3-7
Multiple Instance Spanning-Tree Operation
802.1s Multiple Spanning Tree Protocol (MSTP)
MSTI must initially exist in the IST instance of the same MST region. When
you assign a static VLAN to an MSTI, the switch removes the VLAN from
the IST instance. (Thus, you can assign a VLAN to only one MSTI in a given
region.) All VLANs in an MSTI operate as part of the same single spanning
tree topology. (The switch does not allow dynamic VLANs in an MSTI.)
Caution When you enable MSTP on the switch, the default MSTP spanning tree
configuration settings comply with the values recommended in the IEEE
802.1s Multiple Spanning Tree Protocol (MSTP) standard. Note that inappro-
priate changes to these settings can result in severely degraded network
performance. For this reason, HP strongly recommends that changing these
default settings be reserved only for experienced network administrators
who have a strong understanding of the IEEE 802.1D/w/s standards and
operation.
How MSTP Operates
In the factory default configuration, spanning tree operation is off. Also, the
switch retains its currently configured spanning tree parameter settings when
disabled. Thus, if you disable spanning tree, then later re-enable it, the param-
eter settings will be the same as before spanning tree was disabled. The switch
also includes a “Pending” feature that enables you to exchange MSTP config-
urations with a single command. (Refer to “Enabling an Entire MST Region at
Once or Exchanging One Region Configuration for Another” on page 3-42.)
Note The switch automatically senses port identity and type, and automatically
defines spanning-tree parameters for each type, as well as parameters that
apply across the switch. Although these parameters can be adjusted, HP
strongly recommends leaving these settings in their default configurations
unless the proposed changes have been supplied by an experienced network
administrator who has a strong understanding of the IEEE 802.1D/w/s
standards and operation.
MST Regions
All MSTP switches in a given region must be configured with the same VLANs.
Also, each MSTP switch within the same region must have the same VLAN-to-
instance assignments. (A VLAN can belong to only one instance within any
region.) Within a region:
■ All of the VLANs belonging to a given instance compose a single, active
spanning-tree topology for that instance.
■ Each instance operates independently of other regions.
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