Summary of guidelines – Allied Telesis AT-S63 User Manual
Page 303
AT-S63 Management Software Features Guide
Section V: Spanning Tree Protocols
303
Summary of Guidelines
Careful planning is essential for the successful implementation of MSTP.
This section reviews all the rules and guidelines mentioned in earlier
sections, and contains a few new ones:
The AT-9400 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.
An MSTI ID can be from 1 to 15.
The CIST ID is 0. You cannot change this value.
A switch port can belong to more than one spanning tree instance at a
time. This allows you to assign a port as an untagged and tagged
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 simultaneously. For example, a port can be in the MSTP
blocking state for one MSTI and the forwarding state for another
spanning tree instance.
A router or Layer 3 network device is required to forward traffic
between VLANs.
A network can contain any number of regions and a region can contain
any number of AT-9400 Switches.
The AT-9400 Switch can belong to only one region at a time.
A region can contain any number of VLANs.
All of the bridges in a region must have the same configuration name,
revision level, VLANs, and VLAN to MSTI associations.
An MSTI cannot span multiple regions.
Each MSTI must have a regional root for locating loops in the instance.
MSTIs can share the same regional root or have different roots. A
regional root is determined by the MSTI priority value and a bridge’s
MAC address.
The regional root of a MSTI must be in the same region as the MSTI.
The CIST must have a regional root for communicating with other
regions and single-instance spanning trees.
MSTP is compatible with STP and RSTP.
A port transmits CIST information even when it is associated with
another MSTI ID. However, in determining network loops, MSTI takes
precedence over CIST. (This is explained more in “Associating VLANs
to MSTIs” on page 305.