Parameters in planning for VLANs
What are the parameters in planning for VLANs? We have a network of 3000 users. What is the maximum number of VLANs we can have and how many hosts in each VLAN?
The main purpose of using VLANs is to take advantage of "locality" of communication -- that is, you have sets of users and servers that communicate mostly with each other. These sets create the logical partitions that you use to determine your VLANs. Performance improvements will be a function of how well segregated your traffic is by VLAN.
Another reason you might want to use VLANs is to provide improved security within your intranet. In this case, your VLANs represent distinct "trust boundaries" within your organization, and some form of access control is implemented in the routers.
Organizing your local environment around these factors should help define the size and membership in your VLANs.
This was first published in June 2003