Administrator Guide

You cannot enable root guard and loop guard at the same time on a port. For example, if you congure
loop guard on a port on which root guard is already congured, the following error message is displayed: %
Error: RootGuard is configured. Cannot configure LoopGuard
.
When used in a PVST+ network, loop guard is performed per-port or per-port channel at a VLAN level. If no
BPDUs are received on a VLAN interface, the port or port-channel transitions to a Loop-Inconsistent (blocking)
state only for this VLAN.
Enabling Portfast BPDU guard and loop guard at the same time on a port results in a port that remains in a
Blocking state and prevents trac from owing through it. For example, when Portfast BPDU guard and loop
guard are both congured:
• If a BPDU is received from a remote device, BPDU guard places the port in an Err-Disabled Blocking state and
no trac is forwarded on the port.
• If no BPDU is received from a remote device, loop guard places the port in a Loop-Inconsistent Blocking state
and no trac is forwarded on the port.
Example
Dell(conf-if-gi-1/1)# spanning-tree pvst vlan 3 cost 18000
Dell(conf-if-gi-1/1)# end
Dell(conf-if-gi-1/1)# show config
!
interface GigabitEthernet 1/1
no ip address
switchport
spanning-tree pvst vlan 3 cost 18000
no shutdown
Dell(conf-if-gi-1/1)#end
Dell#
Related Commands
• show spanning-tree pvst — views the PVST+ conguration.
spanning-tree pvst err-disable
Place ports in an Err-Disabled state if they receive a PVST+ BPDU when they are members an untagged VLAN.
S3048
Syntax
spanning-tree pvst err-disable cause invalid-pvst-bpdu
Defaults Enabled; ports are placed in the Err-Disabled state if they receive a PVST+ BPDU when they are members of an
untagged VLAN.
Command Modes INTERFACE
Command History
This guide is platform-specic. For command information about other platforms, see the relevant Dell Networking
OS Command Line Reference Guide.
Version Description
9.8(1.0) Introduced on the Z9100-ON.
9.8(0.0P5) Introduced on the S4048-ON.
9.8(0.0P2) Introduced on the S3048-ON.
1250 Per-VLAN Spanning Tree Plus (PVST+)