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We've already implemented an extended star network with a central server but we were wondering how we can improve it.

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When you say small - how small? How many devices on your network? How are these physically and logically arranged? It may make sense to split up into subnets based on location, or department, but it really depends on your specific size. Also, you say you want to improve it. What sort of problems are you looking to fix? If it isn't broken don't fix it. – dunxd Nov 14 '10 at 13:11
We've about 50 computers. Precisely I want to know whether star or tree topology we should use.. – Alexander Suraphel Nov 14 '10 at 13:19

I'm inclined to say that your current physical network topology should reflect at least the following four things:

  1. Current (and known future) physical layout of the campus - e.g. there's no need to divide rooms into subnets if they're physically next to one another and serve the same purpose, but there might be a case to divide computers into different subnets if they're in different buildings.

  2. An eye to potential growth and where you as a network manager and your employer as an establishment want to move towards from a strategic point of view - you need to consider what sort of numbers you might have in the future, and where and how these will be used. This might help make certain options look more logical. The network I manage now is 70% bigger than the one that existed when I started working for the college I'm at now, and much more sophisticated; but we always designed our upgrades and changes with an overall eye on where we were going so each change was a reasonably painless stepping stone to the next one.

  3. Security - There are certain considerations here that might point you towards certain decisions - e.g. do you want an "administration" network for running the "business" of the school to be kept separate/heavily firewalled from the "academic" network (there are arguments for and against both, and the biggest decider might be which one fits the culture of the school the best). Do you want to keep certain classrooms separate/firewalled off from the "main" academic network?

  4. An appropriate level of resiliency - how much will it disrupt learning if you have a classroom get knocked offline? Do your students take exams 'electronically', either from a server on your LAN or via the Internet, and if so what happens if there's an outage? Can you afford a "network backbone" with two redundant links to each local switch?

There's no right or wrong answers, or list of "must buy" equipment, as I'm sure you already know, just questions you need to ask yourself to help with the design you're working towards.

I've recently done a lot of design and build work on the network for my college's new campus... we spent about £500,000 on networking, all told, which gave us Cat6 connections from each classroom to the 'local' cabinet, and a backbone with multiple redundant 10Gbe links from each local cabinet to the core, each local cabinet to its 'neighbours' and a 10Gbe connection directly into this backbone for most of our servers (the ones that would benefit). In terms of your comment about star vs. tree topology, we've essentially gone for a 'wheel' topology, i.e. a star topology with links between the spokes too.

That was appropriate for us... it will be overkill for some and small potatoes for others, but mine and my bosses answers to those 4 questions were a big help in designing our network.

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If you have a small network, it is acceptable to have all the machines in one subnet.

When your network starts to grow, you have to consider implementing several subnets. Otherwise, your network will be harder to manage and the overall performance will degrade gradually.

For example, each subnet can be used by a different department/section. Then, these subnets can be interconnected using a router or layer-3 switch.

Larger networks can be composed of multiple layers of connectivity to provide better performance and manageability.

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