Rockwell Automation 1783-WAPxxx Stratix 5100 Wireless Access Point User Manual - Manual (Page 305)

Rockwell Automation Publication 1783-UM006A-EN-P - May 2014 305
Configuring Spanning Tree Protocol Chapter 9
Creating the Spanning-tree
Topology In this figure, bridge 4 is elected as the spanning-tree root because the priority of
all the access points is set to the default (32768) and bridge 4 has the lowest
MAC address. However, because of traffic patterns, number of forwarding
interfaces, or link types, bridge 4 might not be the ideal spanning-tree root. By
increasing the priority (lowering the numerical value) of the ideal bridge so that it
becomes the spanning-tree root, you force a spanning-tree recalculation to form a
new topology with the ideal bridge as the spanning-tree root.
Figure 89 - Spanning-tree Topology
Spanning-tree Interface States
Propagation delays can occur when protocol information passes through a
wireless LAN. As a result, topology changes can take place at different times and
at different places in the network. When an interface transitions directly from
nonparticipation in the spanning-tree topology to the forwarding state, it can
create temporary data loops. Interfaces must wait for new topology information
to propagate through the LAN before starting to forward frames. They must
allow the frame lifetime to expire for forwarded frames that have used the old
topology.
Each interface on a access point using spanning tree exists in one of these states:
Table 89 - Spanning Tree States
State Description
Blocking The interface does not participate in frame forwarding.
Listening The first transitional state after the blocking state when the spanning tree determines that
the interface can participate in frame forwarding.
Learning The interface prepares to participate in frame forwarding.
Forwarding The interface forwards frames.
Disabled The interface is not participating in spanning tree because of a shutdown port, no link on
the port, or no spanning-tree instance running on the port.
LAN segment A
LAN segment B
Bridge 1
Bridge 3
Bridge 2
Bridge 4
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