Different people use different guidelines but a commonly accepted size is a class C network ie /24. A lot does depend on the applications you are running on the vlans ie. if they use a lot of broadcasts to function then you may need a smaller size.
We use /25's per vlan where i work which gives 126 useable IP addresses.
The basic risk of too big a broadcast domain is that your clients spend too much time and resources processing broadcast traffic that may or may not be for them.
Just to add a little more t Jn's comment, keeping the subnet size small also helps should you have problems along the lines of code red or SQL slammer. Once a subet is identified as having an infected device, shutting down the VLAN as the first step before locating the infected device has a lower impact on other users - you are less likely to get grief for taking 70 users offline than if you took 400 users out for a single infected device.
Going for smaller subnets also makes the use of L3 links between switches potentially more practical.
We are pleased to announce availability of Beta software for 16.6.3.
16.6.3 will be the second rebuild on the 16.6 release train targeted
towards Catalyst 9500/9400/9300/3850/3650 switching platforms. We are
looking for early feedback from customers befor...
Introduction Featured Speakers Luis Espejel is the Telecommunications
Manager of IENova, an Oil & Gas company. Currently he works with Cisco
IOS® and Cisco IOS XE platforms, and NX to some extent. He has also
worked as a Senior Engineer with the Routing P...
In this session you can learn more about Layer 3 multicast and the best
practices to identify possible threats and take security measures. It
provides an overview of basic multicast, the best security practices for
use of this technology, and recommendati...