STP Configuration
Designated Bridge
For a device, Designated Bridge is the device directly connected with this device and
responsible for forwarding BPDUs; For a LAN, Designated Bridge is the device responsible
for forwarding BPDUs to this LAN segment.
Designated Port
For a device, Designated Port is the port through which the designated bridge forwards
BPDUs to this device; For a LAN, Designated Port is the port through which the designated
bridge forwards BPDUs to this LAN segment.
Path cost
Path cost is a reference value used for link selection in STP. By calculating the path cost,
STP selects relatively “robust” links and blocks redundant links, and finally prunes the network
into loop-free tree structure.
21.1.4 Spanning-Tree Interface States
Each Layer 2 interface on a switch using spanning tree exists in one of these states：
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.
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 should participate in frame forwarding.
Learning
The interface prepares to participate in frame forwarding.
Forwarding
The interface forwards frames.
An interface moves through these states:
• From initialization to blocking
• From blocking to listening or to disabled
• From listening to learning or to disabled
• From learning to forwarding or to disabled
• From forwarding to disabled
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