When designing a Wide Area Network (WAN) there are some considerations to make regarding network management, efficiency, and performance. The network diagram below has been successful for many NewNet 66 schools. This design is based on the products noted in the diagram but will work with many other types of routers, switches, and firewalls providing they have the ability to route.
Questions you might have:
~ Why route between the buildings? In large networks with say over 200 network hosts (PCs, printers, etc.) with multiple buildings, the broadcast domain starts becoming an issue. Additionally, many viruses and worms won't traverse a routed network so when the bad stuff gets in then it may only affect a particular building, not the entire network.
~ Why put public IPs on the switches? Putting public IPs on the "core" network devices allows for easy remote management. This can be done in other ways but in this example it makes it easier to understand.
~ What are Vlans? Think of a Vlan (Virtual Local Area Network) as a "virtual router" in this case. Each switch has the ability to route networks between the buildings so it must function as a router. In it's basic functionality, a router does nothing more that allow two or more networks to talk to each other. The Extreme Networks switches in this example route at "wire speed" so they are extremely fast and do not degrade network performance.
~ Why would I want multiple networks, this puts more "hops" in my wide area network? We here this all the time and this thinking is simply NOT correct. For example: Many school network support folks are told by others that they must reduce the number of network hops so that H.323 distance education classes will work properly. If you design your network correctly and use quality switches and routers, then Video conferencing is not an issue. Additionally you can implement QoS (quality of service) profiles in the switches that will assign priorities to your traffic like VoIP or H.323.
Things you should not do:
~ Don't use a subnet mask like 255.255.0.0 in your local network if possible. This subnet mask allows for 65,024 hosts or network devices. This is a very large broadcast domain and will cause you pain.
~ Don't use older hubs and switches. Purchase quality switches that are capable of routing. Plan on spending some fairly big bucks here. Purchasing "managed" switches allows you to look inside the switch and view activity and other statistics on each port.
You want to "manage" your network. Don't let the network manage you!
Building a Routed Network