HP procurve 8100fl series Management And Configuration Manual page 125

Region "X"
Blocks redundant
link for MSTI "B".
Switch 2
MSTI "A" Root
VLAN Memberships:
•IST Instance: VLANs 1, 2
•MSTI "A": 4, 5
•MSTI "B": 7, 9
Figure 9-3. Active Topologies Built by Three Independent MST Instances
While allowing only one active path through a given instance, MSTP retains
any redundant physical paths in the instance to serve as backups (blocked)
paths in case the existing active path fails. Thus, if an active path in an instance
fails, MSTP automatically activates (unblocks) an available backup to serve
as the new active path through the instance for as long as the original active
path is down. Note also that a given port may simultaneously operate in
different states (forwarding or blocking) for different spanning-tree instances
within the same region. This depends on the VLAN memberships to which the
port is assigned. For example, if a port belongs to VLAN 1 in the IST instance
of a region and also belongs to VLAN 4 in MSTI "x" in the same region, the port
may apply different states to traffic for these two different instances.
Within a region, traffic routed between VLANs in separate instances can take
only one physical path. To ensure that traffic in all VLANs within a region can
travel between regions, all of the boundary ports for each region should belong
to all VLANs configured in the region. Otherwise, traffic from some areas
within a region could be blocked from moving to other regions.
802.1s Multiple Spanning Tree Protocol (MSTP)
Path through IST Instance
to Other Regions
Switch 1
IST Root
VLAN Memberships:
•IST Instance: VLANs 1, 2
•MSTI "A": 4, 5
•MSTI "B": 7, 9
Blocks redundant
link for IST instance.
Spanning-Tree Operation
Blocks redundant
link for MSTI "A".
Switch 3
MSTI "B" Root
VLAN Memberships:
•IST Instance: VLANs 1, 2
•MSTI "A": 4, 5
•MSTI "B": 7, 9
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