Information Technology Reference
In-Depth Information
Table 20-3 outlines the problems that might cause this symptom and describes solutions to those
problems.
Table20-3 Transparent Bridging: Unstable Spanning Tree
Possible Causes
Suggested Actions
Link flapping
1.
Use
show span
command to check whether the number of
topology changes is steadily increasing.
2.
If so, check the link between your bridges, using the
show
interface
command. If you cannot find a link flapping
between two bridges this way, use the
debug spantree event
privileged exec command on your bridges.
This will log all changes related to Spanning Tree; in a stable
topology, there should not be any. The only links to track are the
ones connecting bridging devices—a transition on a link to an end
station should have no impact on the network.
Caution
: Exercise caution when using the
debug spantree event
command. Because debugging output is assigned high priority in
the CPU process, it can render the system unusable. For this
reason, use
debug
commands only to troubleshoot specific
problems or during troubleshooting sessions with Cisco technical
support staff. Moreover, it is best to use
debug
commands during
periods of lower network traffic and fewer users. Debugging
during these periods decreases the likelihood that increased
debug
command processing overhead will affect system use.
