March 11, 2004

VLANs on Linux

An introduction to VLANs and VLAN trunking, how Linux interacts with VLANs and how you might use them in networks.

To begin, we must have a more formal definition of what a LAN is. LAN stands for local area network. Hubs and switches usually are thought of as
participating in a single LAN. Normally, if you connect two computers to the same hub or switch, they are on the same LAN. Likewise, if you connect
two switches together, they are both on the same LAN.

A LAN includes all systems in the broadcast domain. That is, all of the systems on a single LAN receive a broadcast sent by any member of that LAN. By
this definition, a LAN is bordered by routers or other devices that operate at OSI Layer 3.

Now that we've defined a LAN, what is a VLAN? VLAN stands for virtual LAN. A single VLAN-capable switch is able to participate in multiple LANs at



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