In this paper we present a study characterizing VLAN us- age in a large-sized campus network. Despite their extensive prevalence in enterprise and campus networks, the usage of VLANs has received little systematic treatment in the re- search community. Our study is conducted using a white- box approach, involving data such as router configuration files obtained from network operators, and through itera- tive interactions with them. Our study shows that the use of virtualization is prevalent to enable users belonging to physically disparate locations to be treated as a group. We demonstrate and characterize the performance inefficiencies resulting from virtualization. We show the inefficiencies are exacerbated by sub-optimal placement policies. We also dis- cuss potential sources of errors that may arise with configu- ration of VLANs, and demonstrate their prevalence in real configurations. We believe these results are a key step to- wards gaining deeper insights into operational practices in enterprise and campus networks, and the design of abstrac- tions to simplify management.
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