Re: Equal cost switching
At 04:07 PM 2/19/01, Howard C. Berkowitz wrote: >At 11:21 AM 2/19/2001 -0800, Priscilla Oppenheimer wrote: >>At 08:14 AM 2/19/01, AndyD wrote: >> >> >> >It looks like you need to go to >> >layer 3 switching to do any load balancing other than this. And >> >etherchannel is another option for aggregating bandwidth. But someone said >> >with etherchannel using 4 full duplex 100 mbp ports will not give 800 mbps >> >of throughput? I always thought that in theory that was the case?? >> >>It's "statistical" load balancing, according to Cisco. The operation that >>determines which link in a Fast EtherChannel to use is quite bizarre, and >>does not provide precise load balancing. It provides load sharing. Think of >>it like a complex highway system. Adding new highways distributes the load, >>but it doesn't usually balance the load very precisely. > >Are you saying it should provide precise load balancing? Definitely not. I think the implementation is ingenious and well-suited to the problem. I probably should have said that instead of bizarre (though the XOR business is kind of strange.) Priscilla > That would seem to add a scary amount >of knowledge that the FEC interface would need to know -- RMON traffic >statistics or the like to >figure out how to distribute flows. Intuitively, the cost of adding that >intelligence would exceed, >by far, the cost of throwing more bandwidth at the problem. > >Recovery after failure would take longer as well, IMHO. > > >>The division of traffic across a Fast EtherChannel is based on >>source/destination pairs, which is usually not very balanced. There are >>usually some big talkers and receivers. The Ethernet Bundling Controller >>(EBC) performs an X-OR operation on the last two bits of the source MAC >>address and the destination MAC address. This operation yields one of four >>results: (0 0), (0 1), (1 0), or (1 1). Each of these values points to a >>link in the Fast EtherChannel bundle. >> >>Priscilla >> >> > Since >> >the data is transmitted on different wire pairs, if the sender and receiver >> >transmit at the same time, why isn't 800 mbps possible >> > > >_ >FAQ, list archives, and subscription info: >http://www.groupstudy.com/list/cisco.html >Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] Priscilla Oppenheimer http://www.priscilla.com _ FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
Re: Equal cost switching
At 11:21 AM 2/19/2001 -0800, Priscilla Oppenheimer wrote: At 08:14 AM 2/19/01, AndyD wrote: >It looks like you need to go to >layer 3 switching to do any load balancing other than this. And >etherchannel is another option for aggregating bandwidth. But someone said >with etherchannel using 4 full duplex 100 mbp ports will not give 800 mbps >of throughput? I always thought that in theory that was the case?? It's "statistical" load balancing, according to Cisco. The operation that determines which link in a Fast EtherChannel to use is quite bizarre, and does not provide precise load balancing. It provides load sharing. Think of it like a complex highway system. Adding new highways distributes the load, but it doesn't usually balance the load very precisely. Are you saying it should provide precise load balancing? That would seem to add a scary amount of knowledge that the FEC interface would need to know -- RMON traffic statistics or the like to figure out how to distribute flows. Intuitively, the cost of adding that intelligence would exceed, by far, the cost of throwing more bandwidth at the problem. Recovery after failure would take longer as well, IMHO. The division of traffic across a Fast EtherChannel is based on source/destination pairs, which is usually not very balanced. There are usually some big talkers and receivers. The Ethernet Bundling Controller (EBC) performs an X-OR operation on the last two bits of the source MAC address and the destination MAC address. This operation yields one of four results: (0 0), (0 1), (1 0), or (1 1). Each of these values points to a link in the Fast EtherChannel bundle. Priscilla > Since >the data is transmitted on different wire pairs, if the sender and receiver >transmit at the same time, why isn't 800 mbps possible > _ FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
Re: Equal cost switching
> The Ethernet Bundling Controller (EBC) performs an X-OR operation >on >the last two bits of the source MAC address and the destination >MAC >address. This operation yields one of four results: (0 0), >(0,1), (1 0), >or (1 1). Each of these values points to a link in the >Fast EtherChannel >bundle. That really makes sense. I always pictured this process as the first frame in a stream being sent down the first wire, and the second frame in the stream being down the second wire, third frame being sent down the first wire.. ect.. The way you explain it makes more sense because this way the switch wont have to think about which wire it last used to send a frame, but instead it does a simple calculation. So in essence, if you had 8 wires in an EtherChannel, but most of your traffic was going only between 2 servers ( Server1 <- Switch-> Server2), then only 1 or 2 of the links would be used based on the X-OR calculation? So 6 of the wires in the bundle would be wasted? Is this accurate? Also, I've never really thought about it, but is it possible to have a number of wires in an EtherChannel that are not a power of 2? I.E. 3,5,6,7? It wouldn't seem possible if each wire was assigned a value ((0,0), (0,1), (1,0), (1,1)). If you had 3 wires in an EtherChannel, then the 1,1 value would not be used, and to me, I would think that the Switch would get confused if all the values didn't have an assigned value. One more thing guys! Don't let the hype about fool-duplex full you! If you have a full-duplex 100Mbps connection, you dont REALLY get 200Mbps bandwidth, you just get 100Mbps in both directions simultaneously. Fred Danson >From: Priscilla Oppenheimer <[EMAIL PROTECTED]> >Reply-To: Priscilla Oppenheimer <[EMAIL PROTECTED]> >To: "AndyD" <[EMAIL PROTECTED]>, [EMAIL PROTECTED] >Subject: Re: Equal cost switching >Date: Mon, 19 Feb 2001 11:21:24 -0800 > >At 08:14 AM 2/19/01, AndyD wrote: > >Thanks for all your help. The way I understand it now is that with >multiple > >vlans using different root bridges, you can have different vlans >splitting > >the bandwidth - some going in one direction, some in the other. But if >one > >link goes down, STP will then shift all to the good link. This gives you > >some load balancing and also redundancy. > >Yes, and thanks to the people who provided the details. This is often a >good solution. It has been shown to scale to even very large switched >networks. > > >It looks like you need to go to > >layer 3 switching to do any load balancing other than this. And > >etherchannel is another option for aggregating bandwidth. But someone >said > >with etherchannel using 4 full duplex 100 mbp ports will not give 800 >mbps > >of throughput? I always thought that in theory that was the case?? > >It's "statistical" load balancing, according to Cisco. The operation that >determines which link in a Fast EtherChannel to use is quite bizarre, and >does not provide precise load balancing. It provides load sharing. Think of >it like a complex highway system. Adding new highways distributes the load, >but it doesn't usually balance the load very precisely. > >The division of traffic across a Fast EtherChannel is based on >source/destination pairs, which is usually not very balanced. There are >usually some big talkers and receivers. The Ethernet Bundling Controller >(EBC) performs an X-OR operation on the last two bits of the source MAC >address and the destination MAC address. This operation yields one of four >results: (0 0), (0 1), (1 0), or (1 1). Each of these values points to a >link in the Fast EtherChannel bundle. > >Priscilla > > > Since > >the data is transmitted on different wire pairs, if the sender and >receiver > >transmit at the same time, why isn't 800 mbps possible > > > >Thanks again !! > > > > > > > >""Peter Van Oene"" <[EMAIL PROTECTED]> wrote in message > >[EMAIL PROTECTED]">news:[EMAIL PROTECTED]... > > > Per my other post, STP prevents looping traffic in general, not simply > >broadcasts. > > > > > > Pete > > > > > > > > > *** REPLY SEPARATOR *** > > > > > > On 2/19/2001 at 6:50 AM Kenneth wrote: > > > > > > >Jason is right. This will defeat the purpose of Spanning Tree of >creating > >a > > > >single path to a destination. The primary reason this was designed >was to > > > >prevent broadcast loops. > > > > > > > >If you want to force it to use 2 paths to one destination, use > >
Re: Equal cost switching
At 08:14 AM 2/19/01, AndyD wrote: >Thanks for all your help. The way I understand it now is that with multiple >vlans using different root bridges, you can have different vlans splitting >the bandwidth - some going in one direction, some in the other. But if one >link goes down, STP will then shift all to the good link. This gives you >some load balancing and also redundancy. Yes, and thanks to the people who provided the details. This is often a good solution. It has been shown to scale to even very large switched networks. >It looks like you need to go to >layer 3 switching to do any load balancing other than this. And >etherchannel is another option for aggregating bandwidth. But someone said >with etherchannel using 4 full duplex 100 mbp ports will not give 800 mbps >of throughput? I always thought that in theory that was the case?? It's "statistical" load balancing, according to Cisco. The operation that determines which link in a Fast EtherChannel to use is quite bizarre, and does not provide precise load balancing. It provides load sharing. Think of it like a complex highway system. Adding new highways distributes the load, but it doesn't usually balance the load very precisely. The division of traffic across a Fast EtherChannel is based on source/destination pairs, which is usually not very balanced. There are usually some big talkers and receivers. The Ethernet Bundling Controller (EBC) performs an X-OR operation on the last two bits of the source MAC address and the destination MAC address. This operation yields one of four results: (0 0), (0 1), (1 0), or (1 1). Each of these values points to a link in the Fast EtherChannel bundle. Priscilla > Since >the data is transmitted on different wire pairs, if the sender and receiver >transmit at the same time, why isn't 800 mbps possible > >Thanks again !! > > > >""Peter Van Oene"" <[EMAIL PROTECTED]> wrote in message >[EMAIL PROTECTED]">news:[EMAIL PROTECTED]... > > Per my other post, STP prevents looping traffic in general, not simply >broadcasts. > > > > Pete > > > > > > *** REPLY SEPARATOR *** > > > > On 2/19/2001 at 6:50 AM Kenneth wrote: > > > > >Jason is right. This will defeat the purpose of Spanning Tree of creating >a > > >single path to a destination. The primary reason this was designed was to > > >prevent broadcast loops. > > > > > >If you want to force it to use 2 paths to one destination, use > > >port-channelling which statically load-balances traffic going out of two > > >ports. Statically meaning it creates a list of source-destination MAC > > >address pairs and these pair will communicate from a specific port > > >configured to be part of the port-channel. This is in contrary to Dynamic > > >load-balancing where each packet will go out of each port of the > > >port-channel. > > > > > >With this in mind, if 4 ports are configured for 100 Mbps full-duplex > > >port-channels, this doesn't mean it provides an 800Mbps link. > > > > > > > > > > > > > > >"AndyD" <[EMAIL PROTECTED]> wrote in message > > >96p2uk$rt5$[EMAIL PROTECTED]">news:96p2uk$rt5$[EMAIL PROTECTED]... > > >> Spanning tree is supposed to choose the one best switched path. But if > > >you > > >> set up two equal cost paths, will it use both? Is there a way to force >it > > >> to use the bandwidth from both paths? > > >> > > >> Thanks! > > >> > > >> > > >> _ > > >> FAQ, list archives, and subscription info: > > >http://www.groupstudy.com/list/cisco.html > > >> Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] > > >> > > > > > > > > >_ > > >FAQ, list archives, and subscription info: >http://www.groupstudy.com/list/cisco.html > > >Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] > > > > > > > > _ > > FAQ, list archives, and subscription info: >http://www.groupstudy.com/list/cisco.html > > Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] > > > > >_ >FAQ, list archives, and subscription info: >http://www.groupstudy.com/list/cisco.html >Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] Priscilla Oppenheimer http://www.priscilla.com _ FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
RE: Equal cost switching
Etherchannel decides which link to send a packet over based on a logical operation on the MAC addresses of the source and destination hosts (XOR, I believe). Based on the outcome of the operation, one of the links in the EtherChannel will be selected. For more information, go to the following link: http://www.cisco.com/warp/public/cc/techno/media/lan/ether/channel/prodlit/f aste_an.htm Brant I. Stevens Internetwork Solutions Engineer Thrupoint, Inc. 545 Fifth Avenue, 14th Floor New York, NY. 10017 646-562-6540 -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of AndyD Sent: Monday, February 19, 2001 11:14 AM To: [EMAIL PROTECTED] Subject: Re: Equal cost switching Thanks for all your help. The way I understand it now is that with multiple vlans using different root bridges, you can have different vlans splitting the bandwidth - some going in one direction, some in the other. But if one link goes down, STP will then shift all to the good link. This gives you some load balancing and also redundancy. It looks like you need to go to layer 3 switching to do any load balancing other than this. And etherchannel is another option for aggregating bandwidth. But someone said with etherchannel using 4 full duplex 100 mbp ports will not give 800 mbps of throughput? I always thought that in theory that was the case?? Since the data is transmitted on different wire pairs, if the sender and receiver transmit at the same time, why isn't 800 mbps possible Thanks again !! ""Peter Van Oene"" <[EMAIL PROTECTED]> wrote in message [EMAIL PROTECTED]">news:[EMAIL PROTECTED]... > Per my other post, STP prevents looping traffic in general, not simply broadcasts. > > Pete > > > *** REPLY SEPARATOR *** > > On 2/19/2001 at 6:50 AM Kenneth wrote: > > >Jason is right. This will defeat the purpose of Spanning Tree of creating a > >single path to a destination. The primary reason this was designed was to > >prevent broadcast loops. > > > >If you want to force it to use 2 paths to one destination, use > >port-channelling which statically load-balances traffic going out of two > >ports. Statically meaning it creates a list of source-destination MAC > >address pairs and these pair will communicate from a specific port > >configured to be part of the port-channel. This is in contrary to Dynamic > >load-balancing where each packet will go out of each port of the > >port-channel. > > > >With this in mind, if 4 ports are configured for 100 Mbps full-duplex > >port-channels, this doesn't mean it provides an 800Mbps link. > > > > > > > > > >"AndyD" <[EMAIL PROTECTED]> wrote in message > >96p2uk$rt5$[EMAIL PROTECTED]">news:96p2uk$rt5$[EMAIL PROTECTED]... > >> Spanning tree is supposed to choose the one best switched path. But if > >you > >> set up two equal cost paths, will it use both? Is there a way to force it > >> to use the bandwidth from both paths? > >> > >> Thanks! > >> > >> > >> _ > >> FAQ, list archives, and subscription info: > >http://www.groupstudy.com/list/cisco.html > >> Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] > >> > > > > > >_ > >FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html > >Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] > > > > _ > FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html > Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] > _ FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] _ FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
Re: Equal cost switching
Thanks for all your help. The way I understand it now is that with multiple vlans using different root bridges, you can have different vlans splitting the bandwidth - some going in one direction, some in the other. But if one link goes down, STP will then shift all to the good link. This gives you some load balancing and also redundancy. It looks like you need to go to layer 3 switching to do any load balancing other than this. And etherchannel is another option for aggregating bandwidth. But someone said with etherchannel using 4 full duplex 100 mbp ports will not give 800 mbps of throughput? I always thought that in theory that was the case?? Since the data is transmitted on different wire pairs, if the sender and receiver transmit at the same time, why isn't 800 mbps possible Thanks again !! ""Peter Van Oene"" <[EMAIL PROTECTED]> wrote in message [EMAIL PROTECTED]">news:[EMAIL PROTECTED]... > Per my other post, STP prevents looping traffic in general, not simply broadcasts. > > Pete > > > *** REPLY SEPARATOR *** > > On 2/19/2001 at 6:50 AM Kenneth wrote: > > >Jason is right. This will defeat the purpose of Spanning Tree of creating a > >single path to a destination. The primary reason this was designed was to > >prevent broadcast loops. > > > >If you want to force it to use 2 paths to one destination, use > >port-channelling which statically load-balances traffic going out of two > >ports. Statically meaning it creates a list of source-destination MAC > >address pairs and these pair will communicate from a specific port > >configured to be part of the port-channel. This is in contrary to Dynamic > >load-balancing where each packet will go out of each port of the > >port-channel. > > > >With this in mind, if 4 ports are configured for 100 Mbps full-duplex > >port-channels, this doesn't mean it provides an 800Mbps link. > > > > > > > > > >"AndyD" <[EMAIL PROTECTED]> wrote in message > >96p2uk$rt5$[EMAIL PROTECTED]">news:96p2uk$rt5$[EMAIL PROTECTED]... > >> Spanning tree is supposed to choose the one best switched path. But if > >you > >> set up two equal cost paths, will it use both? Is there a way to force it > >> to use the bandwidth from both paths? > >> > >> Thanks! > >> > >> > >> _ > >> FAQ, list archives, and subscription info: > >http://www.groupstudy.com/list/cisco.html > >> Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] > >> > > > > > >_ > >FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html > >Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] > > > > _ > FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html > Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] > _ FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
Re: Equal cost switching
Depending on the architecture of your network, you can balance the traffic of multiple VLANs across different links by setting the root bridge to opposite switches. So if you have an access layer switch feeding into say 2 catalyst L3 switches, you can set the root bridge for VLAN2 to the first Catalyst and for VLAN3 to the second Catalyst. This will allow you to use bandwidth from both links. This is one of the benefits of PerVLAN Spanning Tree versus a Common Spanning Tree. ""AndyD"" <[EMAIL PROTECTED]> wrote in message 96p2uk$rt5$[EMAIL PROTECTED]">news:96p2uk$rt5$[EMAIL PROTECTED]... > Spanning tree is supposed to choose the one best switched path. But if you > set up two equal cost paths, will it use both? Is there a way to force it > to use the bandwidth from both paths? > > Thanks! > > > _ > FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html > Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] > _ FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
Re: Equal cost switching
Per my other post, STP prevents looping traffic in general, not simply broadcasts. Pete *** REPLY SEPARATOR *** On 2/19/2001 at 6:50 AM Kenneth wrote: >Jason is right. This will defeat the purpose of Spanning Tree of creating a >single path to a destination. The primary reason this was designed was to >prevent broadcast loops. > >If you want to force it to use 2 paths to one destination, use >port-channelling which statically load-balances traffic going out of two >ports. Statically meaning it creates a list of source-destination MAC >address pairs and these pair will communicate from a specific port >configured to be part of the port-channel. This is in contrary to Dynamic >load-balancing where each packet will go out of each port of the >port-channel. > >With this in mind, if 4 ports are configured for 100 Mbps full-duplex >port-channels, this doesn't mean it provides an 800Mbps link. > > > > >"AndyD" <[EMAIL PROTECTED]> wrote in message >96p2uk$rt5$[EMAIL PROTECTED]">news:96p2uk$rt5$[EMAIL PROTECTED]... >> Spanning tree is supposed to choose the one best switched path. But if >you >> set up two equal cost paths, will it use both? Is there a way to force it >> to use the bandwidth from both paths? >> >> Thanks! >> >> >> _ >> FAQ, list archives, and subscription info: >http://www.groupstudy.com/list/cisco.html >> Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] >> > > >_ >FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html >Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] _ FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
Re: Equal cost switching
I don't think you can put a single port on two VLANS unless you configured trunking if my memory serves me right. with Per VLAN spanning tree a particular switch can belong to multiple instances of spanning tree and in each spanning tree instance, it might be acting as a root bridge, some ports might be in blocking mode or forwarding depending on what VLAN it belongs, too. I believe the design that you had drawn shows the access layer switches are trunking to Switch A and B to provide redundancy in case of failure in switch A or B. Also, each switch in the access layer can run up to 2 instances of spanning tree on each VLAN which are carried through the trunk ports only if Cisco switches are used. Link: http://www.cisco.com/univercd/cc/td/doc/product/lan/cat5000/rel_5_2/config/s pantree.htm#xtocid2879614 Priscilla Oppenheimer <[EMAIL PROTECTED]> wrote in message [EMAIL PROTECTED]">news:[EMAIL PROTECTED]... > > >- Original Message - > >From: AndyD <[EMAIL PROTECTED]> > >Newsgroups: groupstudy.cisco > >To: <[EMAIL PROTECTED]> > >Sent: Sunday, February 18, 2001 8:58 AM > >Subject: Equal cost switching > > > > > Spanning tree is supposed to choose the one best switched path. But if > >you > > > set up two equal cost paths, will it use both? > > No, I don't think so. > > > Is there a way to force it > > > to use the bandwidth from both paths? > > Cisco lets you implement one spanning-tree per VLAN. So with redundant > links and VLANs, you can accomplish what you want. I can't remember exactly > how it works, but I think you put every port in two VLANs. I talked about > this in my book, Top-Down Network Design, and you can see the figure for > the design here: > > http://www.priscilla.com/topdownupdates.html > > Hope this helps a bit. Maybe somebody else remembers more details. (I > didn't get into the details in my book, and now I've forgotten them! &;-) > > Priscilla > > > > > > > Thanks! > > > > > > > > Priscilla Oppenheimer > http://www.priscilla.com > > _ > FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html > Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] > _ FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
Re: Equal cost switching
Jason is right. This will defeat the purpose of Spanning Tree of creating a single path to a destination. The primary reason this was designed was to prevent broadcast loops. If you want to force it to use 2 paths to one destination, use port-channelling which statically load-balances traffic going out of two ports. Statically meaning it creates a list of source-destination MAC address pairs and these pair will communicate from a specific port configured to be part of the port-channel. This is in contrary to Dynamic load-balancing where each packet will go out of each port of the port-channel. With this in mind, if 4 ports are configured for 100 Mbps full-duplex port-channels, this doesn't mean it provides an 800Mbps link. "AndyD" <[EMAIL PROTECTED]> wrote in message 96p2uk$rt5$[EMAIL PROTECTED]">news:96p2uk$rt5$[EMAIL PROTECTED]... > Spanning tree is supposed to choose the one best switched path. But if you > set up two equal cost paths, will it use both? Is there a way to force it > to use the bandwidth from both paths? > > Thanks! > > > _ > FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html > Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] > _ FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
Re: Equal cost switching
>- Original Message - >From: AndyD <[EMAIL PROTECTED]> >Newsgroups: groupstudy.cisco >To: <[EMAIL PROTECTED]> >Sent: Sunday, February 18, 2001 8:58 AM >Subject: Equal cost switching > > > Spanning tree is supposed to choose the one best switched path. But if >you > > set up two equal cost paths, will it use both? No, I don't think so. > Is there a way to force it > > to use the bandwidth from both paths? Cisco lets you implement one spanning-tree per VLAN. So with redundant links and VLANs, you can accomplish what you want. I can't remember exactly how it works, but I think you put every port in two VLANs. I talked about this in my book, Top-Down Network Design, and you can see the figure for the design here: http://www.priscilla.com/topdownupdates.html Hope this helps a bit. Maybe somebody else remembers more details. (I didn't get into the details in my book, and now I've forgotten them! &;-) Priscilla > > > > Thanks! > > Priscilla Oppenheimer http://www.priscilla.com _ FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
Re: Equal cost switching
That is why I said the main reason not the only reason. Normally, before Node A sends any packet, it will do ARP, this will create loop immediately. Not so normal, you can hard coded the ARP cache. Jack ""Peter Van Oene"" <[EMAIL PROTECTED]> wrote in message [EMAIL PROTECTED]">news:[EMAIL PROTECTED]... > This is actually not the case. A layer two network that contains a logical loop with get into trouble with all types of traffic flows. For example, consider a simple network like the one I'll try and draw below. > > > Node A Node B >| | > -Ethernet 1--- > | | > Bridge A Bridge B > | | > --Ethernet 2-- > > Consider a transmission from Node A to Node B and assume that both nodes were recently powered up and that the bridge tables for the two bridges have not been built. > > Here is a likely scenario. The frame hits Ethernet 1 and both bridge A and B detect the packet and check their forwarding tables only to realize they do not have an entry for B. At this time they add Node A to the forwarding table as residing on Ethernet 1. They then both forward the frame onto Ethernet 2. Node B also receives the frame and processes it. However, 2 versions of the frame now exist on or headed two Ethernet 2. When the bridges forward to Ethernet 2, (1 at a time) each bridge will process the others frame and decide that A has indeed moved to Ethernet 2 and adjust their forwarding tables appropriately. Assuming B hasn't responded as yet, they will also process each others frames and still not finding B in their forwarding table, copy them back onto Ethernet 1. However, when they do, they will again switch A's address from Ethernet 2 to 1 and likely repeat the process again. > > Just think what happens when B responds :) > > All in all, this is very unhealthy. The fact that there is no way at layer 2 in ethernet to detect the age of frames severely hinders loop mitigation. In fact, there pretty much isn't any loop mitigation at layer 2 in ethernet networks. If you create a looped topology and do not prune the redundant paths, you will bring a network down in seconds. > > Pete > > > *** REPLY SEPARATOR *** > > On 2/18/2001 at 4:58 PM Jack Yu wrote: > > >Actually, the main reason to eliminate multiple paths is because of > >broadcast at layer 2. Lay 2 devices have to this forward broadcast, and > >multiple paths to a single destination will cause broadcast storm. Layer 3 > >devices do not have this problem only because they do not forward broadcast, > >they either read it or drop it. So if there is a network with no layer 2 > >broadcast, you do not need spanning tree at all. Of course, you can also > >disable it when you are sure there is no duplicated path exists. > > > >Regards, > >Jack > > > > > > > > > >""Groupstudy"" <[EMAIL PROTECTED]> wrote in message > >[EMAIL PROTECTED]">news:[EMAIL PROTECTED]... > >> Spanning Tree's job is to eliminate multiple paths to a single > >destination. > >> If it finds more than one path it will put one of them into blocking mode > >to > >> ensure a loop free path. Remember, Spanning Tree runs at layer two and > >has > >> no concept bandwidth. If you need to setup equal cost paths to a certain > >> destination, you will need to do it at layers above layer two. > >> > >> Pick up a copy of Radia Perlmans 'Interconnections' second edition. Radia > >> is the primary authority on the Spanning Tree algorithm, she will > >enlighten > >> you. This is also good solid study for deeper networking knowledge. > >> > >> - Original Message - > >> From: AndyD <[EMAIL PROTECTED]> > >> Newsgroups: groupstudy.cisco > >> To: <[EMAIL PROTECTED]> > >> Sent: Sunday, February 18, 2001 8:58 AM > >> Subject: Equal cost switching > >> > >> > >> > Spanning tree is supposed to choose the one best switched path. But if > >> you > >> > set up two equal cost paths, will it use both? Is there a way to force > >it > >> > to use the bandwidth from both paths? > >> > > >> > Thanks! > >> > > >> > > >> > _ > >> > FAQ, list archives, and subscription info: > >> http://www.groupstudy.com/list/cisco.html > >> > Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] > >> > > >> > >> _ > >&
Re: Equal cost switching
I cann't and did not promise or intend to so. ""Groupstudy"" <[EMAIL PROTECTED]> wrote in message [EMAIL PROTECTED]">news:[EMAIL PROTECTED]... > Give me an example of a network where layer two has no broadcasts please... > > - Original Message - > From: Jack Yu <[EMAIL PROTECTED]> > Newsgroups: groupstudy.cisco > To: <[EMAIL PROTECTED]> > Sent: Sunday, February 18, 2001 1:58 PM > Subject: Re: Equal cost switching > > > > Actually, the main reason to eliminate multiple paths is because of > > broadcast at layer 2. Lay 2 devices have to this forward broadcast, and > > multiple paths to a single destination will cause broadcast storm. Layer 3 > > devices do not have this problem only because they do not forward > broadcast, > > they either read it or drop it. So if there is a network with no layer 2 > > broadcast, you do not need spanning tree at all. Of course, you can also > > disable it when you are sure there is no duplicated path exists. > > > > Regards, > > Jack > > > > > > > > > > ""Groupstudy"" <[EMAIL PROTECTED]> wrote in message > > [EMAIL PROTECTED]">news:[EMAIL PROTECTED]... > > > Spanning Tree's job is to eliminate multiple paths to a single > > destination. > > > If it finds more than one path it will put one of them into blocking > mode > > to > > > ensure a loop free path. Remember, Spanning Tree runs at layer two and > > has > > > no concept bandwidth. If you need to setup equal cost paths to a > certain > > > destination, you will need to do it at layers above layer two. > > > > > > Pick up a copy of Radia Perlmans 'Interconnections' second edition. > Radia > > > is the primary authority on the Spanning Tree algorithm, she will > > enlighten > > > you. This is also good solid study for deeper networking knowledge. > > > > > > - Original Message - > > > From: AndyD <[EMAIL PROTECTED]> > > > Newsgroups: groupstudy.cisco > > > To: <[EMAIL PROTECTED]> > > > Sent: Sunday, February 18, 2001 8:58 AM > > > Subject: Equal cost switching > > > > > > > > > > Spanning tree is supposed to choose the one best switched path. But > if > > > you > > > > set up two equal cost paths, will it use both? Is there a way to > force > > it > > > > to use the bandwidth from both paths? > > > > > > > > Thanks! > > > > > > > > > > > > _ > > > > FAQ, list archives, and subscription info: > > > http://www.groupstudy.com/list/cisco.html > > > > Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] > > > > > > > > > > _ > > > FAQ, list archives, and subscription info: > > http://www.groupstudy.com/list/cisco.html > > > Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] > > > > > > > > > _ > > FAQ, list archives, and subscription info: > http://www.groupstudy.com/list/cisco.html > > Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] > > > > _ > FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html > Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] > _ FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
Re: Equal cost switching
Give me an example of a network where layer two has no broadcasts please... - Original Message - From: Jack Yu <[EMAIL PROTECTED]> Newsgroups: groupstudy.cisco To: <[EMAIL PROTECTED]> Sent: Sunday, February 18, 2001 1:58 PM Subject: Re: Equal cost switching > Actually, the main reason to eliminate multiple paths is because of > broadcast at layer 2. Lay 2 devices have to this forward broadcast, and > multiple paths to a single destination will cause broadcast storm. Layer 3 > devices do not have this problem only because they do not forward broadcast, > they either read it or drop it. So if there is a network with no layer 2 > broadcast, you do not need spanning tree at all. Of course, you can also > disable it when you are sure there is no duplicated path exists. > > Regards, > Jack > > > > > ""Groupstudy"" <[EMAIL PROTECTED]> wrote in message > [EMAIL PROTECTED]">news:[EMAIL PROTECTED]... > > Spanning Tree's job is to eliminate multiple paths to a single > destination. > > If it finds more than one path it will put one of them into blocking mode > to > > ensure a loop free path. Remember, Spanning Tree runs at layer two and > has > > no concept bandwidth. If you need to setup equal cost paths to a certain > > destination, you will need to do it at layers above layer two. > > > > Pick up a copy of Radia Perlmans 'Interconnections' second edition. Radia > > is the primary authority on the Spanning Tree algorithm, she will > enlighten > > you. This is also good solid study for deeper networking knowledge. > > > > ----- Original Message - > > From: AndyD <[EMAIL PROTECTED]> > > Newsgroups: groupstudy.cisco > > To: <[EMAIL PROTECTED]> > > Sent: Sunday, February 18, 2001 8:58 AM > > Subject: Equal cost switching > > > > > > > Spanning tree is supposed to choose the one best switched path. But if > > you > > > set up two equal cost paths, will it use both? Is there a way to force > it > > > to use the bandwidth from both paths? > > > > > > Thanks! > > > > > > > > > _ > > > FAQ, list archives, and subscription info: > > http://www.groupstudy.com/list/cisco.html > > > Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] > > > > > > > _ > > FAQ, list archives, and subscription info: > http://www.groupstudy.com/list/cisco.html > > Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] > > > > > _ > FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html > Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] > _ FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
Re: Equal cost switching
This is actually not the case. A layer two network that contains a logical loop with get into trouble with all types of traffic flows. For example, consider a simple network like the one I'll try and draw below. Node A Node B || -Ethernet 1--- | | Bridge A Bridge B | | --Ethernet 2-- Consider a transmission from Node A to Node B and assume that both nodes were recently powered up and that the bridge tables for the two bridges have not been built. Here is a likely scenario. The frame hits Ethernet 1 and both bridge A and B detect the packet and check their forwarding tables only to realize they do not have an entry for B. At this time they add Node A to the forwarding table as residing on Ethernet 1. They then both forward the frame onto Ethernet 2. Node B also receives the frame and processes it. However, 2 versions of the frame now exist on or headed two Ethernet 2. When the bridges forward to Ethernet 2, (1 at a time) each bridge will process the others frame and decide that A has indeed moved to Ethernet 2 and adjust their forwarding tables appropriately. Assuming B hasn't responded as yet, they will also process each others frames and still not finding B in their forwarding table, copy them back onto Ethernet 1. However, when they do, they will again switch A's address from Ethernet 2 to 1 and likely repeat the process again. Just think what happens when B responds :) All in all, this is very unhealthy. The fact that there is no way at layer 2 in ethernet to detect the age of frames severely hinders loop mitigation. In fact, there pretty much isn't any loop mitigation at layer 2 in ethernet networks. If you create a looped topology and do not prune the redundant paths, you will bring a network down in seconds. Pete *** REPLY SEPARATOR *** On 2/18/2001 at 4:58 PM Jack Yu wrote: >Actually, the main reason to eliminate multiple paths is because of >broadcast at layer 2. Lay 2 devices have to this forward broadcast, and >multiple paths to a single destination will cause broadcast storm. Layer 3 >devices do not have this problem only because they do not forward broadcast, >they either read it or drop it. So if there is a network with no layer 2 >broadcast, you do not need spanning tree at all. Of course, you can also >disable it when you are sure there is no duplicated path exists. > >Regards, >Jack > > > > >""Groupstudy"" <[EMAIL PROTECTED]> wrote in message >[EMAIL PROTECTED]">news:[EMAIL PROTECTED]... >> Spanning Tree's job is to eliminate multiple paths to a single >destination. >> If it finds more than one path it will put one of them into blocking mode >to >> ensure a loop free path. Remember, Spanning Tree runs at layer two and >has >> no concept bandwidth. If you need to setup equal cost paths to a certain >> destination, you will need to do it at layers above layer two. >> >> Pick up a copy of Radia Perlmans 'Interconnections' second edition. Radia >> is the primary authority on the Spanning Tree algorithm, she will >enlighten >> you. This is also good solid study for deeper networking knowledge. >> >> ----- Original Message - >> From: AndyD <[EMAIL PROTECTED]> >> Newsgroups: groupstudy.cisco >> To: <[EMAIL PROTECTED]> >> Sent: Sunday, February 18, 2001 8:58 AM >> Subject: Equal cost switching >> >> >> > Spanning tree is supposed to choose the one best switched path. But if >> you >> > set up two equal cost paths, will it use both? Is there a way to force >it >> > to use the bandwidth from both paths? >> > >> > Thanks! >> > >> > >> > _ >> > FAQ, list archives, and subscription info: >> http://www.groupstudy.com/list/cisco.html >> > Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] >> > >> >> _ >> FAQ, list archives, and subscription info: >http://www.groupstudy.com/list/cisco.html >> Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] >> > > >_ >FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html >Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] _ FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
Re: Equal cost switching
Actually, the main reason to eliminate multiple paths is because of broadcast at layer 2. Lay 2 devices have to this forward broadcast, and multiple paths to a single destination will cause broadcast storm. Layer 3 devices do not have this problem only because they do not forward broadcast, they either read it or drop it. So if there is a network with no layer 2 broadcast, you do not need spanning tree at all. Of course, you can also disable it when you are sure there is no duplicated path exists. Regards, Jack ""Groupstudy"" <[EMAIL PROTECTED]> wrote in message [EMAIL PROTECTED]">news:[EMAIL PROTECTED]... > Spanning Tree's job is to eliminate multiple paths to a single destination. > If it finds more than one path it will put one of them into blocking mode to > ensure a loop free path. Remember, Spanning Tree runs at layer two and has > no concept bandwidth. If you need to setup equal cost paths to a certain > destination, you will need to do it at layers above layer two. > > Pick up a copy of Radia Perlmans 'Interconnections' second edition. Radia > is the primary authority on the Spanning Tree algorithm, she will enlighten > you. This is also good solid study for deeper networking knowledge. > > - Original Message - > From: AndyD <[EMAIL PROTECTED]> > Newsgroups: groupstudy.cisco > To: <[EMAIL PROTECTED]> > Sent: Sunday, February 18, 2001 8:58 AM > Subject: Equal cost switching > > > > Spanning tree is supposed to choose the one best switched path. But if > you > > set up two equal cost paths, will it use both? Is there a way to force it > > to use the bandwidth from both paths? > > > > Thanks! > > > > > > _ > > FAQ, list archives, and subscription info: > http://www.groupstudy.com/list/cisco.html > > Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] > > > > _ > FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html > Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] > _ FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
Re: Equal cost switching
Spanning Tree's job is to eliminate multiple paths to a single destination. If it finds more than one path it will put one of them into blocking mode to ensure a loop free path. Remember, Spanning Tree runs at layer two and has no concept bandwidth. If you need to setup equal cost paths to a certain destination, you will need to do it at layers above layer two. Pick up a copy of Radia Perlmans 'Interconnections' second edition. Radia is the primary authority on the Spanning Tree algorithm, she will enlighten you. This is also good solid study for deeper networking knowledge. - Original Message - From: AndyD <[EMAIL PROTECTED]> Newsgroups: groupstudy.cisco To: <[EMAIL PROTECTED]> Sent: Sunday, February 18, 2001 8:58 AM Subject: Equal cost switching > Spanning tree is supposed to choose the one best switched path. But if you > set up two equal cost paths, will it use both? Is there a way to force it > to use the bandwidth from both paths? > > Thanks! > > > _ > FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html > Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] > _ FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
Re: Equal cost switching
It will not use both paths as that would defeat the purpose of spanning tree. To force the paths to both be used, you would have to configure the ports in a channel. There should be plenty of good information about spanning tree operation and port channeling at www.cisco.com Jason Fletcher "AndyD" wrote in message <96p2uk$rt5$[EMAIL PROTECTED]>... >Spanning tree is supposed to choose the one best switched path. But if you >set up two equal cost paths, will it use both? Is there a way to force it >to use the bandwidth from both paths? > >Thanks! > > >_ >FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html >Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] > _ FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
Equal cost switching
Spanning tree is supposed to choose the one best switched path. But if you set up two equal cost paths, will it use both? Is there a way to force it to use the bandwidth from both paths? Thanks! _ FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
