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Spanning Tree Algorithm Configuration
3-79
CLI
– This command displays global STA settings, followed by settings for each port
.
Note: The current root port and current root cost display as zero when this device is not
connected to the network.
Configuring Global Settings
Global settings apply to the entire switch.
Command Usage
• Spanning Tree Protocol
Uses RSTP for the internal state machine, but sends only 802.1D BPDUs.
Rapid Spanning Tree Protocol
• RSTP supports connections to either STP or RSTP nodes by monitoring the
incoming protocol messages and dynamically adjusting the type of protocol
messages the RSTP node transmits, as described below:
- STP Mode – If the switch receives an 802.1D BPDU (i.e., STP BPDU) after a
port’s migration delay timer expires, the switch assumes it is connected to an
802.1D bridge and starts using only 802.1D BPDUs.
- RSTP Mode – If RSTP is using 802.1D BPDUs on a port and receives an
RSTP BPDU after the migration delay expires, RSTP restarts the migration
delay timer and begins using RSTP BPDUs on that port.
Command Attributes
Basic Configuration of Global Settings
• Spanning Tree State – Enables/disables STA on this switch. (Default:
Enabled)
• Spanning Tree Type – Specifies the type of spanning tree used on this switch:
- STP: Spanning Tree Protocol (IEEE 802.1D); i.e., when this option is
selected, the switch will use RSTP set to STP forced compatibility mode).
- RSTP: Rapid Spanning Tree (IEEE 802.1w); RSTP is the default.
Console#show spanning-tree 4-135
Spanning-tree information
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Spanning tree mode :RSTP
Spanning tree enable/disable :enable
Priority :32768
Bridge Hello Time (sec.) :2
Bridge Max Age (sec.) :20
Bridge Forward Delay (sec.) :15
Root Hello Time (sec.) :2
Root Max Age (sec.) :20
Root Forward Delay (sec.) :15
Designated Root :32768.000087654321
Current root port :1
Current root cost :200000
Number of topology changes :1
Last topology changes time (sec.):23771
Transmission limit :3
Path Cost Method :long
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