Inference of network-wide VLAN usage in small enterprise networks

Virtual local area networks (VLANs) are heavily utilized in enterprise networks to group hosts with common requirements together as if they were on the same LAN although they may be in separate physical locations. The key benefit of VLANs is its flexibility to allow any logical LAN to be implemented on any physical infrastructure. As a result, enterprise network administrators often use VLANs to group users and use the resulting grouping to control access to resources. Even in small enterprise networks such as the one we study in this paper, there are more than 50 VLANs in use. Despite their popularity, there has been little systematic work studying deployed VLANs and more importantly, understanding the traffic flow patterns inside these VLANs. In this paper, we develop simple light-weight techniques to map VLAN traffic as it flows across a network. The mapping results from our study can be used as a part of a tool to monitor VLAN usage and may be extended to applications in problem determination and VLAN configuration optimization.