Virtual Local Area Networks

Abstract

With the availability of so many high-density, wire-speed Layer 3 switches, why would a network administrator choose to implement Virtual LANs (VLANs) today? The first (and most obvious) answer is cost. Layer 3 switches cost more than Layer 2 switches, and usually have less density, making them a natural fit at the very core of the network, leaving Layer 2 switches to handle Distribution Layer aggregation of wiring closet switches or Data Center switching. Layer 2 switches are often much simpler to implement, and can be implemented with less technical difficulty than routing. VLANs have also recently been reborn in Metropolitan Area Networks (MANs) based upon Ethernet technology as a Virtual Private Networking (VPN) solution. VLANs are now a required feature in any switched LAN solution. The increasing capacity and performance of switches has enabled users to dedicate switch ports to every user on the network, increasing the need for control over broadcast and multicasts throughout the network. To best understand VLANs, it is useful to study how networks evolved into needing VLANs.