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• 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.Example
The following example configures the switch to use Rapid Spanning Tree:
Console(config)#spanning-tree mode rstp
Console(config)#
spanning-tree forward-time
This command configures the spanning tree bridge forward time globally for this
switch. Use the no form to restore the default.
Syntax
spanning-tree forward-time seconds
no spanning-tree forward-time
seconds - Time in seconds. (Range: 4 - 30 seconds)
The minimum value is the higher of 4 or [(max-age / 2) + 1].
Default Setting
15 seconds
Command Mode
Global Configuration
Command Usage
This command sets the maximum time (in seconds) the root device will wait
before changing states (i.e., discarding to learning to forwarding). This delay is
required because every device must receive information about topology
changes before it starts to forward frames. In addition, each port needs time to
listen for conflicting information that would make it return to the discarding
state; otherwise, temporary data loops might result.
Spanning Tree Commands
4-127
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