Dell PowerConnect 5524P User Manual page 430

instance is associated with the Layer 2 domain on which it performs loop
detection and mitigation. This enables a port to be stopped in one
instance, such as traffic from VLAN A that is causing a loop, while traffic
can remain active in another domain where no loop was seen, such as on
VLAN B.
MSTP provides full connectivity for packets allocated to any VLAN, and
transmits packets assigned to various VLANs, through different multiple
spanning tree (MST) regions.
MST regions act as a single bridge.
For more information on configuring Multiple STP, see "Multiple
Spanning Tree" on page 448.
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Dell PowerConnect 55xx Systems User Guide