Dell S4048T-ON, Configuration Manual

Page: 935 / 1146

Configuring Loop Guard
Enable STP loop guard on a per-port or per-port channel basis.
The following conditions apply to a port enabled with loop guard:
• Loop guard is supported on any STP-enabled port or port-channel interface.
• Loop guard is supported on a port or port-channel in any spanning tree mode:
•
Spanning Tree Protocol (STP)
• Rapid Spanning Tree Protocol (RSTP)
• Multiple Spanning Tree Protocol (MSTP)
• Per-VLAN Spanning Tree Plus (PVST+)
• You cannot enable root guard and loop guard at the same time on an STP 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
.
• 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.
• When used in a PVST+ network, STP 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.
To enable a loop guard on an STP-enabled port or port-channel interface, use the following command.
• Enable loop guard on a port or port-channel interface.
INTERFACE mode or INTERFACE PORT-CHANNEL mode
spanning-tree {0 | mstp | rstp | pvst} loopguard
•
0
: enables loop guard on an STP-enabled port assigned to instance 0.
•
mstp
: enables loop guard on an MSTP-enabled port.
•
rstp
: enables loop guard on an RSTP-enabled port.
•
pvst
: enables loop guard on a PVST-enabled port.
To disable STP loop guard on a port or port-channel interface, use the
no spanning-tree 0 loopguard
command in an INTERFACE
configuration mode.
To verify the STP loop guard configuration on a port or port-channel interface, use the
show spanning-tree 0 guard
[interface interface ]
command in a global configuration mode.
Displaying STP Guard Configuration
To display the STP guard configuration, use the following command.
The following example shows an STP network (instance 0) in which:
• Root guard is enabled on a port that is in a root-inconsistent state.
• Loop guard is enabled on a port that is in a listening state.
• BPDU guard is enabled on a port that is shut down (Error Disabled state) after receiving a BPDU.
• Verify the STP guard configured on port or port-channel interfaces.
show spanning-tree 0 guard [interface interface ]
Spanning Tree Protocol (STP) 935