Allied Telesis AlliedWare Plus Operating System Version 5.4.4C (x310-26FT,x310-26FP,x310-50FT,x310-50FP) - Manual (Page 480)

Spanning Tree Introduction: STP, RSTP, and MSTP
Software Reference for x310 Series Switches
18.12 AlliedWare Plus TM Operating System - Version 5.4.4C C613-50046-01 REV A
Multiple Spanning Tree Instances (MSTI)
MSTP enables the grouping and mapping of VLANs to different spanning tree instances.
So, an MST Instance (MSTI) is a particular set of VLANs that are all using the same spanning
tree.
In a network where all VLANs span all links of the network, judicious choice of bridge
priorities for different MSTIs can result in different switches becoming root bridges for
different MSTIs. That will result in the different MSTIs choosing different active topologies
on the network. An example of how different MSTIs can choose different active topologies
on the same physical set of links is illustrated in
Figure 18-1 .
MSTP is compatible with RSTP and STP—see “Common and Internal Spanning Tree
(CIST)” on page 18.15 .
Figure 18-1: Different spanning trees created by different MSTIs on the same
physical layout
Physical connections
Spanning tree of MSTI= 1 containing vlans 2, 7, 9, 43
Spanning tree of MSTI= 2 containing vlans 16, 18, 24, 40
Spanning tree of MSTI= 3 containing vlans 23, 39, 50, 112
Diff_MSTI_1
Root bridge for
MSTI 1
Root bridge for
MSTI 2
Root bridge for
MSTI 3