Multiple Spanning Tree Protocol
The Multiple Spanning Tree Protocol (MSTP) and algorithm, provides both simple and full connectivity assigned to any given virtual LAN (VLAN) throughout a bridged local area network.
MSTP uses bridge protocol data unit (BPDUs) to exchange information between spanning-tree compatible devices, to prevent loops in each Multiple Spanning Tree instance (MSTI) and in the common and internal spanning tree (CIST), by selecting active and blocked paths.
This is done as well as in Spanning Tree Protocol (STP) without the need of manually enabling backup links and getting rid of switching loop danger.
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.
Its main function is enabling MSTP to select its root bridges for the proper CIST and each MSTI.
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 802.1D, 2004,[2] followed by components that are specific to CIST -octets 37 to 102.
MSTP is designed to be STP and RSTP compatible and interoperable without additional operational management practice, this is due to a set of measurements based on RSTP (Clause 17 of IEEE Std 802.1D, 2004 Edition) intending to provide the capability for frames assigned to different VLANs, to be transmitted along different paths within MST Regions.
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 LANs segments by devices other than the Bridges that operate invisibly with respect to support of the Bridges' MAC Internal Sublayer Service.
This section is mainly oriented to provide any user a proper manner of configuring a MSTP network over Cisco devices.
[8] AMSTP is a simplified one tree instance rooted at each edge bridge in the core to forward frames.
Every ABridge, except for the elected root bridge, creates an AM-Record for its own spanning tree instances.
The ARP servers distribute its load based on equal result of short hashing of the IP addresses served.
That is the main cause why avoiding overflooding is a matter of paramount priority; to limit this broadcast traffic, is recommended the use of distributed load ARP servers, although its use is not compulsory.
