Using VLANs on a small network

I manage four Novell servers – two NW6.5sp2 and two NW5.0sp6a. These servers provide services to 5 buildings. These 5 buildings are part of a much larger campus encompassing approximately 40 buildings but I don’t service those other buildings. The network folks want to implement a VLAN on every floor of our buildings. We currently use Allied Telesyn Rapier 48 port 10/100 switches (AT-RP48) in all the buildings. In one building the first floor has 15 users and the 2nd has 50 users. In another building we have 40 users on one floor and another 40 in another. All other buildings have basically the same amount of users per floor. We really don’t have a large number of users per floor. Won’t implementing a VLAN per floor increase server latency? –Mercedes Elias

I manage four Novell servers – two NW6.5sp2 and two NW5.0sp6a. These servers provide services to 5 buildings. These 5 buildings are part of a much larger campus encompassing approximately 40 buildings but I don’t service those other buildings. The network folks want to implement a VLAN on every floor of our buildings. We currently use Allied Telesyn Rapier 48 port 10/100 switches (AT-RP48) in all the buildings. In one building the first floor has 15 users and the 2nd has 50 users. In another building we have 40 users on one floor and another 40 in another. All other buildings have basically the same amount of users per floor. We really don’t have a large number of users per floor. Won’t implementing a VLAN per floor increase server latency?

–Mercedes Elias

Even though your user count isn’t really high per floor, I like the idea of using one VLAN per floor. I wouldn’t expect much overhead from VLAN implementation – and the benefits you’ll get would far outweight any modest (if any) increases in latency.

You may have read about something called broadcast domain or collision domain. The smaller you can segment your network, the more you reduce the effect that broadcasts or collisions can have on the network. With VLANs, you are subdividing your network into smaller networks. This helps in identifying a problem PC more easily – for example, when it is the cause of a broadcast storm or gets infected with an mailer virus that turns it into a mini mail server and starts sending hello messages to everyone on the planet.

Especially when a new PC gets added that you didn’t know about, you can now go directly to a floor instead of having to interrogate your switches to find out what port the problem device is on. Since each VLAN will have a different subnet number, this will quickly tell you on what floor in what building that a particular system is located.

If a broadcast storm does take your network down, a VLAN may let you limit the effect of the storm to just one floor. VLANs let you decrease the number of potential collisions by segmenting the network into smaller pieces. And by reducing the number of potential problems, this could improve network reliability and so effectively make the network run faster over the long term.