MSTP region
    An 
MSTP (Multiple Spanning Tree Protocol) region defines the logical boundary of the network. Interconnected
        bridges that have the same MSTP configuration are referred to as an MSTP region. Each MSTP
        region has a unique identifier, is bound together by one 
CIST (Common and Internal Spanning Tree)
        that spans the entire network, and contains from 0 to 64 MSTIs. A bridge participates in
        only one MSTP region at one time. An MSTP topology is individual MSTP regions connected
        either to the rest of the network with 802.1D and 802.1w bridges or to each
        other.