Multiple Spanning Tree Protocol: Difference between revisions

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=== Common and Internal Spanning Tree (CST/CIST) ===

[[File:CIST.png|thumb|CIST operates links between regions and to SST devices.]]

We can differenciatedifferentiate two kinds of conformated Spanning Trees into the different networks created by MSTP, these are:

* '''Common Spanning Tree (CST):''' Administers the connectivity among MST regions,[[Spanning Tree Protocol|STP]] [[Local area network|LANs]] and [[Spanning Tree Protocol#Rapid Spanning Tree Protocol|RSTP]] [[Local area network|LANs]] in a bridged network.

* '''Common Internal Spanning Tree (CIST):''' Identifies regions in a network and administers the CIST root bridge for the network, for each region and for each spanning tree instance in each region. It’s also the default spanning tree instance of MSTP so that any [[Virtual LAN|VLAN]] which isn’t a member of a particular [[Multiple Spanning Tree Protocol#Multiple Spanning Tree Instances .28MSTI.29|MSTI]], will be a member of the CIST. Furthermore, works as well as the spanning tree that runs between regions and between MST regions and Single Spanning Tree (SST) entities.

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{{Main article|Bridge Protocol Data Unit}}

Its main function is enabling MSTP to select its root bridges for the proper [[Multiple Spanning Tree Protocol#Common and Internal Spanning Tree .28CST.2FCIST.29|CIST]] and each [[Multiple Spanning Tree Protocol#Multiple Spanning Tree Instances .28MSTI.29|MSTI]]. MSTP includes all its spanning tree information in a single [[Bridge Protocol Data Unit|BPDU]] format. Not only does reduce the number of [[Bridge Protocol Data Unit|BPDUs]] required on a [[Local area network|LANs]] to communicate spanning tree information for each [[Virtual LAN|VLAN]], but it also ensures backward compatibility with [[Spanning Tree Protocol#Rapid Spanning Tree Protocol|RSTP]] (and in effect, classic [[Spanning Tree Protocol|STP]] too).

[[Bridge Protocol Data Unit|BPDUs']] general format comprises a common generic portion ''-octets 1 to 36-'' that are based on those defined in [[Institute of Electrical and Electronics Engineers|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 [[Multiple Spanning Tree Protocol#Common and Internal Spanning Tree .28CST.2FCIST.29|CIST]] ''-octets 37 to 102.'' Components specific to each [[Multiple Spanning Tree Protocol#Multiple Spanning Tree Instances .28MSTI.29|MSTI]] are added to this [[Bridge Protocol Data Unit|BPDUs]] data block.

<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 [[Multiple Spanning Tree Protocol#Common and Internal Spanning Tree .28CST.2FCIST.29|CIST]] ''-octets 37 to 102.'' Components specific to each [[Multiple Spanning Tree Protocol#Multiple Spanning Tree Instances .28MSTI.29|MSTI]] are added to this [[Bridge Protocol Data Unit|BPDUs]] data block.

[https://www.alliedtelesis.com/sites/default/files/stp_feature_config_guide.pdf BPDU table info] and [[Spanning Tree Protocol#Bridge_Protocol_Data_Unit_fields|STP BPDUs]] ''' show a deeper resume of the MSTP [[Bridge Protocol Data Unit|BPDU]] format''' and, besides, some additional information about how was this object structured in older or different versions of this protocol as [[Spanning Tree Protocol|STP]] and [[Spanning Tree Protocol#Rapid Spanning Tree Protocol|RSTP]], mantainingmaintaining its compatibility.

=== MSTP Configuration Identification ===