Allied Telesis AT-S60 - Manual (Page 269)

AT-S60 Management Software User’s Guide
Section II: Advanced Features 269
❑ 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’s associated with
another MSTI ID. However, in determining network loops, MSTI
takes precedence over CIST. (This is explained in more detail in
Associating VLANs to MSTIs on page 269.)
Note
Due to different vendor implementations of the new IEEE 802.1s
standard, compatibility issues concerning MSTP instances between
the AT-8400 Series switch and switches from other vendors may
exist. This can result in compatibility issues between different MSTP
implementations. For this release, MSTP is compatible only with
other AT-8400 Series switches.
Associating VLANs to MSTIs
Allied Telesyn recommends that you assign all VLANs on a switch to an
MSTI. You should not leave a VLAN assigned to just the CIST, including
the Default_VLAN. This is to prevent the blocking of a port that should
be in the forwarding state. The reason for this guideline is explained
below.
An MSTP BPDU contains the instance to which the port transmitting the
packet belongs. By default, all ports belong to the CIST instance. So CIST
would be included in the BPDU. If the port is a member of a VLAN that
has been assigned to another MSTI, that information is also included in
the BPDU.