Information Technology Reference
In-Depth Information
Table20-3 Transparent Bridging: Unstable Spanning Tree (continued)
Possible Causes
Suggested Actions
Root bridge that
keeps
changing/multipl
e bridges that
claim to be the
root
Check the consistency of the root bridge information all over
the bridged network using the
show span
commands on the
different bridges.
1.
If several bridges are claiming to be the root, check that you
are running the same Spanning-Tree Protocol on every bridge
(see the entry “Spanning-Tree Algorithm mismatch,” in Table
20-5).
2.
Use the
bridge <group> priority <number>
command on
root bridge to force the desired bridge to become the root. The
lower the priority, the more likely the bridge is to become the
root.
3.
Check the diameter of your network. With standard Spanning
Tree settings, there should never be more that seven bridging
hops between two hosts.
4.
Hellos not being
exchanged
1.
Check whether bridges are communicating with one another.
Use a network analyzer or the
debug spantree tree
privileged
exec command to see whether Spanning Tree hello frames are
being exchanged.
Caution
: Exercise caution when using the
debug spantree tree
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.
2.
If hellos are not being exchanged, check the physical
connections and software configuration on bridges.
Transparent Bridging: Sessions Terminate Unexpectedly
Symptom
: Connections in a transparently bridged environment are successfully established, but
sessions sometimes terminate abruptly.
