Troubleshooting guide

3. Troubleshooting Functional Failures During Operation
35
Table 3-16 Failure analysis method for Spanning Tree
No. Items to check and commands Action
1 Execute the show
spanning-tree operation
command for Spanning Tree that
caused the failure, and then check
the status of the protocol for
Spanning Tree.
If the displayed status is Enable, go to No. 2.
If the displayed status is Disable, Spanning Tree has stopped.
Check the following configurations:
 spanning-tree disable
 switchport backup
2 Execute the show
spanning-tree operation
command for Spanning Tree that
caused the failure, and then check
the bridge identifier of the route
bridge for Spanning Tree.
If the bridge identifier of the route bridge indicates the route bridge
defined in the network configuration, go to No. 3.
If the bridge identifier of the route bridge does not indicate the
route bridge defined in the network configuration, check the
network configuration and other configurations.
3 Execute the show
spanning-tree operation
command for Spanning Tree that
caused the failure, and then check
the port status and port role for
Spanning Tree.
If the port status and port role for Spanning Tree are the same as
those defined in the network configuration, go to No. 4.
If the status of a port for which the loop guard functionality is
enabled is Blocking or Discarding, check whether the port is
a designated port.
If it is a designated port, delete the setting of the loop guard
functionality.
If the port status and port role for Spanning Tree are different from
the network configuration, check the status of neighboring devices
and their configurations.
4 Execute the show
spanning-tree statistics
operation command for Spanning
Tree that caused the failure, and
then check whether BPDUs were
sent and received on the failed port.
Check the BPDU sending or receiving counter.
For a root port:
If the BPDU receiving counter has been incremented, go to
No. 5. If the counter has not been incremented, BPDUs
might have been discarded by either filtering or the shaper of
QoS control. See
3.13.1 Checking the filtering and QoS
control configuration information and check for a problem. If
you do not find any problems, check the neighboring
devices.
For a designated port:
If the BPDU sending counter has been incremented, go to
No. 5. If the counter has not been incremented, see
3.4
Network interface communication failures.
5 Execute the show
spanning-tree detail
operation command for Spanning
Tree that caused the failure, and
then check the bridge identifier for
the received BPDUs.
Make sure the route bridge identifier and sending bridge identifier
for the received BPDUs are the same as those defined in the
network configuration. If they are different from the network
configuration, check the status of the neighboring devices.
6 Check whether the value for
maximum number of the Spanning
Tree protocols, one of which caused
the failure, is within the device
capacities.
Set a value within the device capacities.
For details about device capacities, see the Configuration Guides.