Blocking State; Listening State; Learning State; Forwarding State - Cisco 2950G 24 - Catalyst Switch Software Configuration Manual
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- Migration manual (25 pages) ,
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Chapter 11
Configuring STP
Blocking State
A Layer 2 interface in the blocking state does not participate in frame forwarding. After initialization, a
BPDU is sent to each interface in the switch. A switch initially functions as the root until it exchanges
BPDUs with other switches. This exchange establishes which switch in the network is the root or root
switch. If there is only one switch 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 after switch
initialization.
An interface in the blocking state performs as follows:
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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 determines that the interface should participate in frame forwarding.
An interface in the listening state performs as follows:
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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 as follows:
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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 as follows:
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Discards frames received on the port
Discards frames switched from another interface for forwarding
Does not learn addresses
Receives BPDUs
Discards frames received on the port
Discards frames switched from another interface for forwarding
Does not learn addresses
Receives BPDUs
Discards frames received on the port
Discards frames switched from another interface for forwarding
Learns addresses
Receives BPDUs
Receives and forwards frames received on the port
Forwards frames switched from another port
Learns addresses
Receives BPDUs
Understanding Spanning-Tree Features
Catalyst 2950 Desktop Switch Software Configuration Guide
11-7
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