EnGenius EWS Series User Manual page 112

MST Instance Settings
Multiple Spanning Tree Protocol, or MSTP enables the grouping of multiple VLANs with the same
topology requirements into one Multiple Spanning Tree Instance (MSTI). MSTP then builds an Internal
Spanning Tree (IST) for the region containing commonly configured MSTP bridges. Instances are not
supported in STP or RSTP. Instead, they have the same spanning tree in common within the VLAN. MSTP
provides the capability to logically divide a Layer 2 network into regions. Every region can contain
multiple instances of spanning trees. In MSTP, all of the interconnected bridges that have the same MSTP
configuration comprise an MST region.
A Common Spanning Tree (CST) interconnects all adjacent MST regions and acts as a virtual bridge node
for communications between STP or RSTP nodes in the global network. MSTP connects all bridges and
LAN segments with a single Common and Internal Spanning Tree (CIST). The CIST is formed as a result of
the running spanning tree algorithm between switches that support STP, RSTP, and MSTP protocols.
Once you specify the VLANs you wish to include in a Multiple Spanning Tree Instance (MSTI), the
protocol will automatically build an MSTI tree to maintain connectivity among each of the VLANs. MSTP
maintains contact with the global network because each instance is treated as an RSTP node in the
Common Spanning Tree (CST).
Click the Edit button to configure the MST settings. Next, enter information for the VLAN List and choose
the priority you wish to use from the drop down list.
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