Multiple Spanning Tree Protocol: Difference between revisions

Revision as of 20:49, 30 July 2024

Revision as of 19:39, 27 August 2024

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== History and motivation ==

It was originally defined in [[Institute of Electrical and Electronics Engineers|IEEE]] 802.1s as an amendment to [[IEEE 802.1Q|802.1Q]], 1998 edition and later merged into IEEE 802.1Q-2005 Standard, clearly defines an extension or an evolution of [[Radia Perlman]]'s Spanning Tree Protocol (STP) and the [[Spanning Tree Protocol#Rapid Spanning Tree Protocol|Rapid Spanning Tree Protocol]] (RSTP). It has some similarities with [[Cisco Systems]]' Multiple Instances Spanning Tree Protocol (MISTP), but there are some differences.

The original STP and RSTP work on the physical link level, preventing bridge loops when redundant paths are present. However, when a LAN is virtualized using VLAN trunking, each physical link represents multiple logical connections. Blocking a physical link blocks all its logical links and forces all traffic through the remaining physical links within the [[spanning tree]]. Redundant links cannot be utilized at all. Moreover, without careful network design, seemingly redundant links on the physical level may be used to connect ''different'' VLANs and blocking any of them may disconnect one or more VLANs, causing ''bad paths''.

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Its main function is enabling MSTP to select its root bridges for the proper CIST and each MSTI. MSTP includes all its spanning tree information in a single BPDU format. Not only does reduce the number of BPDUs required on a LANs to communicate spanning tree information for each VLAN, but it also ensures backward compatibility with RSTP (and in effect, classic STP too).

BPDUs' general format comprises a common generic portion ''-octets 1 to 36-'' that are based on those defined in IEEE Standard [[IEEE 802.1D|802.1D]], 2004,<ref>{{cite book|last = IEEE|first = Standard|title = IEEE Standard for Local and metropolitan area networks, Media Access Control (MAC) Bridges|publisher = IEEE Computer Society

|year = 2004|url = http://www.ccna-powertraining.de/wp-content/uploads/2014/10/802.1D-2004.pdf}}</ref> followed by components that are specific to CIST ''-octets 37 to 102.'' Components specific to each MSTI are added to this BPDUs data block.

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|doi = 10.17487/RFC2104

|url = https://tools.ietf.org/html/rfc2104

}}</ref> A 16B signature [[Hash-based message authentication code|HMAC]]-[[MD5|MD5 Algorithms]] created from the MST Configuration Table.<br />

This object is specific and unique of MSTP, neither STP or RSTP use it.

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* [[Media Redundancy Protocol]]

* [[Minimum spanning tree]]

* [[TRILL (computing)|TRILL]] (Transparent Interconnection of Lots of Links)

* [[Unidirectional Link Detection]]

* [[Virtual Link Trunking]]