14.
Multiple Spanning Tree Protocol (MSTP)
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port-priority <priority>
The port priority value, range is 0 (highest priority) to 255 (lowest priority).
The default is 128.
Example
device-name
(config)#
interface
ag2
device-name
(config-if AG02)#
mstp
0
port-priority
0 112 128 144 16 160 176 192 208 224 240 32 48 64 80 96
device-name
(config-if AG02)#
mstp
0
port-priority
208
device-name
(config-if AG02)#
NOTE
The port-priority command can be used on aggregate ports as well, as shown in the example
above. In such cases, the reference ag is included in the instance ID preceeding the ID
number
Setting the Path Cost
The
mstp path-cost
command, in Interface Configuration mode, configures the cost for an
MST instance. The
no
form of this command returns the interface to its default settings.
If a loop occurs, the MSTP uses the path cost when selecting an interface to place in the
forwarding state. A lower path cost represents higher-speed transmission
The default MSTP path cost value is derived from the link speed of an interface. If a loop
occurs, the MSTP uses cost when selecting an interface to put in the forwarding state. You
can assign lower cost values to interfaces that you want to be selected first and higher cost
values that you want to interfaces to be selected last. If all interfaces have the same cost value,
the MSTP puts the interface with the lowest interface number in the forwarding state and
blocks the other interfaces.
The default value is derived from the link speed of the interface. Table 14-3 displays the
default value calculated from the media speed of the interface.
Command Syntax
device-name
(config-if
UU/SS/PP
)#
mstp
<
instance-id
>
path-cost
<1-200000000>
device-name
(config-if
UU/SS/PP
)#
no mstp
<
instance-id
>
path-cost
Argument Description
instance-id
The MST instance ID, the range is 0 to 15.
<1-200000000>
The cost value, in the range <1-200000000>.
Example
device-name
(config)#
interface
ag2
device-name
(config-if AG02)#
mstp
0
path-cost
1
device-name(
config-if AG02)#
NOTE
The
mstp path-cost
command can be used on aggregate ports as well, as shown in the
example above. In such cases, the reference ag is included in the instance ID preceeding the
ID number