Flat network or VLANs?

I would say a combination of the two, but much depends on what services your network is delivering. Core printing, file sharing, heavy duty Network Apps etc?

How are your remotes and mobiles connecting?
Permanent Wan links or RAS?

I would wager, not knowing any more info than you have provided, a combination of the two would be the best route, breaking out logical workgroups, with associated servers and network printers into vlan's.

The decision should be based on reducing the maximum amount of traffic across wan links, and regardless of the route you choose, is going to take some careful planning, much more than can be offered in response in this venue.

I definitely don't think you want a "flat" network with 2500 workstations. You'll need some sort of hierarchy, but it could be provided by segmenting rather than VLAN.

A VLAN is most appropriate in those situations where the business units don'tcorrespond with the physical locations. If all the finance people work in the same area, just create a segment. But if you want to create a Finance workgroup made up of all the people who work in finance at all locations, you'll need a VLAN.

paul

Let's take a look at performance, management, and security....

I have to assume that what you mean by a "flat" network is one where all 2500 workstations share the same IP address segment. This is certainly not advisable from a management perspective. When considering performance, modern switching technologies are more robust than routing so, performance on a LAN would not be a problem. However, if your network involves a WAN, you will certainly need to consider performance as well.

Keepin mind that a VLAN is virtual, riding on top of a physical LAN. Multiple VLANs sharing the same physical LAN don't improve performance at all. A VLAN is a great way to segment users for security and authentication purposes.

In your particular case, you will certainly want to route across the WAN to be able to control traffic and keep performance at a peak. On the LAN, you may want to segment into VLANs for management, monitoring, and/or security purposes. If you have a capable switch at the core of your network, performance should not be a problem and you should turn your efforts in the direction of management and security.

Nice answers, all. But I don't think the poster understands the issues and what VLANs are used for: Security, mainly.

What the poster really wants to know is: "Which is better a flat network or a segmented, hierarchal network?"

With 2500 users, the topology should most definately be segmented (dependant upon location)and have some kind of hierarchal switching/routing layers. Cisco has 3 layers in the switching models: Access>Distribution>Core layers. As an example, the users at the Access layers attache their PCs to low-end switches. These switches attach to higher-end L3 switches, where other L3 devices are attached, such as routers, and this is where L3 processes take place, such as routing and routing between VLANs. The Distribution layer switches then connect to the Core layer high-end switches where high-speed switching is performed on the backbone.

With such a network, you need to do some serious planning, perhaps with a consultant...