These are special purpose devices and computers that just transfer messages from
one network to another. Before we look deep into the topic Virtual LAN's, let
us see the basic devices used in the network backbone. They are
:-Bridges operate at the data link layer. They connect two LAN segments that
use the same data link and network protocol.
:-Like bridges, switches operate at the data link layer. Switches connect two
or more computers or network segments that use the same data link and network
ROUTERS :-Routers operate
at the network layer. Routers connect two or more LANs that use the same or different
data link protocols, but the same both the basic system interconnection and the
necessary translation between the protocols in both directions.
:- Physical layer devices that are really just multiple port repeaters. When an
electronic digital signal is received on a port, the signal is reampli-fied or
regenerated and forwarded out all segments except the segment from which the signal
In a broadcast environment,
a broadcast is sent out by a host on a single segment would propagate to all segments,
saturating the bandwidth of the entire network. Also, without forcing some method
of checking at an upper layer, all devices in the broadcast domain would be able
to communicate via Layer 2.This severely limits the amount of security that could
be enforced on the network. Before the introduction of switches and VLANs, networks
were divided into multiple broadcast domains by connectivity through a router
.Because routers do not forward broadcasts, each interface is in a different broadcast
domain. Each segment is an individual IP subnet and regardless of a workstation's
function, its subnet is defined by its physical location.
group of devices on one or more logically segmented LANs (configured by use of
software), enabling devices to communicate as if attached to the same physical
medium, when they are actually located on numerous different LAN segments. VLANs
are based on logical instead of physical connections and thus are tremendously
A VLAN is logical broadcast
domain that can span multiple physical LAN segments .A VLAN can be designed to
provide independent broadcast domains for station logically segmented by functions,
project teams, or applications without regard to the physical location of users.
Each switch port can only be assigned to only one VLAN. Ports in a VLAN share
broadcasts. Ports that do not belong to the same VLAN do not share
This control of broadcast improves the network's overall performance.
enable switches to create multiple broadcast domains within a switched network.
Any user in this VLAN would receive a broadcast from any other member of the VLAN;
users of other VLANs would not receive these broadcasts. Each of the users in
a given VLAN would also be in the same IP subnet.
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