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2. Enable STP BPDU guard in INTERFACE mode.

spanning-tree bpduguard enable

BPDU guard violation causes the system to perform the following actions in the port channel:

● The interface and all member ports are disabled in the hardware.

● When the port is added to the port channel that is in the Error Disable state, the new member port is disabled in the

hardware.

● When the port is removed from the port channel that is in the Error Disable state, the system clears the Error_Disabled

state on the physical port and enables it in the hardware.

To clear the Error Disabled state:

● Use the shutdown command on the interface.

● Use the spanning-tree bpduguard disable command to disable the BPDU guard on the interface.

● Use the spanning-tree disable command to disable STP on the interface.

3. Set the guard types to avoid loops in INTERFACE mode.

spanning-tree guard {loop | root | none}

● loop — Set the guard type to loop.

● root — Set the guard type to root.

● none — Set the guard type to none.

Port enabled with loop guard conditions

● Loop guard is supported on any STP-enabled port or port-channel interface.

● You cannot enable root guard and loop guard at the same time on an STP port. The loop guard configuration overwrites

an existing root guard configuration and vice versa.

● Enabling BPDU guard and loop guard at the same time on a port results in a port that remains in blocking state and

prevents traffic from flowing through it. For example, when you configure both Portfast BPDU guard and loop guard:

○ If a BPDU is received from a remote device, BPDU guard places the port in the Err-Disabled Blocking state and no

traffic forwards on the port.

○ If no BPDU is received from a remote device which was sending BPDUs, loop guard places the port in the Loop-

Inconsistent Blocking state and no traffic forwards on the port.

● When used in a Rapid-PVST network, STP loop guard performs per-port or per port-channel at a VLAN level. If no

BPDUs are received on a port-channel interface, the port or port-channel transitions to a Loop-Inconsistent or Blocking

state only for this VLAN.

BPDU filter

os10(conf-if-eth1/1/7)# spanning-tree bpdufilter enable

os10(conf-if-eth1/1/7)# do show spanning-tree interface ethernet 1/1/7

ethernet1/1/7 of vlan 1 is Designated Forwarding

Edge port: No (default)

Link type: point-to-point (auto)

Boundary: No, Bpdu-filter: Enable, Bpdu-Guard: Disable, Shutdown-on-Bpdu-Guard-

violation: No

Root-Guard: Disable, Loop-Guard: Disable

Bpdus (MRecords) Sent: 6, Received: 6410

Interface Designated

Name PortID Prio Cost Sts Cost Bridge ID PortID

-----------------------------------------------------------------------------------------

ethernet1/1/7 128.56 128 500 FWD 500 32769 90b1.1cf4.a625 128.56

BPDU guard

os10(config)# interface ethernet 1/1/7

os10(conf-if-eth1/1/7)# spanning-tree bpduguard enable