Network design reference

Can someone provide me with a reference on small to small-middle sized LAN planning?
I've got a LAN which is growing.
It had 3 GB 24 port switches and now has 4
We need more ports for clients and I wonder at at what point one should do something other than interconnect identical switches.
Also interested in whether to concentrate to servers on one switch and  the workstations on another. (or some other strategy)
I can buy a book if needed.
It's all MS: Windows 2003/8, Exchange 2007, OCS, SQL, Vista, all workstations are GB NICs.
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Carol ChisholmAsked:
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can depend on the backhaul ( the amount of bandwidth available on the backplane).
And the amount of 'intelligence' in managed switches as they can have limitations with number of MAC's per port, but if they are just dumb layer 2 switches, I know of no specific limitation anyone has met.
most upgrades seem to come from added functionality (like management), or increases in bandwidth, 10Gig ports for server etc..

Or many are now getting layer 3 switches and arranging VLAN's within the office..

Powered Ethernet is getting more popular.

As are redundant links..
Carol ChisholmAuthor Commented:
They are just dumb layer 2 switches.
What do you mean by backplane?
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each switch has an internal backplane which is the maximum amount of data that can flow through the switch at any moment.

That would be all ports data communication added together, over a second.
So a 24 Port Hub, running at 1Gig continuously, would require a 24Gig backplane.
I'd bet money your one is not that high, but unless that becomes a problem with retransmissions and failures, it is rarely an issue.

Carol ChisholmAuthor Commented:
No problems, so I just keep adding switches?
And what about what I plug into which switch?
Carol ChisholmAuthor Commented:
Why would I want a VLAN? Everyone access the same data and apps.
Carol ChisholmAuthor Commented:
I'd still be interested in a basic reference covering these topics.
obviously, spanning the switches puts a greater load on them, and if all your servers are on the last switch, and most of the active clients are on the first, that is a lot of data going across four switches..

If you had port mirroring, you could sniff the links and look at the utilization of the links under load, otherwise you'll need specialized testing equipment.

Another way is to keep your eye on the network stats of the interfaces in question (usually servers) by using network monitor (included in server) or intermittently by using netstat -e and 'netsh interface ip show interface'

A basic tree design can support thousands of nodes. If one of your 24-port switches were the "root" of the tree, and each of its ports were used to connect another 24-port switch, you could connect 552 devices and any two would only be 2 hops away.  The main thing to keep in mind as your ethernet  LAN grows is the 5-4-3 rule.  A tree design is solid as long as any two devices are no more than 5 segments apart, with no more than 4 switches in between, and no more than 3 of those segments populated with user devices.  The "root" switch in the example above, since it has no user devices attached, would not contribute to the "3" rule.  If you work out some examples you'll see that a tree design can become quite large.  I.e. the 5-4-3 rule would still be satisfied if the 552 devices were (again) 24-port switches, supporting over 12,000 nodes.  Any two devices in this case would be at most 4 segments away.

If you want to locate your servers the minimum distance away from any node in the tree design, consider placing them on the root switch.  If all your switches connect to the root, the servers will be only 2 hops away from any workstation.  With a small network, it's certainly OK to put user devices on the root switch.

The worst layout with your equipment would be connecting them in a line: Switch1-Switch2-Switch3-Switch4-Switch5. There's a lot of unnecessary latency passing traffic between Switch1 and Switch5. But worst of all, if the servers were connected to Switch2, then the link between Switch2 and Switch3 is also passing traffic for all the devices on Switch4 and Switch5. A good revision to this would be to choose one of them to be the root, and connect them all directly to it, and connect the servers to the root.  This ensures at most 23 devices are sharing a 1 GB uplink.

If you notice your uplinks are very busy and users are complaining that access to the server is slow, you should then consider trunking.  This is done by enabling Spanning Tree Protocol on all the switches, then connecting a second uplink to the root switch, setting both uplinks to trunk mode.

Check out Microsoft's Technet Library for more detail:

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That's the old coax methodology, no need for 5-4-3 now with buffered switches, just keep plugging and praying it doesn't break something.

You can buy a book, but start by getting the manual out for your switches and finding out what they can do..


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