Allied Telesis AT-S63 - Manual (Page 283)

AT-S63 Management Software Menus Interface User’s Guide
Section II: Advanced Features 283
❑ An AT-9400 Series switch 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 port on the switch can belong to only one spanning tree
instance at a time. This means that a port cannot be a tagged and
untagged member of VLANs that belong to different MSTIs. For
example, if port 1 is an untagged port on one VLAN and a tagged
port in three other VLANs, all four VLANs must be assigned to the
same MSTI. This rule is required because a port can be either
blocking or forwarding. Aport cannot perform both functions
sumultaneously, which could occur if it was a member of VLANs
that resided in different spanning tree instances.
❑ 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 number
❑ 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.
The revision number is an arbitrary number you assign to a region. This
number can be used to keep track of the revision level of a region’s
configuration. For example, you might use this value to maintain the
number of times you revise a particular MSTP region. It is not important