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Chapter 2
Messages and Recovery Procedures
from the designated bridge. This feature is mainly used to detect unidirectional links. The first
[chars] is the loopguard state (enable or disable), the second [chars] is the interface name, and the
third [chars] is the spanning-tree instance.
Recommended Action
this is not the desired configuration; otherwise, no further action is required.
Error Message SPANTREE-2-LOOPGUARD_UNBLOCK: Loop guard unblocking port [chars] on
[chars].
Explanation
inconsistency was caused by a unidirectional link failure, the problem no longer exists. The
loopguard-inconsistency is cleared for the interface, which is taken out of the blocking state, if
appropriate. The first [chars] is the port name, and the second [chars] is the spanning-tree mode
displayed in the show spanning-tree privileged EXEC command.
Recommended Action
Error Message SPANTREE-2-PVSTSIM_FAIL: Superior PVST BPDU received on VLAN [dec]
port [chars], claiming root [dec]:[enet]. Invoking root guard to block the port.
Explanation
loop. When a PVST+ switch is connected to an MST switch, the IST root (MSTOO) becomes the
root for all PVST+ spanning trees. A loop can occur if any of the PVST+ spanning trees have a better
root than IST. To prevent the loop, root guard blocks the port on the MST switch that receives the
superior message from the PVST+ side. The first [dec] is the VLAN ID, [chars] is the short interface
name, such as Gi0/1, the second [dec] is the root bridge priority, and [enet] is the root bridge MAC
address.
Recommended Action
topology, root guard might temporarily block the port and then automatically restore it. If the port
remains blocked, identify the root bridge from this error message, and configure a less favorable
priority for the VLAN spanning tree. There could be other superior PVST roots, and the port cannot
recover until all such roots are cleared. Alternatively, try disabling and then enabling the VLAN
port.
Error Message SPANTREE-2-RECV_1Q_NON_1QTRUNK: Received 802.1Q BPDU on non 802.1Q
trunk [chars] [chars].
Explanation
(SSTP) BPDU was received was in trunk mode but was not using 802.1Q encapsulation. The first
[chars] is the port, and the second [chars] is the VLAN.
Recommended Action
that of the interface to which it is connected are in the same mode (access or trunk). If the mode is
trunk, verify that both interfaces have the same encapsulation (none or 802.1Q). When the
encapsulation is consistent, spanning tree automatically unblocks the interface.
OL-9641-01
Verify that this is the desired configuration for the listed interface. Correct it if
This message means that the listed interface has received a BPDU, and therefore, if the
No action is required.
This message means that root guard blocked a port that might cause a spanning-tree
When spanning tree converges after a new switch or switch port is added to the
This message means that the listed interface on which a Shared Spanning Tree Protocol
Verify that the configuration and operational state of the listed interface and
Cisco ME 3400 and 2400 Ethernet Access Switch System Message Guide
SPANTREE Messages
2-61
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