14.
Multiple Spanning Tree Protocol (MSTP)
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topology for frames classified as belonging to VLANs that are mapped to the MSTI by the
MST Configuration Table used by the MST Bridges of each MST Region. The IST is
numbered 0, and the MSTIs are numbered 1, 2, 3, and so on. Each MSTI is local to the MST
region and is independent of MSTIs in the other regions, even if the MST regions are
interconnected.
Feature Overview
Definitions and Acronyms
Table 14-1 defines terms that are used in this document and lists their acronyms as specified
in the IEEE 802.1s standard.
Table 14-1 Definitions and Acronyms of Terms
T e r m A c r o n y m
D e f i n i t i o n
Boundary Port
--
A Bridge Port attaching an MST Bridge to a LAN that is
in another region.
Common Spanning
Tree
CST
The single Spanning Tree calculated by STP and RSTP,
and by MSTP to connect MST Regions.
Common and
Internal Spanning
Tree
CIST
A collection of the ISTs in each MST region, and the
common spanning tree (CST) that interconnects the
MST regions.
The CIST is calculated by MSTP to ensure that all LANs
in the Bridged Local Area Network are simply and fully
connected.
Internal Spanning
Tree
IST
The connectivity provided by the CIST within a given
MST Region.
The IST is the first MSTI in the region, numbered as
MSTI0, and it exists by default and cannot be removed.
All other MST instances are numbered from 1 to 15.
Multiple Spanning
Tree Instance
MSTI
One of a number of Spanning Trees calculated by MSTP
within an MST Region. The MSTI is defined per VLAN
group, and is designed to provide a simply and fully
connected active topology for frames classified as
belonging to VLANs that are mapped to the MSTI by the
MST Configuration Table that is used by the MST
Bridges of that MST Region.
MST Configuration
Table
--
A configurable table that allocates each and every
possible VLAN to the Common Spanning Tree or a
specific Multiple Spanning Tree Instance.
MST Bridge
--
A Bridge capable of supporting the CST, and one or
more MSTIs, and of selectively mapping frames
classified in any given VLAN to the CST or a given MSTI.
MST Configuration
Identifier
MCID
A name for, revision level, and a summary of a given
allocation of VLANs to Spanning Trees.
NOTE—Each MST Bridge uses a single MST
Configuration Table and Configuration Identifier.