Configuration Guide 202
Configuring Spanning Tree Spanning Tree
In RSTP/MSTP, the alternate port is the backup for the root port. It is blocked when the root
port works normally. Once the root port fails, the alternate port will become the new root
port.
In STP, the alternate port is always blocked.
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Backup Port
If a port is not selected as the designated port for it receives better BPDUs from the switch
it belongs to, it will become an backup port.
In RSTP/MSTP, the backup port is the backup for the designated port. It is blocked when
the designated port works normally. Once the root port fails, the backup port will become
the new designated port.
In STP, the backup port is always blocked.
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Disable Port
The disconnected port with spanning tree function enabled .
Port Status
Generally, in STP, the port status includes: Blocking, Listening, Learning, Forwarding and
Disabled.
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Blocking
In this status, the port receives and sends BPDUs. The other packets are dropped.
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Listening
In this status, the port receives and sends BPDUs. The other packets are dropped.
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Learning
In this status, the port receives and sends BPDUs. It also receives the other user packets to
update its MAC address table, but doesn’t forward them.
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Forwarding
In this status, the port receives and sends BPDUs. It also receives the other user packets to
update its MAC address table, and forwards them.
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Disabled
In this status, the port is not participating in the spanning tree, and drops all the packets it
receives.
In RSTP/MSTP, the port status includes: Discarding, Learning and Forwarding. The
Discarding status is the grouping of STP’s Blocking, Listening and Disabled, and the
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