CIST regional root bridge

Within an MSTP (Multiple Spanning Tree Protocol) region, the bridge with the lowest path cost to the CIST (Common and Internal Spanning Tree) root bridge is the CIST regional root bridge If the CIST root bridge is inside an MSTP region, that same bridge is the CIST regional root for that region because it has the lowest path cost to the CIST root. If the CIST root bridge is outside an MSTP region, all regions connect to the CIST root through their respective CIST regional roots.