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Cisco ME 3400E, ME 3400, and ME 2400 Ethernet Access Switch System Message Guide
OL-9641-04
Chapter 2 Messages and Recovery Procedures
SPANTREE Messages
loopguard-inconsistent to prevent possible loops from being created. 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
Enter the
show spanning-tree inconsistentports
privileged EXEC command
to review the list of interfaces with loopguard inconsistencies. Find out why devices connected to
the listed ports are not sending BPDUs. One reason might be that they are not running the STP. If
so, you should disable loop guard on the inconsistent interfaces by using the
spanning-tree guard
none
interface configuration command or by starting the STP on the remote side of the links.
Error Message
SPANTREE-2-LOOPGUARD_CONFIG_CHANGE: Loop guard [chars] on port [chars]
on [chars].
Explanation
This message means that the spanning-tree loopguard configuration for the listed
interface has been changed. If enabled, the interface is placed into the blocking state. It is marked
as loopguard-inconsistent when the message-age timer expires because no BPDUs were received
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
Verify that this is the desired configuration for the listed interface. Correct it if
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
This message means that the listed interface has received a BPDU, and therefore, if the
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
No action is required.
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
This message means that root guard blocked a port that might cause a spanning-tree
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
When spanning tree converges after a new switch or switch port is added to the
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.