Allied Telesis AlliedWare Plus Operating System Version 5.4.4C (x310-26FT,x310-26FP,x310-50FT,x310-50FP) - Manual (Page 479)

Spanning Tree Introduction: STP, RSTP, and MSTP
Software Reference for x310 Series Switches
C613-50046-01 REV A AlliedWare Plus TM Operating System - Version 5.4.4C 18.11
Multiple Spanning Tree Protocol (MSTP)
Conceptually, MSTP views the total bridged network as one that comprises a number of
Multiple Spanning Tree Regions (MSTRs), where each region can contain up to 64 spanning
trees, which operate locally, called Multiple Spanning Tree Instances (MSTIs).
AlliedWare Plus
TM
supports up to 15 MSTIs. The regions are linked by the Common Internal
Spanning Tree (CIST).
MSTP uses BPDUs to exchange information between spanning-tree compatible devices, to
prevent loops in each MSTI and also in the CIST, by selecting active and blocked paths.
This process is described in
Table 18-1 .
If multiple ports are aggregated together into a dynamic (LACP) or static channel group,
then the spanning-tree process is aware of the link aggregation and treats the aggregated
ports as a single logical path.
Advantage of
MSTP over RSTP
MSTP is similar to RSTP, in that it provides loop resolution and rapid convergence.
However, RSTP can keep track of only one spanning-tree. MSTP can track many spanning-
trees, referred to as instances. MSTP makes it possible to have different forwarding paths
for different MST instances. This enables load balancing of network traffic across
redundant links, so that all the links in a network can be used by at least one MSTI, and no
link is left completely idle. That is to say that no link is unnecessarily shut down by
spanning-tree.
Essentially, MSTP is VLAN aware and RSTP is not VLAN aware. MSTP BPDUs and RSTP
BPDUs are compatible, so a network can have a mixture of MSTP and RSTP areas.