis was on "virtual" or "router." In HSRP/VRRP, the virtual >router refers to a single conceptual router seen by hosts, but is >actually implemented across multiple platforms. > >The VPN people thought of virtual routers as multiple independent >routing (control and forwarding) logical instances on the same >platform. VRF is not quite the same concept, as it assumes more >shared knowledge between routing instances than does a VR VPN. Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=63966&t=63728 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
Radia, Re: L3 Switching Huh???? [7:63728]
>Howard C. Berkowitz wrote: > >> >Strongly recommend her book. The lady has a lot of style. >> > >> >> I don't remember if she's still doing a protocol design seminar >> as >> she used to do at Interop, but she's a delightful speaker, once >> you >> get used to the idea of somebody being a stereotyped New York >> Jewish >> Mother nagging packets. > >I don't think Radia Perlman fits any stereotype, actually. She is a unique >entity. I found out recently that her name is pronounced like radiate and >radio, which I thought was perfect. She radiates intelligence, humor, >cynicism, and earth-mother goddess. (Well, and maybe Jewish mother too! ;-) This is too funny. As I read the post that mentions Radia I was wondering how her name was pronounced. I always thought it was "rah dee uh", but I had an instructor who said it was "ray dee uh". I'd never known which was actually correct. That's similar to Paul's last name. I never knew how to pronounce Borghese until I heard it on his voice mail. :-) Hmm... it's also similar to Peter Van Oene's name. I think Peter and I have had this discussion before.Or how about Mr. Luhrooh? John Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=63808&t=63728 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
