Spanning-Tree Interface States - Cisco ME 3400 Software Configuration Manual
Ethernet access switch
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Chapter 14
Configuring STP
Each Layer 2 interface on a switch using spanning tree exists in one of these states:
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.
•
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.
Note
A port participating in spanning tree 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
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From forwarding to disabled
•
Figure 14-1
Figure 14-1
Power-on
initialization
Blocking
state
Listening
state
Learning
state
Forwarding
state
When you power up the switch, spanning tree is enabled by default, and every NNI in the Cisco ME
switch (and every ENI on which STP has been enabled), as well as any other port in other switches in
the VLAN or network that are participating in spanning tree, goes through the blocking state and the
transitory states of listening and learning. Spanning tree stabilizes each interface at the forwarding or
blocking state.
OL-9639-07
On a Cisco ME switch, UNIs are always in the forwarding state. ENIs in the default STP mode
(disabled) are also in forwarding state, but you can enable STP on an ENI.
illustrates how an interface moves through the states.
Spanning-Tree Interface States
Disabled
state
Cisco ME 3400 Ethernet Access Switch Software Configuration Guide
Understanding Spanning-Tree Features
14-5
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