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Catalyst 4500 Series, Catalyst 2948G, Catalyst 2948G-GE-TX, and Catalyst 2980G Switches Software Configuration Guide—Release 8.2GLX
78-15908-01
Chapter 7 Configuring Spanning Tree
Using Rapid PVST+
Disabling the PVST+ Mode on a VLAN
When the switch is in PVST+ mode, you can disable spanning tree on individual VLANs or all VLANs.
When you disable spanning tree on a VLAN, the switch does not participate in spanning tree and any
BPDUs that are received in that VLAN are flooded on all ports.
Caution
Do not disable spanning tree on a VLAN unless all switches and bridges in the VLAN have spanning
tree disabled. You cannot disable spanning tree on some switches or bridges in a VLAN and leave it
enabled on other switches or bridges in the VLAN. Doing so can have unexpected results because
switches and bridges with spanning tree enabled will have incomplete information regarding the physical
topology of the network.
Caution
We do not recommend disabling spanning tree, even in a topology that is free of physical loops. Spanning
tree serves as a safeguard against misconfigurations and cabling errors. Do not disable spanning tree in
a VLAN without ensuring that there are no physical loops present in the VLAN.
To disable PVST+ mode, perform this task in privileged mode:
This example shows how to disable PVST+ on a VLAN:
Console> (enable) set spantree disable 4
Spantree 4 disabled.
Console> (enable)
Using Rapid PVST+
To configure Rapid PVST+, you need to also configure PVST+ on your switch. You can configure
PVST+ either before or after you enable Rapid PVST+.
To configure Rapid PVST+, perform this task in privileged mode:
Task
Command
Disable PVST+ mode on a VLAN.
set spantree disable vlans [all]
Task
Command
Step 1
Enable Rapid PVST+.
set spantree mode rapid-pvst+
Step 2
Set the link type to point-to-point mode for
the port.
set spantree link-type mod/port point-to-point
Step 3
If any port on the switch is connected to a
port on a PVST+ switch, check for any
legacy bridges on the port.
clear spantree detected-protocols mod/port
Step 4
Verify the Rapid PVST+ configuration.
show spantree vlan