Multiple Switches On A Network?

[slaughteredlamb]

I can't say that I really understand Switches on a network but I'm wondering if our current network configuration might be the reason why our network slows to a crawl from time to time.

We used to have two switches, two 3Com 3870 - 48 port ones. One of these was set as Master 1 and the other set as Slave 2 and some kind of cable linked them at the back. Like this everything worked fine.

We now have three switches, the above 3Com's still set up as they were and a Dell Powerconnect 2724. The only cable that links this to the other switches is a CAT 5 which bridges to one of the 3Com's.

I notice that you can stack up to 8 of the 3Com switches together and clearly there must be a reason for wanting to do this. I mean what is the difference between having 8 separate switches each linked together via a CAT 5 bridging 1 port of one switch to a port on another switch compared to having 8 3Com ones stacked together via this cable at the back other than in going the 3Com route you wouldn't loose 1 port on each switch just for bridging?

What I'm getting at is could the fact that we have two 'paired' switches and a standalone 3rd (linked via a CAT5) be part of the reason we get random slow downs?

I'm looking to rewire our network in the next few weeks anyway as I want to get a second network card installed in the server and set it up for load balancing and then to try and get all the PC's onto two of the switches and then have one switch going to one network card and the other going to the other network card (alternatively I could have both 3Com switches going to one network card and the Dell Switch going to the other).

[Matt]

It could be that the switch linked by the cat5 is running at something silly like 10mb and the 3com cable runs at something like a GB

The more switches you have, obviously the slower your network will be - we have had random slowdowns recently and after making sure it wasnt a loop back we have put it down to faulty mini hubs and switches around the network, some of the cheaper ones and not the managed HP switches we have several off (I think 50 at the last count!) So we are working to take these off and all network points must originate from a switch which should go back via fibre to the central switch striaght away, not daisy chaning off others.

Not sure if that helps you at all actually, sorry!

[Whatever]

It shouldn't be SL.

What is the actual cabling like? This can have a massive effect on the speed and performance. we had one customer who had some Cat 5, some Cat5e and some Cat 6 and the difference in speed and performance was amazing. The terminations (if not shop bought cables) will also have a bearing.

Matt, I wouldn't agree with your statement "The more switches you have, obviously the slower your network will be". It really depends on how the network has been put together. We cable for a multi-national company who have fibre backbones, then Cat 6 to the desk and this works very well, despite the amount of users and large files being transferred.

[Granty]

I can't say that I really understand Switches on a network but I'm wondering if our current network configuration might be the reason why our network slows to a crawl from time to time.

It's possible.

We used to have two switches, two 3Com 3870 - 48 port ones. One of these was set as Master 1 and the other set as Slave 2 and some kind of cable linked them at the back. Like this everything worked fine.

We now have three switches, the above 3Com's still set up as they were and a Dell Powerconnect 2724. The only cable that links this to the other switches is a CAT 5 which bridges to one of the 3Com's.

I notice that you can stack up to 8 of the 3Com switches together and clearly there must be a reason for wanting to do this. I mean what is the difference between having 8 separate switches each linked together via a CAT 5 bridging 1 port of one switch to a port on another switch compared to having 8 3Com ones stacked together via this cable at the back other than in going the 3Com route you wouldn't loose 1 port on each switch just for bridging?

It sounds like the first two switches are connected via a stacking cable which has a number of benefits including throughout ("10Gbps full duplex stacking ports— 40Gbps total stacking bandwidth— for stacking of up to eight units high" for your 3COM). The most you will get out of a CAT5 cable depends on the switch port you are plugging into (1GB max in this case) unless you consider port aggregation which complicates matters.  Another benefit of stacking is that it saves you using ports to connect switches together as you mention.

What I'm getting at is could the fact that we have two 'paired' switches and a standalone 3rd (linked via a CAT5) be part of the reason we get random slow downs?

Possibly. Do you know if your switches have any configuration on them or are they simply out the box? Having looked up the 3COM switch mentioned, the ports auto-negotiate between 10/100/1000.  It could be that the switch ports are configured to one of 10/100/1000 manually or auto-negoiating with the Dell switch at 10/100.  1GB for connecting switches ("uplink ports") should be plenty.

As an example, if you have 96 hosts on the two 48 port 3COM switches trying to download/upload to a server which is plugged into the Dell switch connected via a CAT5 cable which is running at 10 (as opposed to 100/1000) via a port on one of the 48 port switches then you will notice performance issues.

I'm looking to rewire our network in the next few weeks anyway as I want to get a second network card installed in the server and set it up for load balancing and then to try and get all the PC's onto two of the switches and then have one switch going to one network card and the other going to the other network card (alternatively I could have both 3Com switches going to one network card and the Dell Switch going to the other).

Both the 3COM and Dell switches mentioned have SFP slots you could purchase SFP fibre transceivers and connect them with fibre leads though that is probably overkill for your setup. As a start, I'd recommend logging onto the switches (via console/telnet/ssh or possibly web) and checking the configurations.

[Matt]

I meant little unmanaged switches and hubs. Our site has loads of siwtches which are managed linked via fibres but it's where we have used mini switches etc that we have noticed slowdowns

It shouldn't be SL.

What is the actual cabling like? This can have a massive effect on the speed and performance. we had one customer who had some Cat 5, some Cat5e and some Cat 6 and the difference in speed and performance was amazing. The terminations (if not shop bought cables) will also have a bearing.

Matt, I wouldn't agree with your statement "The more switches you have, obviously the slower your network will be". It really depends on how the network has been put together. We cable for a multi-national company who have fibre backbones, then Cat 6 to the desk and this works very well, despite the amount of users and large files being transferred.

[slaughteredlamb]

Cheers all!

My current thinking is that the switches probably are not the cause of the slow down and that instead it is the fact that we are simply trying to put too much data through one network card and if it's not that then it is our cabling which I know was tested to Gigabit speeds when it was commissioned and passed easily but I think it's only running CAT5, certainly when it was installed we only had 10/100 switches.

Seeing as the first and by far the easiest and cheapest thing to do is to add a second network card then sorting out the switches still needs to be done.

One final question then.

Seeing as the two 3Com switches are linked together and need to be in that we need to be able to access the Internet on all PC's, if I were to use just these would I be able to set-up two network cards with load balancing or does this only work if you had two entirely separate switches?

[Whatever]

My current thinking is that the switches probably are not the cause of the slow down and that instead it is the fact that we are simply trying to put too much data through one network card and if it's not that then it is our cabling which I know was tested to Gigabit speeds when it was commissioned and passed easily but I think it's only running CAT5, certainly when it was installed we only had 10/100 switches.

Is it Cat 5 or Cat 5e, there is a difference. When you say it passed easily, do you have any results showing the headroom? The main cause of failure we find is NEXT/FEXT which is lack of maintaining the twist right up to the IDC connection and also the pairs not being spaced after termination. At higher speeds the data will jump across between pairs.

[slaughteredlamb]

According to the wiring diagrams I have the cable used was CAT5e. In terms of the speed test, to be honest I can't remember as it was 8 years ago, I can't find the document and I joined the company 2/3rds of the way through the installation. All I can remember is that when I asked the wireman who was installing it he said that "the network was effectively a Gigabit network but couldn't be badged as such because the cables aren't officially Gigabit cables, however we tested the network at Gigabit speeds and it easily reached it" At the time he was only briefed and paid to install a 10/100 network as at that time our audio network used fibre optic. We haven't used fibre optic for around 5 years now and so everything now goes over the CAT5e