badly in need of network advice


The back story: We have a building with 6 separate companies all using the same network to access the internet/print. All we have is an asdl router/firewall connected to a hub and then patched in to various ports around the office. We can have ~30 computers on the network at anyone time so if we run out of ports I just uplink another hub...end of!

We are just about to by a nice and shiny new server for our network and I heard (via a friend) about vlans and the possibility of splitting the network in to smaller networks (1 for each comp) but still share resources (internet/network printers). Please correct me if wrong.

So the question is what do I need to achieve this? I've looked in to managed switched and 48 port ones are pretty damn expensive, do I need this? or, could I essentially get a 12/24 port and uplink another switch/hub/something without messing up the vlans?

Any help and advice on how to achieve this is greatly appreciated.


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If the companies care about security, they would need to use VLANs so that Company A's traffic doesn't end up at Company B's computer. But then again, it looks like they are sharing resources like the printer, so maybe security is not that important.

If you want to have one VLAN per company, you would at least need a number of ports equal to the number of companies plus one. The last port would go to the router and would be a tagged port that is on all VLANs. Then you would have one unmanaged switch/hub per company whose uplink feeds into the appropriate port on the switch.

Using VLANs will entain configuring the hosts from all these companies to be on different subnets so you will have to do some work on your DHCP server for giving out addresses on the appropriate subnet or renumber the customers' computers depending on whether or not they are configured to use DHCP.

The server/printer would have to be on a separate subnet and you'd have to route to them from each of these subnets. So you'd have to have a separate port on the router that connects to the "shared services" for all of the customers.


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You might try a used 3com 3300 switch. These come in 12 and 24 ports, are managed and programmable for vlans. They can be had pretty cheap on Ebay ($100 or so). Make sure you get one with the default or known passwords (needed to flash update or program). Some refurb companies also sell these for pretty good prices. Also, 3com has a neat free tool which maps your network and shows you the current state of things. This talks to their equipment to tell you very useful stuff (like traffic jams, etc).

3com Network Supervisor was discontinued, but is still available. The basic pkg is free, and the download gives you a trial on the extras.
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  1. Get a Nortel 425-24T switch. It is a managed Switch that can handle VLANs and Tagging.
  2. Create subnets on the Router for each company in the building.

Helper-address Helper-address (or whatever you need to do)

  1. Create the VLANs on the switch and plug 1 Ethernet cable for each company, into the switch, noting the port the cable is plugged into.

  1. Tag the incoming port from the router

  2. Tag each of the VLAN'd ports as well.

  1. Each port will feed a different company.

They will on their own section of the pipe and never touch each other yet share the same resorces. The online manual for the Nortel 425-24T explains the Tagging/VLAN process well.

Good luck

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