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Model name
Multiple Spanning Tree
The Switch allows the above Spanning Tree Protocols to be used as standalone or together.
The following table describes which Spanning Tree combinations can be applied.
Table 19-2 Spanning Tree combinations and applicability
Tree building condition
Standalone PVST+
Standalone Single Spanning Tree
Combination of PVST+ and Single
Spanning Tree
Standalone Multiple Spanning Tree
Note: Multiple Spanning Tree cannot be used in combination with other trees.
19.1.3 Spanning Tree Protocols and rapid Spanning Tree Protocols
There are two types of PVST+ and Single Spanning Tree: IEEE 802.1D Spanning Tree
Protocols and IEEE 802.1w rapid Spanning Tree Protocols. These are called PVST+ and
Rapid PVST+, and STP and Rapid STP.
When a communication path changes, the topology calculation for the Spanning Tree
Protocol immediately puts the port in Blocking status (communication is not possible),
switches to multiple statuses, and then puts it in Forwarding status (communication is
possible). Because IEEE 802.1D Spanning Tree Protocols perform this status transition by
a timer, a set time is required until communication is possible. IEEE 802.1w rapid Spanning
Tree Protocols omit this timer-based waiting time for status transitions to perform
high-speed status transitions, minimizing the time for which communication is stopped due
to topology changes.
Note that because Multiple Spanning Tree is standardized under IEEE 802.1s, the status
transition times is the same as for IEEE 802.1w. The following table describes the status
transitions for each protocol, and their corresponding required times.
Table 19-3 Status transitions for PVST+ and STP (Single Spanning Tree)
Status
Disable
Build unit
Per-MST-instance
Status overview
Status in which a port cannot be used. This transitions to
Blocking as soon as the port becomes available.
Overview
This kind of Spanning Tree Protocol is built by
groups of multiple VLANs, called MST instances. If
multiple VLANs belong to a single port, different tree
build results are applied to each MST instance.
Applicable topology calculation results
A Spanning Tree Protocol for each VLAN is applied to
VLANs for which PVST+ is running. The Spanning Tree
Protocol is not applied to other VLANs.
PVST+ runs by default on port VLANs for the Switch.
Single Spanning Tree is applied to all VLANs.
All PVST+ instances are stopped in this configuration.
A Spanning Tree Protocol for each VLAN is applied to
VLANs for which PVST+ is running. Single Spanning Tree is
applied to other VLANs.
Multiple Spanning Tree is applied to all VLANs.
19 Spanning Tree Protocol
Transition to the next
status
n/a
297
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