| Spanning Tree Commands
Spanning Tree Protocol
This option uses RSTP set to STP forced compatibility mode. It uses RSTP for the
internal state machine, but sends only 802.1D BPDUs. This creates one
spanning tree instance for the entire network. If multiple VLANs are
implemented on a network, the path between specific VLAN members may be
inadvertently disabled to prevent network loops, thus isolating group
members. When operating multiple VLANs, we recommend selecting the MSTP
Rapid Spanning Tree Protocol
RSTP supports connections to either STP or RSTP nodes by monitoring the
incoming protocol messages and dynamically adjusting the type of protocol
messages the RSTP node transmits, as described below:
STP Mode – If the switch receives an 802.1D BPDU after a port's migration
delay timer expires, the switch assumes it is connected to an 802.1D bridge
and starts using only 802.1D BPDUs.
RSTP Mode – If RSTP is using 802.1D BPDUs on a port and receives an RSTP
BPDU after the migration delay expires, RSTP restarts the migration delay
timer and begins using RSTP BPDUs on that port.
Multiple Spanning Tree Protocol
To allow multiple spanning trees to operate over the network, you must
configure a related set of bridges with the same MSTP configuration,
allowing them to participate in a specific set of spanning tree instances.
A spanning tree instance can exist only on bridges that have compatible
VLAN instance assignments.
Be careful when switching between spanning tree modes. Changing
modes stops all spanning-tree instances for the previous mode and restarts
the system in the new mode, temporarily disrupting user traffic.
The following example configures the switch to use Rapid Spanning Tree:
Console(config)#spanning-tree mode rstp
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