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8
S
T
P
PANNING
REE
ROTOCOL
W
S
IRELESS
This chapter describes wireless settings on the access point. It includes the
following sections:
◆
"Spanning Tree Protocol (STP)" on page 82
"Authentication" on page 85
◆
"Radio Settings" on page 89
◆
"Virtual Access Points (VAPs)" on page 93
◆
"QoS" on page 99
◆
(STP)
The Spanning Tree Protocol (STP) can be used to detect and disable
network loops, and to provide backup links between switches, bridges or
routers. This allows the wireless bridge to interact with other bridging
devices (that is, an STP-compliant switch, bridge or router) in your network
to ensure that only one route exists between any two stations on the
network, and provide backup links which automatically take over when a
primary link goes down.
STP uses a distributed algorithm to select a bridging device (STP-compliant
switch, bridge or router) that serves as the root of the spanning tree
network. It selects a root port on each bridging device (except for the root
device) which incurs the lowest path cost when forwarding a packet from
that device to the root device. Then it selects a designated bridging device
from each LAN which incurs the lowest path cost when forwarding a packet
from that LAN to the root device. All ports connected to designated
bridging devices are assigned as designated ports. After determining the
lowest cost spanning tree, it enables all root ports and designated ports,
and disables all other ports. Network packets are therefore only forwarded
between root ports and designated ports, eliminating any possible network
loops.
Once a stable network topology has been established, all bridges listen for
Hello BPDUs (Bridge Protocol Data Units) transmitted from the root bridge.
If a bridge does not get a Hello BPDU after a predefined interval (Maximum
Age), the bridge assumes that the link to the root bridge is down. This
bridge will then initiate negotiations with other bridges to reconfigure the
network to reestablish a valid network topology.
– 82 –
ETTINGS
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