KB.15.15

Setting the maximum age of received STP information

Syntax:

spanning-tree maximum age

Sets the maximum age time for received STP information before it is discarded.

Default: 20 seconds

Manipulating the pending MSTP configuration

Syntax:

spanning-tree pending [ apply | config-name | config-revision | instance

| reset ]

Manipulates the pending MSTP configuration. The command is useful in test or

debug applications, and enables rapid reconfiguration of the switch for changes

in spanning tree operation.

apply Applies pending MSTP configuration (swaps active and

pending configurations).

config-name Sets the pending MST region configuration name. Default

is the switch's MAC address.

config-revision Sets the pending MST region configuration revision

number. Default is 0.

instance Change pending MST instance configuration.

reset Copies the active configuration to pending.

Setting the bridge priority for a region and determining the root switch

Syntax:

spanning-tree priority priority-multiplier

Every switch running an instance of MSTP has a Bridge Identifier, which is a unique

identifier that helps distinguish this switch from all others. The switch with the lowest

Bridge Identifier is elected as the root for the tree.

The Bridge Identifier is composed of a configurable priority component (2 bytes)

and the bridge's MAC address (6 bytes). The ability to change the priority

component provides flexibility in determining which switch will be the root for the

tree, regardless of its MAC address.

This command sets the switch (bridge) priority for the designated region in which

the switch resides. The switch compares this priority with the priorities of other

switches in the same region to determine the root switch for the region. The lower

the priority value, the higher the priority. If there is only one switch in the region,

then that switch is the root switch for the region. The root bridge in a region provides

the path to connected regions for the traffic in VLANs assigned to the region's IST

instance. Traffic in VLANs assigned to a numbered STP instance in a given region

moves to other regions through the root switch for that instance.

The priority range for an MSTP switch is 0-61440. However, this command specifies

the priority as a multiplier (0 - 15) of 4096. That is, when you specify a priority

multiplier value of 0 - 15, the actual priority assigned to the switch is:

(priority-multiplier) x 4096

For example, with 2 as the priority-multiplier on a given MSTP switch, the Switch

Priority setting is 8,192.

82 Multiple instance spanning tree operation