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Spanning Tree Algorithm Configuration
3-95
3
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. This
creates one spanning tree instance for the entire network. If multiple VLANs are
implemented on a network, the path between specific VLAN members may be
inadvertently disabled to prevent network loops, thus isolating group members.
When operating multiple VLANs, we recommend selecting the MSTP option.
• 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.
Console#show spanning-tree 4-170
Spanning-tree information
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Spanning tree mode :MSTP
Spanning tree enable/disable :enable
Instance :0
Vlans configuration :1-4094
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
Max hops :20
Remaining hops :20
Designated Root :32768.0.0000ABCD0000
Current root port :1
Current root cost :200000
Number of topology changes :1
Last topology changes time (sec.):13380
Transmission limit :3
Path Cost Method :long
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