Allied Telesis SwitchBlade x3100 Series Manual page 401

Multiple Spanning Tree Protocol (MSTP)
4.5.8.1 MTSP Region
When a set of switches have the same MSTI configuration (meaning the set of switches have the same MSTIs
and their VLAN associations), these switches can make an MSTP region. This allows the group of switches to
be placed under a common administration; the region appears as one large bridge to the rest of the network
spanning tree (i.e. the CIST). Since there is one overall network instance, which connects all the regions, block-
ing on boundary ports would occur so that there would be no loops into and out of the MST Region. Refer to
the following figure.
One feature, Cisco Compatible STP Mode, allows the Allied Telesis SBx3112 to participate in the same
Note:
MSTP region with one or more adjacent Cisco bridges that do not meet the 802.1s MST standard.
To form an MSTP Region, all bridges that make up the region must share these attributes:
MSTP Instances
•
VLANs associated with these instances
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MSTP Region Name
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MSTP Region Revision Level
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Refer to Figure 4-8, which shows the MST Region as part of the larger CIST. The CIST represents a spanning
tree outside the MST region, but also has a spanning tree inside the region (the IST), and can carry all VLAN
traffic outside the MST region.
Note that it is not required that VLANs are configured on all the ports (interfaces), although it is necessary if
the user wishes traffic for a specific VLAN (which is part of an Instance) to be carried over that port. Not con-
figuring VLANs on the port can be useful in the following scenarios:
The user wishes to block VLAN traffic without changing the existing spanning tree
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As the MST Region is created, no loops are created.
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Software Reference for SwitchBlade x3100 Series Switches (Layer Two Switching)
Introduction
4-81