Designing a gigabit backbone campus network. College have six buildings, each building contain 200 computers. In each building 200 computers connect to a centre switch using 100BaseT Full Duplex Ethernet link with a spanning tree topology. Centre switch connect to backbone router using a 1000BaseX Duplex Ethernet link. The backbone using a loop topology connect 6 routers next to each other with an OC48 link 2.4G full duplex link. Server farm located in one of those buildings.

Firstly in some design people using Cisco 12000 Series Routers (Cisco 12016). Are they too over on performance base on above requirements. If it is alright then which product in 12000 Series is suitable for my design? If 12000 Series is too good which result a bad cost-efficiency design then which series of Cisco router can I use, maybe even Cisco switch with routing function.

In future if the computer number in one building is doubled to 400. Then can I using the same topology add another 200 computers with a centre switch to the backbone router? (Two subnets connect to one router). Or I must buy another backbone router for the extra 200 computers.

If more redundancy links are required between the backbone routers. The could I have some suggest on how to deploy the redundancy links. How complex should I design the redundancy.( If too much redundancy then result money waste on interface cards)