Re: Layer 3 switch ? [7:38358]
Great answer, Howard. We like to think of a router as having a simple table like this: prefix next-hop prefix next-hop prefix next-hop But, from my limited knowledge, I don't believe any modern day router really stores "address lookup" data in this way. They don't use trees any more either. In recent reading, I found information about multbit tries (not a typo). I was just surfing, but I think you can find information about tries at Cisco's site too. CEF uses a trie also. Also, from my surfing I have discovered that computer science departments these days have computer networking classes in "Switching Systems." These classes cover the processing required of any network switch, whether it's switching cells, L2 frames, L3 packets, etc. This course at Washington University in St. Louis has a good Web site: http://boushi.arl.wustl.edu/~jst/cs/577/ Well, it is a Friday night in March. So instead of looking at more university computer science Web sites, I think I will now go watch some college basketball! Priscilla At 07:50 PM 3/15/02, Howard C. Berkowitz wrote: >At 6:44 PM -0500 3/15/02, mlh wrote: > >no, IRB is a technique integrating routing and bridging. > >but switching routers use hardware switching technique > >which based on layer 3 address not layer 2 address. > >this is one of the differences between router switches > >and switching routers. > >it's my point, pls correct it. > > >Again speaking from router design experience, the difference between >layer 3, label, and layer 2 forwarding is less profound than one >might think. > >The frame arrives on the ingress port and gets buffered and >validated. I'll ignore VLANs. Assuming it were an Ethernet frame, the >forwarder would extract the first 6 bytes. If it were an ordinary >packet, it would extract the destination IP address (Bytes 12-15 >following the LLC field if one is present). If it's MPLS, it extracts >the 32 bits following the data link header. > >MAC addresses get looked up directly, possibly in a CAM. Admittedly, >that's probably faster than radix tree lookup, discussed next, but >destination lookup time is rarely the limiting factor in >router/switch performance. It's pretty much a solved problem. The >size of routing/forwarding tables is much more limited by the ability >of the routing protocols to reconverge in a reasonable time than the >time of search. FIBs generally have a constant lookuo time. > >Some masking is applied to the IP and MPLS addresses, and then the >prefix or label is usually looked up in some sort of radix tree in >static RAM. > >Any of these searches pop up the destination port (not address) if >one is known, plus other information about processing (e.g., QoS). >Statistics are incremented, error check fields are checked, and the >packet/frame goes to the fabric. Crossbar fabrics usually are >nonblocking, while shared busses may need buffering. > >Bottom line: layer 2 switch, layer 3 switch, MPLS switch, router, >etc., are more marketing than architectural distinctions. There are >differences between MPLS Label Edge Routers and Label Switched >Routers, before we get into the GMPLS non-packet forwarders (e.g., >wavelength switches). > >Remember what Cisco calls something in its literature, but don't >obsess over arbitrarily fitting one box into a category. > > > > >- Original Message - > >From: "Chuck" > >To: > >Sent: Friday, March 15, 2002 11:24 AM > >Subject: Re: Layer 3 switch ? [7:38358] > > > > > >> so if I enable IRB on my 2501, I now have a layer 3 switch? ;-> > >> > >> > >> ""mlh"" wrote in message > >> [EMAIL PROTECTED]">news:[EMAIL PROTECTED]... > >> > According to Clark's Cisco LAN Switching(page 452 ), > >> > layer 3 switching techniques can be grouped > >> > into two categories: > >> > Routing switches > >> > Switching routers > >> > > >> > mlh > >> > > >> > - Original Message - > >> > From: "Larry Letterman" > >> > To: > >> > Sent: Friday, March 15, 2002 2:48 AM > >> > Subject: RE: Layer 3 switch ? [7:38358] > >> > > >> > > >> > > A true router, 2621/3640/7200, is not usually considered > >> > > a L3 switch. A 6500 with an MSFC module installed can be > >> > > is a L3 switch and will perform L2/L3 routing and switching. > >> > > > >> > > A 6500 without the MSFC module is just a large high speed switch, > >> > &
Re: Layer 3 switch ? [7:38358]
At 6:44 PM -0500 3/15/02, mlh wrote: >no, IRB is a technique integrating routing and bridging. >but switching routers use hardware switching technique >which based on layer 3 address not layer 2 address. >this is one of the differences between router switches >and switching routers. >it's my point, pls correct it. Again speaking from router design experience, the difference between layer 3, label, and layer 2 forwarding is less profound than one might think. The frame arrives on the ingress port and gets buffered and validated. I'll ignore VLANs. Assuming it were an Ethernet frame, the forwarder would extract the first 6 bytes. If it were an ordinary packet, it would extract the destination IP address (Bytes 12-15 following the LLC field if one is present). If it's MPLS, it extracts the 32 bits following the data link header. MAC addresses get looked up directly, possibly in a CAM. Admittedly, that's probably faster than radix tree lookup, discussed next, but destination lookup time is rarely the limiting factor in router/switch performance. It's pretty much a solved problem. The size of routing/forwarding tables is much more limited by the ability of the routing protocols to reconverge in a reasonable time than the time of search. FIBs generally have a constant lookuo time. Some masking is applied to the IP and MPLS addresses, and then the prefix or label is usually looked up in some sort of radix tree in static RAM. Any of these searches pop up the destination port (not address) if one is known, plus other information about processing (e.g., QoS). Statistics are incremented, error check fields are checked, and the packet/frame goes to the fabric. Crossbar fabrics usually are nonblocking, while shared busses may need buffering. Bottom line: layer 2 switch, layer 3 switch, MPLS switch, router, etc., are more marketing than architectural distinctions. There are differences between MPLS Label Edge Routers and Label Switched Routers, before we get into the GMPLS non-packet forwarders (e.g., wavelength switches). Remember what Cisco calls something in its literature, but don't obsess over arbitrarily fitting one box into a category. > >- Original Message - >From: "Chuck" >To: >Sent: Friday, March 15, 2002 11:24 AM >Subject: Re: Layer 3 switch ? [7:38358] > > >> so if I enable IRB on my 2501, I now have a layer 3 switch? ;-> >> >> >> ""mlh"" wrote in message >> [EMAIL PROTECTED]">news:[EMAIL PROTECTED]... >> > According to Clark's Cisco LAN Switching(page 452 ), >> > layer 3 switching techniques can be grouped >> > into two categories: >> > Routing switches >> > Switching routers >> > >> > mlh >> > >> > - Original Message - >> > From: "Larry Letterman" >> > To: >> > Sent: Friday, March 15, 2002 2:48 AM >> > Subject: RE: Layer 3 switch ? [7:38358] >> > >> > >> > > A true router, 2621/3640/7200, is not usually considered >> > > a L3 switch. A 6500 with an MSFC module installed can be >> > > is a L3 switch and will perform L2/L3 routing and switching. >> > > >> > > A 6500 without the MSFC module is just a large high speed switch, >> > > capable of only L2 switching. >> > > >> > > A layer 3 switch usually routes the first packet in the flow of data >> > > and then switches the rest in the switching hardware. This is why L3 >> > > routing/switching is quite a bit faster. A traditional router will use >> > > IOS software to determine routes and the switch each packet between >the >> > > interfaces in the router. >> > > >> > > >> > > Larry Letterman >> > > Cisco Systems >> > > [EMAIL PROTECTED] >> > > >> > > >> > > -Original Message- >> > > From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of >> > > John Green >> > > Sent: Thursday, March 14, 2002 10:50 PM >> > > To: [EMAIL PROTECTED] > > > > Subject: Layer 3 switch ? [7:38358] >> > > >> > > >> > > Is it ok to refer to a "router" as a Layer 3 switch ? >> > > >> > > cisco 6500 was referred to as a Layer 3 switch. >> > > >> > > question: does it(6500) have routing capabilities ? >> > > - >> > > >> > > to connect to different vlans one needs a router. >> > > right ?
Re: Layer 3 switch ? [7:38358]
no, IRB is a technique integrating routing and bridging. but switching routers use hardware switching technique which based on layer 3 address not layer 2 address. this is one of the differences between router switches and switching routers. it's my point, pls correct it. - Original Message - From: "Chuck" To: Sent: Friday, March 15, 2002 11:24 AM Subject: Re: Layer 3 switch ? [7:38358] > so if I enable IRB on my 2501, I now have a layer 3 switch? ;-> > > > ""mlh"" wrote in message > [EMAIL PROTECTED]">news:[EMAIL PROTECTED]... > > According to Clark's Cisco LAN Switching(page 452 ), > > layer 3 switching techniques can be grouped > > into two categories: > > Routing switches > > Switching routers > > > > mlh > > > > ----- Original Message - > > From: "Larry Letterman" > > To: > > Sent: Friday, March 15, 2002 2:48 AM > > Subject: RE: Layer 3 switch ? [7:38358] > > > > > > > A true router, 2621/3640/7200, is not usually considered > > > a L3 switch. A 6500 with an MSFC module installed can be > > > is a L3 switch and will perform L2/L3 routing and switching. > > > > > > A 6500 without the MSFC module is just a large high speed switch, > > > capable of only L2 switching. > > > > > > A layer 3 switch usually routes the first packet in the flow of data > > > and then switches the rest in the switching hardware. This is why L3 > > > routing/switching is quite a bit faster. A traditional router will use > > > IOS software to determine routes and the switch each packet between the > > > interfaces in the router. > > > > > > > > > Larry Letterman > > > Cisco Systems > > > [EMAIL PROTECTED] > > > > > > > > > -Original Message- > > > From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of > > > John Green > > > Sent: Thursday, March 14, 2002 10:50 PM > > > To: [EMAIL PROTECTED] > > > Subject: Layer 3 switch ? [7:38358] > > > > > > > > > Is it ok to refer to a "router" as a Layer 3 switch ? > > > > > > cisco 6500 was referred to as a Layer 3 switch. > > > > > > question: does it(6500) have routing capabilities ? > > > - > > > > > > to connect to different vlans one needs a router. > > > right ?? (as shown below) > > > switchA ROUTER---switchB > > > > > > but say some nodes connected to switchB are on the > > > vlan of switchA. so now to connect switchA and switchB > > > can router be ok ? > > > -- > > > > > > __ > > > Do You Yahoo!? > > > Yahoo! Sports - live college hoops coverage > > > http://sports.yahoo.com/ Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=38493&t=38358 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
Re: Layer 3 switch ? [7:38358]
so if I enable IRB on my 2501, I now have a layer 3 switch? ;-> ""mlh"" wrote in message [EMAIL PROTECTED]">news:[EMAIL PROTECTED]... > According to Clark's Cisco LAN Switching(page 452 ), > layer 3 switching techniques can be grouped > into two categories: > Routing switches > Switching routers > > mlh > > - Original Message - > From: "Larry Letterman" > To: > Sent: Friday, March 15, 2002 2:48 AM > Subject: RE: Layer 3 switch ? [7:38358] > > > > A true router, 2621/3640/7200, is not usually considered > > a L3 switch. A 6500 with an MSFC module installed can be > > is a L3 switch and will perform L2/L3 routing and switching. > > > > A 6500 without the MSFC module is just a large high speed switch, > > capable of only L2 switching. > > > > A layer 3 switch usually routes the first packet in the flow of data > > and then switches the rest in the switching hardware. This is why L3 > > routing/switching is quite a bit faster. A traditional router will use > > IOS software to determine routes and the switch each packet between the > > interfaces in the router. > > > > > > Larry Letterman > > Cisco Systems > > [EMAIL PROTECTED] > > > > > > -Original Message- > > From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of > > John Green > > Sent: Thursday, March 14, 2002 10:50 PM > > To: [EMAIL PROTECTED] > > Subject: Layer 3 switch ? [7:38358] > > > > > > Is it ok to refer to a "router" as a Layer 3 switch ? > > > > cisco 6500 was referred to as a Layer 3 switch. > > > > question: does it(6500) have routing capabilities ? > > - > > > > to connect to different vlans one needs a router. > > right ?? (as shown below) > > switchA ROUTER---switchB > > > > but say some nodes connected to switchB are on the > > vlan of switchA. so now to connect switchA and switchB > > can router be ok ? > > -- > > > > __ > > Do You Yahoo!? > > Yahoo! Sports - live college hoops coverage > > http://sports.yahoo.com/ Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=38418&t=38358 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
RE: Layer 3 switch ? [7:38358]
I expected I would get plenty of corrections to my post, like Howards and others any and all corrections are fully welcome...:) Larry Letterman Cisco Systems [EMAIL PROTECTED] -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of mlh Sent: Friday, March 15, 2002 7:56 AM To: [EMAIL PROTECTED] Subject: Re: Layer 3 switch ? [7:38358] According to Clark's Cisco LAN Switching(page 452 ), layer 3 switching techniques can be grouped into two categories: Routing switches Switching routers mlh - Original Message - From: "Larry Letterman" To: Sent: Friday, March 15, 2002 2:48 AM Subject: RE: Layer 3 switch ? [7:38358] > A true router, 2621/3640/7200, is not usually considered > a L3 switch. A 6500 with an MSFC module installed can be > is a L3 switch and will perform L2/L3 routing and switching. > > A 6500 without the MSFC module is just a large high speed switch, > capable of only L2 switching. > > A layer 3 switch usually routes the first packet in the flow of data > and then switches the rest in the switching hardware. This is why L3 > routing/switching is quite a bit faster. A traditional router will use > IOS software to determine routes and the switch each packet between the > interfaces in the router. > > > Larry Letterman > Cisco Systems > [EMAIL PROTECTED] > > > -Original Message- > From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of > John Green > Sent: Thursday, March 14, 2002 10:50 PM > To: [EMAIL PROTECTED] > Subject: Layer 3 switch ? [7:38358] > > > Is it ok to refer to a "router" as a Layer 3 switch ? > > cisco 6500 was referred to as a Layer 3 switch. > > question: does it(6500) have routing capabilities ? > - > > to connect to different vlans one needs a router. > right ?? (as shown below) > switchA ROUTER---switchB > > but say some nodes connected to switchB are on the > vlan of switchA. so now to connect switchA and switchB > can router be ok ? > -- > > __ > Do You Yahoo!? > Yahoo! Sports - live college hoops coverage > http://sports.yahoo.com/ Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=38430&t=38358 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
Re: Layer 3 switch ? [7:38358]
According to Clark's Cisco LAN Switching(page 452 ), layer 3 switching techniques can be grouped into two categories: Routing switches Switching routers mlh - Original Message - From: "Larry Letterman" To: Sent: Friday, March 15, 2002 2:48 AM Subject: RE: Layer 3 switch ? [7:38358] > A true router, 2621/3640/7200, is not usually considered > a L3 switch. A 6500 with an MSFC module installed can be > is a L3 switch and will perform L2/L3 routing and switching. > > A 6500 without the MSFC module is just a large high speed switch, > capable of only L2 switching. > > A layer 3 switch usually routes the first packet in the flow of data > and then switches the rest in the switching hardware. This is why L3 > routing/switching is quite a bit faster. A traditional router will use > IOS software to determine routes and the switch each packet between the > interfaces in the router. > > > Larry Letterman > Cisco Systems > [EMAIL PROTECTED] > > > -Original Message- > From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of > John Green > Sent: Thursday, March 14, 2002 10:50 PM > To: [EMAIL PROTECTED] > Subject: Layer 3 switch ? [7:38358] > > > Is it ok to refer to a "router" as a Layer 3 switch ? > > cisco 6500 was referred to as a Layer 3 switch. > > question: does it(6500) have routing capabilities ? > - > > to connect to different vlans one needs a router. > right ?? (as shown below) > switchA ROUTER---switchB > > but say some nodes connected to switchB are on the > vlan of switchA. so now to connect switchA and switchB > can router be ok ? > -- > > __ > Do You Yahoo!? > Yahoo! Sports - live college hoops coverage > http://sports.yahoo.com/ Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=38407&t=38358 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
Re: Layer 3 switch ? [7:38358]
It is far more accurate to describe a layer 3 switch as a router. A router consists of a control function and forwarding function. In many modern routers, there is a single control processor and multiple forwarding engines. Of the carrier-class routers where I am familiar with the internal design, there simply isn't as much of a distinction between layer 3 and layer 2 forwarding as much marketing material makes it out to be. The ingress forwarder looks up the destination address (and other things) in an appropriate hardware-assisted table, which, among other things, returns the desired output port. A header telling the fabric what to do with the packet or frame (e.g., send it to a port, multicast it to several ports) is prepended to the packet or frame, which is then handed off to the fabric. Most of the intelligence is on the input forwarder. The idea of physically separating the control and forwarding elements began with the AGS and autonomous switching, and has continued to develop. There is an IETF working group called FORCES that is looking at general protocols and architectures for such things as external control engines (i.e., external routers telling a switch how to forward). >Hi, > >The term "layer 3 switch" is used to describe a switch >that has routing capabilities. In the 6509, routing is >handled by the MSFC daughtercard on the Sup module. > >If you do a 'show module' the MSFC is in slot 15 >and/or 16. If you do a 'session 15' you >reverse-telnet/console into the router module from the >switch prompt if using Hybrid IOS. > >You don't need to route on the 6500 with the MSFC, you >could use a external router as well if you want but >the 6500+MSFC combo is faster. > >--- John Green wrote: >> Is it ok to refer to a "router" as a Layer 3 switch >> ? >> >> cisco 6500 was referred to as a Layer 3 switch. >> >> question: does it(6500) have routing capabilities ? >> >- >> >> to connect to different vlans one needs a router. >> right ?? (as shown below) >> switchA ROUTER---switchB >> >> but say some nodes connected to switchB are on the >> vlan of switchA. so now to connect switchA and >> switchB >> can router be ok ? > > > -- "What Problem are you trying to solve?" ***send Cisco questions to the list, so all can benefit -- not directly to me*** Howard C. Berkowitz [EMAIL PROTECTED] Chief Technology Officer, GettLab/Gett Communications http://www.gettlabs.com Technical Director, CertificationZone.com http://www.certificationzone.com "retired" Certified Cisco Systems Instructor (CID) #93005 Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=38389&t=38358 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
RE: Layer 3 switch ? [7:38358]
>A true router, 2621/3640/7200, is not usually considered >a L3 switch. A 6500 with an MSFC module installed can be >is a L3 switch and will perform L2/L3 routing and switching. > >A 6500 without the MSFC module is just a large high speed switch, >capable of only L2 switching. > >A layer 3 switch usually routes the first packet in the flow of data >and then switches the rest in the switching hardware. This is why L3 >routing/switching is quite a bit faster. A traditional router will use >IOS software to determine routes and the switch each packet between the >interfaces in the router. This is a legitimate argument for process and fast switching,perhaps for central flow switching, and marginally for optimum switching. I would argue it no longer holds in any form of distributed switching. VIPs, 12000 forwarders, etc. are not IOS software engines. > > >Larry Letterman >Cisco Systems >[EMAIL PROTECTED] -- "What Problem are you trying to solve?" ***send Cisco questions to the list, so all can benefit -- not directly to me*** Howard C. Berkowitz [EMAIL PROTECTED] Chief Technology Officer, GettLab/Gett Communications http://www.gettlabs.com Technical Director, CertificationZone.com http://www.certificationzone.com "retired" Certified Cisco Systems Instructor (CID) #93005 Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=38390&t=38358 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
RE: Layer 3 switch ? [7:38358]
A true router, 2621/3640/7200, is not usually considered a L3 switch. A 6500 with an MSFC module installed can be is a L3 switch and will perform L2/L3 routing and switching. A 6500 without the MSFC module is just a large high speed switch, capable of only L2 switching. A layer 3 switch usually routes the first packet in the flow of data and then switches the rest in the switching hardware. This is why L3 routing/switching is quite a bit faster. A traditional router will use IOS software to determine routes and the switch each packet between the interfaces in the router. Larry Letterman Cisco Systems [EMAIL PROTECTED] -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of John Green Sent: Thursday, March 14, 2002 10:50 PM To: [EMAIL PROTECTED] Subject: Layer 3 switch ? [7:38358] Is it ok to refer to a "router" as a Layer 3 switch ? cisco 6500 was referred to as a Layer 3 switch. question: does it(6500) have routing capabilities ? - to connect to different vlans one needs a router. right ?? (as shown below) switchA ROUTER---switchB but say some nodes connected to switchB are on the vlan of switchA. so now to connect switchA and switchB can router be ok ? -- __ Do You Yahoo!? Yahoo! Sports - live college hoops coverage http://sports.yahoo.com/ Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=38364&t=38358 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
Re: Layer 3 switch ? [7:38358]
Hi, The term "layer 3 switch" is used to describe a switch that has routing capabilities. In the 6509, routing is handled by the MSFC daughtercard on the Sup module. If you do a 'show module' the MSFC is in slot 15 and/or 16. If you do a 'session 15' you reverse-telnet/console into the router module from the switch prompt if using Hybrid IOS. You don't need to route on the 6500 with the MSFC, you could use a external router as well if you want but the 6500+MSFC combo is faster. --- John Green wrote: > Is it ok to refer to a "router" as a Layer 3 switch > ? > > cisco 6500 was referred to as a Layer 3 switch. > > question: does it(6500) have routing capabilities ? > - > > to connect to different vlans one needs a router. > right ?? (as shown below) > switchA ROUTER---switchB > > but say some nodes connected to switchB are on the > vlan of switchA. so now to connect switchA and > switchB > can router be ok ? > __ Do You Yahoo!? Yahoo! Sports - live college hoops coverage http://sports.yahoo.com/ Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=38361&t=38358 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
Layer 3 switch ? [7:38358]
Is it ok to refer to a "router" as a Layer 3 switch ? cisco 6500 was referred to as a Layer 3 switch. question: does it(6500) have routing capabilities ? - to connect to different vlans one needs a router. right ?? (as shown below) switchA ROUTER---switchB but say some nodes connected to switchB are on the vlan of switchA. so now to connect switchA and switchB can router be ok ? -- __ Do You Yahoo!? Yahoo! Sports - live college hoops coverage http://sports.yahoo.com/ Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=38358&t=38358 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
