Switches? How many are too many on a network.

Posted on 2005-03-11
Medium Priority
Last Modified: 2008-02-01
I am administering a Windows 2003 LAN in a factory setting. On doing an audit of the plant in preparation for adding two users in a prefab office on the oher end of the facility it really dawned onme that we have alot of switches in place. have a look at the diagram below.... can anyone tell me if this is a bad setup, I am limited do to the physical setup of the building, but if this isnt good and anyone has sugestions I would love to hear them. Also any suggestions on how to handle the far side of the plant--any negatives in connecting a workgroup switch, which is connected to another workgroup switch which is connected to a larger switch?

                     3com 2024 - 3 Windows 2003 servers, Unix server, printers
                        3com 2024 16 users
                       3com 2024 - 8 users
                           3Com 2024 |(other side of plant about 200ft--only connection to this switch is the workgroup switch about 30ft away)               |
                  Linksys Workgroup switch - 2 users
                   Linksys Workgroup Switch (I will be adding this one,thus connecting the one prefab office to the other)    2 users      
Question by:kevotron
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Accepted Solution

j3ggs earned 500 total points
ID: 13517832
Hi kevotron,

Depending on how the physical location of these, I would do the following:

|   |         |
|   |         |
| 8 Users  |
|              |
16 Users   |
       3COM 200Ft Away
             |       |
             |   Linksys

Sorry the diagram is so bad. Basically you want to make the users as close to the servers as possible (i.e. with the least switch path). Depending on whether these things support spanning-tree you could also put some redundant links in between..... but lets not get ahead of ourselves!

To sum up, make the server switch your core, then attach the switches that are in the same physical location directly to it. Then have a second "core" in your other location, but bring that in to the core of your 1st location.

This probably wont make too much of a difference on speed, unless the links are heavily utilised. What this will mean is that each switch would have say 100Mb bandwidth to the servers, rather that 2 or 3 switches sharing the same 100Mb link.

Hope this helps.



Expert Comment

ID: 13517937
If I understand your diagram and these devices are connected to each other by a crossover cable than I am actually surprised it works.  I not I am sorry for the confusion.

You asked about connecting a workgroup switch, which is connected to another workgroup switch which is connected to a larger switch. This configuration will work great but is about the limit I would go. I would not put another switch off of the 2nd workgroup switch.

The best way is to have the larger best switch connected to the servers core infrastructure and then all other switches feed off of that.

As far as your connection in the back of the factory, fiber is probably the best choice. It is resistant to EMF (interferance) that a factory typically has and can go for very long distances. Put a fiber port into your large core switch near the servers, run fiber to the back of the factory and connect it to another switch which feeds the workstations. Fiber has really come down in price over the last several years.

Also, I tend to avoid Linksys in the business environment and stick to Cisco's and 3COM. We have found them (others may disagree) to be the most reliable.

Expert Comment

ID: 13518290
A quick comment, I agree with the fibre above, however not sure if these switches even can take fibre?

Also, depending on the spec of the switches, I believe the recomended limitation is a 7 switch network, i.e. a core, and then 3 legs of of that:


I also agree, stick with 3COM or Cisco, my pref is Cisco, I have had lots of problems with 3COM. Even if you go the real low end stuff with Cisco which are'nt expensive they are still damn good.

just my £1 worth.


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Expert Comment

ID: 13518385
The only real things to worry about are making sure you don't create a loop by accidentally plugging in two uplinks without some kind of bonding (Nortel calls it trunking, Cisco calls it Fast Ether Channel) or Spanning Tree.

The other thing you create with chained switches is increased Latency.  Depending on the type of switching involved, ever time you connect a switch to a switch you add a few milli-seconds of latency.  Eventually, it adds up.  If this is acceptable to you and your users no problems.

Ideally, you would have a faster backbone - such as GigE fiber connecting your access switches (which your users plug into) going into Distribution switches which in turn would go into your Core level switches.  Some networks collapse core and distribution into one switch, or access and distribution into one switch and still have core.

This is from:  http://searchnetworking.techtarget.com/tip/1,289483,sid7_gci993444,00.html (You might need to create a free account to read more)

Cisco has defined a hierarchical model known as the hierarchical internetworking model. This model simplifies the task of building a reliable, scalable, and less expensive hierarchical internetwork because rather than focusing on packet construction, it focuses on the three functional areas, or layers, of your network:

Core layer: This layer is considered the backbone of the network and includes the high-end switches and high-speed cables such as fiber cables. This layer of the network does not route traffic at the LAN. In addition, no packet manipulation is done by devices in this layer. Rather, this layer is concerned with speed and ensures reliable delivery of packets.

Distribution layer: This layer includes LAN-based routers and layer 3 switches. This layer ensures that packets are properly routed between subnets and VLANs in your enterprise. This layer is also called the Workgroup layer.

Access layer: This layer includes hubs and switches. This layer is also called the desktop layer because it focuses on connecting client nodes, such as workstations to the network. This layer ensures that packets are delivered to end user computers.

-------------------END PASTE----------------------

Hope this helps

Expert Comment

ID: 13520549
As pseudocyber said, latency is all you really have to worry about.  You may be thinking back to the 5-4-3 rule but switches aren't like hubs so you don't have to worry about the number of nodes between your furthest comp and your switch.  Just remember, the longer the chain, the more computers go down if a switch close to the server fails.

I agree with others that you should have a fast backbone but fiber is expensive.  You could always get a gigabit switch and run a STP Cat 5e line for the same speeds and you wouldn't have to worry about EMI, just differences in ground voltages.  The 3Com 2226 is a nice 10/100 switch with 2 GigE ports, just a step up from your current 3Coms.

Also, others have mentioned 3Com and Cisco switches, but you may want to check out HP switches too. I've been buying them lately and they've been very stable and reliable.  They also come with a nice lifetime warranty.

LVL 10

Expert Comment

ID: 13521035
In the real world with legacy networks many switches will be looped together, the problems have been outlined above, eg if one of the switches fail you lose the server from some locations.

If users aren't complaining be happy, just make sure you have a spare switch handy (big enough to replace any of the switches) just in case one fails.

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