Blocking State; Listening State; Learning State - Allen-Bradley Stratix 5100 User Manual

Blocking State

An interface in the blocking state does not participate in frame forwarding. After
initialization, a BPDU is sent to the access point's Ethernet and radio ports. A
access point initially functions as the spanning-tree root until it exchanges
BPDUs with other access points.
This exchange establishes the access point in the network that is the spanning-
tree root. If there is only one access point in the network, no exchange occurs, the
forward-delay timer expires, and the interfaces move to the listening state. An
interface always enters the blocking state when you enable STP.
An interface in the blocking state performs as follows:
• Discards frames received on the port
• Does not learn addresses
• Receives BPDUs
If a access point port is blocked, some broadcast or multicast packets can reach
IMPORTANT
a forwarding port on the access point and cause the bridging logic to switch
the blocked port into listening state momentarily before the packets are
dropped at the blocked port.

Listening State

The listening state is the first state an interface enters after the blocking state. The
interface enters this state when STP determines that the interface can participate
in frame forwarding.
An interface in the listening state performs as follows:
• Discards frames received on the port
• Does not learn addresses
• Receives BPDUs

Learning State

An interface in the learning state prepares to participate in frame forwarding.
The interface enters the learning state from the listening state.
An interface in the learning state performs as follows:
• Discards frames received on the port
• Learns addresses
• Receives BPDUs
Rockwell Automation Publication 1783-UM006A-EN-P - May 2014
Configuring Spanning Tree Protocol Chapter 9
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