Configuring Multiple Spanning Trees
MSTP generates a unique spanning tree for each in stance. Th is provides multiple
pathways across the network, thereby balancing the traffic load, preventi ng
wide-scale disruption when a bridge node in a single instance fails, and allow ing 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 supp orts up
to 33 instances. You should try to group VLANs which cover the same general a rea
of your network. However, remember that you must configure all bridges within the
same MSTI Region (page 10-8) with the sam e 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 Comm on Sp ann ing
Tree.
To use multiple spanning trees:
1. Set the spanning tree type to MSTP (STA Configuration, page 10-6).
2. Enter the spanning tree priority for the selected MST instance (MSTP VLAN
Configuration).
3. Add the VLANs that will share this MSTI (MSTP VLAN Conf igurat ion).
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.
Command Attributes
• MST Instance – Instance identifier of this spanning tree. ( Default: 0)
• Priority – The priority of a s panning tree ins tance. (Range: 0- 61440 in s teps of
4096; Options: 0, 4096, 8192, 12288, 16384, 20480, 24576, 28672, 32768, 36864,
40960, 45056, 49152, 53248, 57344, 61440; Default: 32768)
• VLANs in MST Instance – VLANs assigned thi s instance.
• MST ID – Instance identifier to configure. (R ange: 0-409 4; Defaul t: 0)
• VLAN ID – VLAN to assign to this selec ted MST ins tance . (Range: 1- 4093)
The other global attributes are described under “Displaying Global Settings,” page 10-3. The
attributes displayed by the CLI for individual interfaces are described under “Displaying Interface
Settings,” page 10-10

10-16

Spanning Tree Algorithm

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