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Cisco ME 3800X and 3600X Switch Software Configuration Guide
OL-23400-01
Chapter 13 Configuring STP
Understanding Spanning-Tree Features
Listening State
The listening state is the first state a Layer 2 interface enters after the blocking state. The interface enters
this state when the spanning tree decides that the interface should participate in frame forwarding.
An interface in the listening state performs these functions:
•
Discards frames received on the interface
•
Discards frames switched from another interface for forwarding
•
Does not learn addresses
•
Receives BPDUs
Learning State
A Layer 2 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 these functions:
•
Discards frames received on the interface
•
Discards frames switched from another interface for forwarding
•
Learns addresses
•
Receives BPDUs
Forwarding State
A Layer 2 interface in the forwarding state forwards frames. The interface enters the forwarding state
from the learning state.
An interface in the forwarding state performs these functions:
•
Receives and forwards frames received on the interface
•
Forwards frames switched from another interface
•
Learns addresses
•
Receives BPDUs
Disabled State
A Layer 2 interface in the disabled state does not participate in frame forwarding or in the spanning tree.
An interface in the disabled state is nonoperational.
A disabled interface performs these functions:
•
Discards frames received on the interface
•
Discards frames switched from another interface for forwarding
•
Does not learn addresses
•
Does not receive BPDUs
