Owner's Manual

39
MST Instance Settings
Multiple Spanning Tree Protocol (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.