NOTE: A port configured as an edge port, on a PVST switch, immediately transitions to the
forwarding state. Only ports connected to end-hosts should be configured as an edge port.
Consider an edge port similar to a port with a spanning-tree portfast enabled.
If you do not enable shutdown-on-violation, BPDUs are still sent to the route process
module (RPM) CPU.
You cannot enable root guard and loop guard at the same time on a port. For example,
if you configure
loop guard on a port on which root guard is already configured, 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 traffic from flowing through it. For example, when
Portfast BPDU guard and loop guard are both configured:
• If a BPDU is received from a remote device, BPDU guard places the port in an Err-
Disabled Blocking state and no traffic 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 traffic is forwarded on the port.
Example
FTOS(conf-if-gi-1/1)#spanning-tree pvst vlan 3 cost 18000
FTOS(conf-if-gi-1/1)#end
FTOS(conf-if-gi-1/1)#show config
!
interface GigabitEthernet 1/1
no ip address
switchport
spanning-tree pvst vlan 3 cost 18000
no shutdown
FTOS(conf-if-gi-1/1)#end
FTOS#
Related
Commands
show spanning-tree pvst – views the PVST+ configuration.
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.
C-Series, E-Series, S-Series, Z-Series, S4810
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
1175
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