Virtual LAN

networking Software defined groups of host on a localarea network (LAN) that communicate as if they were on the

same wire, even though they are physically on different LANsegments 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?].

(1995-04-03)