Multiple Spanning Tree Protocol: Difference between revisions

Revision as of 02:47, 11 October 2021

Revision as of 13:12, 8 February 2022

Line 96:

== Protocol Operation ==

MSTP configures for every VLAN a single spanning tree active topology in a manner that there's at least one data route between any two end stations, eliminating data loops. It specifies various "objects" allowing out the algorithm to operate in a proper way. The different bridges in the various VLANs start advertising their own configuration to other bridges using the MST Configuration Identifier in order to allocate frames with given VIDs (VLAN ID) to any of the different MSTI. A priority vector is utilized to construct the CIST, it connects all the bridges and LANs in a Bridged LAN and ensures that paths within each region are always preferred to paths outside the Region. Besides, there is a MSTI priority vector, this one compromises the necessary information to build up a deterministic and independently manageable active topology for any given MSTI within each region.

Additionally, comparisons and calculations done by each bridge select a CIST priority vector for each [[Port (computer networking)|Port]] (based on priority vectors, MST Configuration Identifiers and on an incremental Path Cost associated to each receiving port). This leads to one bridge been selected as the CIST Root of the Bridged LAN; then, a minimum cost path to the root is shifted out for each Bridge and LANs (thus preventing loops and ensuring full connectivity between VLANs). Subsequently, in each region, the bridge whose minimum cost path to the root doesn't pass through another bridge with the same MST Conf.ID will be identified as its Region's CIST Regional Root. Conversely, each Bridge whose minimum cost path to the Root is through a Bridge using the same MST Configuration Identifier is identified as being in the same MST Region as that Bridge.