You will get a lot more replies from users if you open new incidents for new problems/alerts
the alert you seen there can be caused by unidirectional link detection , can be caused by a cable failure or by no bpdus were seen coming into the interface but it looks to have tresolved itself
you can check if there is still an issue with command show spanning-tree inconsistentports
http://www.cisco.com/c/en/us/support/docs/lan-switching/spanning-tree-protocol/10596-84.html#loop_guard
Cisco
STP Loop Guard
Feature Description
The STP loop guard feature provides additional protection against Layer 2 forwarding loops (STP loops). An STP loop is created when an STP blocking port in a redundant topology erroneously transitions to the forwarding state. This usually happens because one of the ports of a physically redundant topology (not necessarily the STP blocking port) no longer receives STP BPDUs. In its operation, STP relies on continuous reception or transmission of BPDUs based on the port role. The designated port transmits BPDUs, and the non-designated port receives BPDUs.
When one of the ports in a physically redundant topology no longer receives BPDUs, the STP conceives that the topology is loop free. Eventually, the blocking port from the alternate or backup port becomes designated and moves to a forwarding state. This situation creates a loop.
The loop guard feature makes additional checks. If BPDUs are not received on a non-designated port, and loop guard is enabled, that port is moved into the STP loop-inconsistent blocking state, instead of the listening / learning / forwarding state. Without the loop guard feature, the port assumes the designated port role. The port moves to the STP forwarding state and creates a loop.
When the loop guard blocks an inconsistent port, this message is logged:
-
CatOS
%SPANTREE-2-LOOPGUARDBLOCK: No BPDUs were received on port 3/2 in vlan 3. Moved to
loop-inconsistent state.
-
Cisco IOS
%SPANTREE-2-LOOPGUARD_BLOCK: Loop guard blocking port FastEthernet0/24 on
VLAN0050.
Once the BPDU is received on a port in a loop-inconsistent STP state, the port transitions into another STP state. According to the received BPDU, this means that the recovery is automatic and intervention is not necessary. After recovery, this message is logged:
-
CatOS
%SPANTREE-2-LOOPGUARDUNBLOCK: port 3/2 restored in vlan 3.
-
Cisco IOS
%SPANTREE-2-LOOPGUARD_UNBLOCK: Loop guard unblocking port FastEthernet0/24 on
VLAN0050.
