In a Layer 2 network, the bridge with the lowest bridge ID becomes the CIST root bridge. The parameters (vectors) that define the root bridge include the following:
The CIST root bridge can be either inside or outside an MSTP region. The CIST root bridge is unique for all regions and non-MSTP bridges, regardless of its location.
For more information about configuring the bridge ID, see the configure stpd priority command.