subnetting

It all depends on the nature of the traffic. If these are all user stations, I have seen many times where a /22 is used (1000+ addresses), and 4-500 are active during regular usage. If its a mixed use vlan with real-time traffic (such as video or voice, which would not be good architecture anyway), then subnetting to smaller subnets makes more sense. In short, 8 segments for 50 nodes each is overkill. I would personally not do smaller than /25, and /24 in most cases, unless of course the network is a retail or small site network which will never get larger than that space, or there are special vlan or traffic requirements. When you are talking modern gig speed networks, broadcast traffic is minimal unless you have an issue (ie bad worm or virus), or a network design problem.

There is no drawback to having too many subnets when routing with a 6500!!!! Layer 2 switching is not any faster than layer 3 switching and smaller subnets means a smaller broadcast domain. If you are running windows, than smaller broadcast domains are good because windows workstations send out quite a bit of broadcast traffic.

I never ever, ever use subnets bigger than a /24, and most subnets usually have an average of only about 60 workstations. On my network, each and every wiring closet has its own subnet, plus a voice subnet if it is a VoIP is being used.

The speed of the interface has nothing to do with the amount of broadcast traffic, that is a function of the number of devices in the broadcast domain. Each and every broadcast packet is sent to, and processed by, every device in the broadcast domain.

I agree, but in the days of 10/half interfaces, broadcast could easily overwhelm a link or subnet. Today, it would take one hell of a broadcast storm to overwhelm a modern backbone or LAN link. While I don't disagree with your subnet solution (can't really go wrong here, and have to design to your requirements), my experience is in two global Fortune 50 companies, and when you have dozens of datacenters, subnetting like that adds up quick on wasted addresses. That being said, I would not go larger than a /22. And, always subnet real time traffic if possible, particularly VoIP since the requirements/ segmentation work nicely.

I should also qualify that this entire discussion assumes centralized layer 2, which in itself is becoming a legacy design for very large networks. Distributed layer 3 is not necessarily cheap, but is feasible in most l3 switches today, and can help alleviate backbone traffic, broadcast traffic, and inter vlan routing since subnets are local to switch pairs only.