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V
LAN
IRTUAL
S
The following figure gives an illustration of how the Spanning Tree
Algorithm assigns bridging device ports.
Root Bridging
Device
Designated Port
Designated Port
Root Port
Root Port
Blocking
Designated Port
Designated Port
Designated Port
Root Port
Root Port
Root Port
Virtual LANs
Switches do not inherently support broadcast domains, which can
lead to broadcast storms in large networks that handle a lot of
traffic, such as NetBuei or IPX. In conventional networks with
routers, broadcast traffic is split up into separate domains to
confine this traffic to the originating group and provide a much
cleaner network environment. Instead of using physically separate
subnets which are linked by traditionally slow routers, this switch
creates segregated broadcast domains based on easily configurable
VLANs, and then links these VLANs as required with wire-speed
routing.
An IEEE 802.1Q VLAN is a group of ports that can be located
anywhere in the network, but communicate as though they belong
to the same physical segment. VLANs help to simplify network
management by allowing you to move devices to a new VLAN
without having to change any physical connections. VLANs can be
easily organized to reflect departmental groups (such as Marketing
or R&D), usage groups (such as e-mail), or multicast groups (used
for multimedia applications such as videoconferencing).
4-5
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