Spanning Tree

Each MSTI has a topology that is independent of every other. Data traffic originating from the same source and bound to the same destination but on different VLANs on different MSTIs may therefore travel a different path across the network.

IST

An MST region always defines an IST (Internal Spanning Tree). The IST spans the entire MST region, and carries all data traffic that is not specifically allocated (by VLAN) to a specific MSTI. The IST is always computed and is defined to be MSTI zero.

The IST is also the extension inside the MST region of the CIST (see below), which spans the entire bridged network, inside and outside of the MST region and all other RSTP and STP bridges, as well as any other MST regions.

CST

The CST (Common Spanning Tree) spans the entire bridged network, including MST regions and any connected STP or RSTP bridges. An MST region is seen by the CST as an individual bridge, with a single cost associated with its traversal.

CIST

The CIST (Common and Internal Spanning Tree) is the union of the CST and the ISTs in all MST regions. The CIST therefore spans the entire bridged network, reaching into each MST region via the latter’s IST to reach every bridge on the network.

5.2.2MSTP Bridge and Port Roles 5.2.2.1 Bridge Roles:

CIST Root

The CIST Root is the elected root bridge of the CIST (Common and Internal Spanning Tree), which spans all connected STP and RSTP bridges and MSTP regions.

CIST Regional Root

The root bridge of the IST within an MST region. The CIST Regional Root is the bridge within an MST region with the lowest cost path to the CIST Root. Note that the CIST Regional Root will be at the boundary of an MST region. Note also that it is possible for the CIST Regional Root to be the CIST Root.

MSTI Regional Root

The root bridge for an MSTI within an MST region. A root bridge is independently elected for each MSTI in an MST region.

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RuggedCom RS400 manual Mstp Bridge and Port Roles 5.2.2.1 Bridge Roles, Cist Root, Cist Regional Root, Msti Regional Root