Chapter 7
| Spanning Tree Algorithm
Configuring Multiple Spanning Trees
– 224 –
Configuring Multiple Spanning Trees
Use the Spanning Tree > MSTP (Configure Global) page to create an MSTP instance,
or to add VLAN groups to an MSTP instance.
Command Usage
MSTP generates a unique spanning tree for each instance. This provides multiple
pathways across the network, thereby balancing the traffic load, preventing wide-
scale disruption when a bridge node in a single instance fails, and allowing for
faster convergence of a new topology for the failed instance.
By default all VLANs are assigned to the Internal Spanning Tree (MST Instance 0)
that connects all bridges and LANs within the MST region. This switch supports up
to 33 instances. You should try to group VLANs which cover the same general area
of your network. However, remember that you must configure all bridges within
the same MSTI Region (page 211) with the same set of instances, and the same
instance (on each bridge) with the same set of VLANs. Also, note that RSTP treats
each MSTI region as a single node, connecting all regions to the Common Spanning
Tree.
To use multiple spanning trees:
1. Set the spanning tree type to MSTP (page 211).
2. Enter the spanning tree priority for the selected MST instance on the Spanning
Tree > MSTP (Configure Global - Add) page.
3. Add the VLANs that will share this MSTI on the Spanning Tree > MSTP
(Configure Global - Add Member) page.
Note:
All VLANs are automatically added to the IST (Instance 0).
To ensure that the MSTI maintains connectivity across the network, you must
configure a related set of bridges with the same MSTI settings.
Parameters
These parameters are displayed:
◆ MST ID – Instance identifier to configure. (Range: 0-4094)
◆ VLAN ID – VLAN to assign to this MST instance. (Range: 1-4094)
◆ Priority – The priority of a spanning tree instance. (Range: 0-61440 in steps of
4096; Options: 0, 4096, 8192, 12288, 16384, 20480, 24576, 28672, 32768, 36864,
40960, 45056, 49152, 53248, 57344, 61440; Default: 32768)
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