Virtual LAN
<networking> Software defined groups of
host on a
local area network (LAN) that communicate as if they were on the same wire, even though they are physically on different LAN segments throughout a site.
To define a virtual LAN, the
network administrator uses a virtual LAN management utility to establish membersip rules that determine which hostss are in a specific virtual LAN.
Many models may exist but two seem to dominate:
(1) Vitual Segment (or Port-Group) Virtual LAN.
These are switched at the
data link layer (
OSI layer 2).
Virtual segments turn an arbitrary number of physical segments into a single virtual segment that funtions as a self-contained traffic domain.
(2) Virtual Subnet Virtual LAN: These are switched at the
Network Layer (
OSI layer 3).
Subnet-oriented virtual LANs are based on
subnet addresses used by
IP,
IPX, and other
network layer protocols to normally identify physical networks.
Administrators assign one subnet address to a number of switch
ports (which may be on different switches and over a backbone).
Once identified as a virtual subnet, the selected LANs function as a bridge group - traffic is bridged at Layer 2 within the virtual subnet and routed at Layer 3 between virtual subnets.
["The many faces of virtual LANs", Steven King, Network World, 1994/5?].
