7-17
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When the root bridge of an instance fails or is shut down, the secondary root bridge (if you have
specified one) can take over the role of the primary root bridge. However, if you specify a new
primary root bridge for the instance then, the secondary root bridge will not become the root bridge.
If you have specified multiple secondary root bridges for an instance, when the root bridge fails,
MSTP will select the secondary root bridge with the lowest MAC address as the new root bridge.
Configuring the AP as the root bridge of a spanning tree
Follow these steps to configure the AP as the root bridge of a spanning tree:
To do...
Use the command...
Remarks
Enter system view
system-view
—
Configure the AP as the
root bridge of a spanning
tree
stp
[
instance instance-id
]
root
primary
Required
By default, the AP does not function as the
root bridge of any spanning tree.
Configuring the AP as a secondary root bridge of a spanning tree
Follow these steps to configure the AP as a secondary root bridge of a spanning tree:
To do...
Use the command...
Remarks
Enter system view
system-view
—
Configure the AP as a
secondary root bridge of a
spanning tree
stp
[
instance instance-id
]
root secondary
Required
By default, the AP does not function as a
secondary root bridge.
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After specifying the AP as the root bridge or a secondary root bridge, you cannot change the
priority of the AP.
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Alternatively, you can also configure the AP as the root bridge by setting the priority of the AP to 0.
For more information about AP priority configuration, see
Configuring the Priority of the AP
Configuring the MSTP Work Mode of the AP
Being mutually compatible, MSTP and RSTP can recognize each other’s protocol packets. However,
STP cannot recognize MSTP packets. For hybrid networking with legacy STP devices and for full
interoperability with RSTP-enabled devices, MSTP supports three work modes: STP-compatible mode,
RSTP mode, and MSTP mode.
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In STP-compatible mode, all ports of the device send out STP BPDUs,
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In RSTP mode, all ports of the device send out RSTP BPDUs. If the device detects that it is
connected with a legacy STP device, the port connecting with the legacy STP device will
automatically migrate to STP-compatible mode.
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In MSTP mode, all ports of the device send out MSTP BPDUs. If the device detects that it is
connected with a legacy STP device, the port connecting with the legacy STP device will
automatically migrate to STP-compatible mode.
Make this configuration on the root bridge and on the leaf nodes separately.
