My understanding is that you are looking into a full-scale redesign of your network.
The most important factor in these cases (and especially when we are dealing with network as large as yours) is the network backbone and available equipment.
The Cisco 6500 series Catalyst switches provide a great amount of flexibility for your design, and I highly recommend you make use of its available features.
Firstly, you can surely survive without OSPF. Since your network backbone will consist of a number of switches connecting back to your core switch (6509), there is no need for OSPF. Static routing will do the job just fine, and once you have the network up and running without problems, you can consider adding more complexity (e.g OSPF) if you still believe its required.
Without having a full view of your network, available equipment and requirements, here’s what I suggest:
Each floor has a number of switches for workstation connectivity. These switches will connect to a central floor switch e.g 3560 or 3750 that should have at least two fiber optic links to your core switch, for redundancy. If you have switches available, you can even wire them directly to your core switch.
Without second thought, VLANs are a must for your network size – that’s one subnet per VLAN. Don’t think about it twice! If you include Per-VLAN Spanning Tree, you’ll be able to have the full benefits of Spanning Tree and VLANning.
In addition, it would be wise to also setup services such as VTP and VTP Pruning, to ensure your VLAN data is replicated correctly amongst all member switches and that trunks carry only the necessary data, depending on their location and configuration.
If you would like to read more on VLANs, Spanning Tree Protocol and how you should segment your network, you can browse through Searchnetworking.com’s ATE section and visit <a href=”http://www.firewall.cx”> www.Firewall.cx</a>.
Hope that helps!