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{{IPstack}}
{{commons category|MSTP}}
The '''''Multiple Spanning Tree Protocol''''' (MSTP) and [[
Moreover, MSTP allows frames/packets assigned to different [[Virtual LAN|VLANs]] to follow separate paths, each based on an independent [[
== History ==
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 [[Institute of Electrical and Electronics Engineers|IEEE]] [[IEEE 802.1Q|802.1Q-2005 Standard]], clearly defines an extension or an evolution of [[Radia Perlman|Radia Perlman’s]] [[
If there is only one [[Virtual LAN|VLAN]] in the network, single (traditional) [[
== Main Entities ==
=== Multiple Spanning Tree Instances (MSTI) ===
[[File:MSTI.png|thumb|Different Spanning trees created by different MSTIs on the same physical layout.]]
As MSTP enables grouping and mapping [[Virtual LAN|VLANs]] into different spanning tree instances, there’s an urge of determining a group or set of [[Virtual LAN|VLANs]], which are all using the same spanning tree, this is what we come to know as a MSTI. <br />
Each instance defines a single forwarding topology for an exclusive set of [[Virtual LAN|VLANs]], by contrast, [[
|last = packard
|first = Hewlett
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|year = 2006
|url = ftp://ftp.hp.com/pub/networking/software/2900-AdvTrafficMgmt-Aug2006-59916197-Chap04.pdf
}}</ref>
* '''Internal Spanning-Tree Instance (IST)''': Default spanning tree instance in any MST region.All [[Virtual LAN|VLANs]] in this IST instance conform a '''single''' spanning tree [[Topology#
* '''Multiple Spanning Tree Instance (MSTI)''': Unlike IST, this kind of instance comprises all static [[Virtual LAN|VLANs]] specifically assigned to it and at least, must include one [[Virtual LAN|VLAN]].
''While each MSTI can have multiple [[Virtual LAN|VLANs]], each [[Virtual LAN|VLAN]] can be associated with only one MSTI.''
=== MSTP Regions ===
[[File:MST Region.png|thumb|MSTIs in different regions.]]
A set of interconnected switches that must have configured the same [[Virtual LAN|VLANs]] and [[
* '''MST Configuration Name'''
* '''Revision Level'''
* '''Configuration Digest:''' Mapping of which [[Virtual LAN|VLAN]] are mapped to which MST instances.
An [[
=== Common and Internal Spanning Tree (CST/CIST) ===
[[File:CIST.png|thumb|CIST operates links between regions and to SST devices.]]
We can differenciate 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,[[
* '''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 [[
The role of the Common Spanning Tree (CST) in a network, and the Common and Internal Spanning Tree (CIST) configured on each device, is to prevent loops within a wider network that may span more than one [[
=== MSTP Bridge Protocol Data Units (BPDU) ===
{{Main article|Bridge Protocol Data Unit}}
Its main function is enabling MSTP to select its root bridges for the proper [[
[[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
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|url = http://www.ccna-powertraining.de/wp-content/uploads/2014/10/802.1D-2004.pdf
}}</ref>
, followed by components that are specific to [[
[https://www.alliedtelesis.com/sites/default/files/stp_feature_config_guide.pdf BPDU table info] and [https://en.wikipedia.org/wiki/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 [[
=== MSTP Configuration Identification ===
In case there is an allocation of [[
* '''Configuration Identifier Format Selector:''' Indicates the use which is going to be given to the following components.
* '''Configuration Name'''<ref>{{cite book
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|year = 1998
|url = https://tools.ietf.org/html/rfc2271
}}</ref>
|last = IETF
|first = RFC
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|year = 1999
|url = https://tools.ietf.org/html/rfc2571
}}</ref>
|last = IETF
|first = RFC
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|year = 1997
|url = https://tools.ietf.org/html/rfc2104
}}</ref>
|last = IETF
|first = RFC
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|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 [[
== Protocol Operation ==
MSTP configures for every [[Virtual LAN|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 [[Virtual LAN|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 [[
Additionally, comparisons and calculations done by each bridge select a [[
In summary, MSTP encodes some additional information in its [[Bridge Protocol Data Unit|BPDU]] regarding region information and configuration, each of these messages conveys the spanning tree information for each instance. Each instance can be assigned several configured [[Virtual LAN|VLANs]], frames (packets) assigned to these [[Virtual LAN|VLANs]] operate in this spanning tree instance whenever they are inside the MST region. To avoid conveying their entire [[Virtual LAN|VLAN]] to spanning tree mapping in each [[Bridge Protocol Data Unit|BPDU]], bridges encode an MD5 digest of their [[Virtual LAN|VLAN]] to instance table in the MSTP [[Bridge Protocol Data Unit|BPDU]]. This digest is then used by other MSTP bridges, along with other administratively configured values, to determine if the neighboring bridge is in the same MST region as itself.
== Port Roles ==
=== Common Internal Spanning Tree Ports ===
* '''Root:''' Provides the minimum cost path from the Bridge to the [[
* '''Designated:''' Provides the least cost path from the attached [[Local area network|LAN]] through the Bridge to the [[
* '''Alternate or Backup:''' Provides connectivity if other Bridges, Bridges [[Port (computer networking)|Ports]] or [[Local area network|LANs]] fail or are erased.
=== Multiple Spanning Tree Instance Ports ===
* '''Root:''' Provides the minimum cost path from the Bridge to the [[
* '''Designated:''' Provides the least cost path from the attached [[Local area network|LANs]] through the Bridge to the Regional Root.
* '''Master:''' Provides connectivity from the Region to a [[
* '''Alternate or Backup:''' Provides connectivity if other Bridges, Bridges [[Port (computer networking)|Ports]] or [[Local area network|LANs]] fail or are erased.
== RSTP compatibility ==
MSTP is designed to be [[
Both protocols have in common various issues such as: the selection of the [[
Into the bargain, they also share some problems as, for instance: MSTP can’t protect against temporary loops caused by the inter-connection of two [[Local area network|LANs]] segments by devices other than the Bridges that operate invisibly with respect to support of the Bridges’ [[MAC address|MAC]] Internal Sublayer Service.
For all the above, it can be concluded that MSTP is fully compatible with [[
== Protocol Configuration ==
This section is mainly oriented to provide any user a proper manner of configuring a MSTP network over [[Cisco Systems|Cisco]] devices.
=== Before Configuring MSTP ===
Be sure of having configured [[Virtual LAN|VLANs]] and having associated them with switch ports, afterwards determine: [[
=== Configuration guidelines for MSTP ===
[[File:MSTP config.png|thumb|Simple network topology for MSTP trials.]]
# Switches must have the same MST configuration identification elements (region name, revision level and [[Virtual LAN|VLAN]] to [[
# Common and Internal Spanning Tree (CIST) is the default spanning tree instance for MSTP. This means that all [[Virtual LAN|VLANs]] that are not explicitly configured into another [[
# The software supports a single instance of the MSTP Algorithm consisting of the [[
A [[Virtual LAN|VLAN]] can only be mapped to one [[
An example of how to configure a simple, three switch SMTP topology wherein a layer-two access switch carries four [[Virtual LAN|VLANs]] and has two uplinks to two distribution switches, can be found here: [http://packetlife.net/blog/2010/apr/26/multiple-spanning-tree-mst/ MSTP Configuration Guide]<br />
A good configuration view, from the aboved-mentioned example shall be:
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---------------- ---- --- --------- -------- --------------------------------
Fa0/13 Altn BLK 200000 128.13 P2p
Fa0/16 Root FWD 200000 128.16 P2p
== Extensions ==
=== Alternative Multiple Spanning Tree Protocol (AMSTP) ===
The first skel of this protocol was proposed in
|last = Ibáñez, García, Azcorra
|first = Guillermo, Alberto, Arturo
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|year = 2002
|url = http://e-archivo.uc3m.es/bitstream/handle/10016/2791/amstp-2004.pdf?sequence=1
}}</ref>
==== Protocol Operation ====
To set up these trees, AMSTP relies in one basic tree which will be used to obtain instances (named Alternate Multiple Spanning Tree Instances – AMSTI), until one of them is built per switch for the network. The process applied to build up the main/basic tree is the same as in [[
==== BPDUs ====
{{Main article|Bridge Protocol Data Unit}}
AMSTP [[Bridge Protocol Data Unit|BPDUs]] use the same local multicast protocol addresses than [[
=== ABRIDGES ===
This protocol, developed in <ref>{{cite book
|last = Ibáñez, García, Azcorra, Soto
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|url = https://e-archivo.uc3m.es/bitstream/handle/10016/2954/COMPNW_3675_08.pdf?sequence=2&isAllowed=y
}}</ref> emphasizes in the terms of efficiency in network usage and path length. That’s the main cause why it uses AMSTP, a simplified and self-configuring version of MSTP protocol.<br />
Abridges can be described as a two-tiered hierarchy of layer-two switches in which network islands running independent rapid spanning tree protocols communicate through a core formed by island root bridges (ABridges). As it has been mentioned, it is focused in terms of efficiency, this is due to the ability of AMSTP to provide optimum paths in the core mesh and the usage of [[
==== Architecture ====
[[File:Architecture ABridges.png|thumb|Two-layer network proposal for ABridges.]]
With the objective of enhancing the properties of Abridges protocol, a two-level hierarchical [[
==== Protocol Operation ====
Inside every island or access network a bridge is automatically elected to behave as the Root Bridge, this one bridge will behave as a gateway, allowing the forwarding of frames from the core to an island and conversely. Just one Abridge is going to perform these gateway functions, although many could be connected. Communication among [[IEEE 802.1D|802.1D]] bridges and between standard [[IEEE 802.1D|802.1D]] bridges and ABridges does not require point-to-point connections.<br />
The ABridge receiving an [[Address Resolution Protocol|ARP]] frame from an island host obtains the island in which the destination is located by asking an [[Address Resolution Protocol|ARP]] server where the host was previously registered by its island ABridge. This server stores the IP to [[MAC address|MAC]] mapping and the island ABridge ID. The [[Address Resolution Protocol|ARP]] servers distribute its load based on equal result of short hashing of the IP addresses served. The core self-configures and the operation is transparent to all hosts and standard switches at islands.
==== ABridges functionality ====
ABridges is composed by three basic functional modules, which could be resumed in:
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* '''AMSTP Routing:''' Routes frames between Abridges and the Gateway. It has core ports, either of them interconnect ABridges, which learn root bridge IDs from the AMSTP [[Bridge Protocol Data Unit|BPDUs]] received and store this information in a database, known as “Forwarding Database”.
* '''GateWay:''' Interconnects the above-mentioned modules.
Abridges will configure each of their [[Port (computer networking)|Ports]] to be part either of the core or of an island, this port self-configuration is done with very simple stipulations: if a port is not connected to another Abridge using a point-to-point link, it will turn itself an access port; on the other hand, [[Port (computer networking)|Ports]] directly connected to another Abridge are configured as core ports. This auto-configuration mechanism is pretty like the one used in [[
==== ARP and ABridge Resolution ====
As any layer-two based protocol, ABridges uses [[Address Resolution Protocol|ARP]] broadcasts to obtain the [[
==See also==
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{{reflist}}
== External
{{commons category|MSTP}}
* [http://standards.ieee.org/about/get/802/802.1.html IEEE "Home Page" for 802.1] (Related Standards of the 802.1 family)
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