Allied Telesis AT-S62 - Manual (Page 358)

Chapter 19: Multiple Spanning Tree Protocol
Section IV: Spanning Tree Protocols 358
MSTI Guidelines
Here are several guidelines to keep in mind about MSTIs:
❑ An AT-8524M can support up to 16 spanning tree instances,
including the CIST, at a time.
❑ A 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. This allows you to assign a port as a tagged and
untagged member of VLANs that belong to different MSTIs. What
makes this possible is a port’s ability to be in different MSTP states
for different MSTIs. For example, a port can be in the MSTP
blocking state for one MSTI and the forwarding state for another
spanning tree instance, simultaneously.
❑ A router or Layer 3 network device is required to forward traffic
between different VLANs.
VLAN and MSTI
Associations
Part of the task to configuring MSTP involves assigning VLANs to
spanning tree instances. The mapping of VLANs to MSTIs is called
associations. A VLAN, either port-based or tagged, can belong to only
one instance at a time, but an instance can contain any number of
VLANs.
Multiple
Spanning Tree
Regions
Another important concept of MSTP is regions. A MSTP region is defined
as a group of bridges that share exactly the same MSTI characteristics.
Those characteristics are:
❑ Configuration name
❑ Revision level
❑ VLANs
❑ VLAN to MSTI ID associations
A configuration name is a name you assign to a region to help you
identify it. You must assign each bridge in a region exactly the same
name; even the same upper and lowercase lettering. Identifying the
regions in your network is easier if you choose names that are
characteristic of the functions of the nodes and bridges of the region.
Examples are Sales Region and Engineering Region.