Allied Telesis AT-8100 Series - Manual (Page 860)

Chapter 58: Multiple Spanning Tree Protocol (MSTP)
860
MSTI Guidelines
Following are several guidelines to keep in mind about MSTIs:
 The AT-8100 Switch can support up to 15 spanning tree instances,
including the Common and Internal Spanning Tree (CIST).
 An MSTI can contain any number of VLANs.
 A VLAN can belong to only one MSTI at a time.
 A switch port can belong to more than one spanning tree instance
at a time by being an untagged and tagged member of VLANs
belonging to different MSTIs. This is possible because a port can
be in different MSTP states for different MSTIs simultaneously. For
example, a port can be in the MSTP blocking state for one MSTI
and the forwarding state for another spanning tree instance. For
further information, refer to “Ports in Multiple MSTIs” on page 862.
 A router or Layer 3 network device is required to forward traffic
between different VLANs.