Chapter 17
| Spanning Tree Commands
– 415 –
spanning-tree mode
This command selects the spanning tree mode for this switch. Use the
no
form to restore the default.
Syntax
spanning-tree mode
{
stp
|
rstp
|
mstp
}
no spanning-tree mode
stp
- Spanning Tree Protocol (IEEE 802.1D)
rstp
- Rapid Spanning Tree Protocol (IEEE 802.1w)
mstp
- Multiple Spanning Tree (IEEE 802.1s)
Default Setting
rstp
Command Mode
Global Configuration
Command Usage
◆
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 option.
◆
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.
