Quick Reference Guide
154 | Spanning Tree
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The following commands influence which switch becomes the root bridge and the role of a port in the
spanning tree:
Example of influencing the spanning tree configuration
This example shows the use of the spanning-tree mst port-priority command to influence the assignment of
the forwarding port in a spanning tree. Figure 10-114 shows that port 10 has the forwarding role in the
spanning tree. After executing
spanning-tree mst 5 port-priority 240, Figure 10-115 on page 156 shows that
port 11 now has the forwarding role. :
Figure 10-114. Using the show spanning-tree mst port summary Command
Command Syntax Command Mode Purpose
spanning-tree msti {0 {cost 1-200000000
| external-cost 1-200000000 | 0-240
} |
1-63 {cost 1-200000000 | priority 0-240}}
Interface Config
To influence the role of the selected port in the
spanning tree:
• Lowering the cost value reduces the path cost
of the selected port, thereby increasing the
likelihood that it will be selected as the root
port.
• Lowering the priority value reduces the port
priority of the selected port, thereby
increasing the likelihood that its paired port
will be selected as the root port.
spanning-tree msti priority mstid 0–61440
Global Config Influence the selection of the root bridge by setting
the bridge priority.
The instance
mstid is a number in the range 0-63 that
corresponds to the desired existing multiple spanning
tree instance.
0–61440 is the priority value, representing a
range of 0 to 61440, in increments of 4096.
Force10 #show spanning-tree mst port summary 5 all
STP STP Port
Interface Mode Type State Role
--------- -------- ------- ----------------- ----------
1/0/1 Enabled Disabled Disabled
1/0/2 Enabled Disabled Disabled
1/0/3 Enabled Disabled Disabled
1/0/4 Enabled Disabled Disabled
1/0/5 Enabled Disabled Disabled
1/0/6 Enabled Disabled Disabled
1/0/7 Enabled Disabled Disabled
1/0/8 Enabled Disabled Disabled
1/0/9 Enabled Disabled Disabled
1/0/10 Enabled Forwarding Designated
1/0/11 Enabled Discarding Backup
1/0/12 Enabled Disabled Disabled
1/0/13 Enabled Disabled Disabled
1/0/14 Enabled Disabled Disabled
1/0/15 Enabled Disabled Disabled
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