System information

Troubleshooting Transparent Bridging
Book Title
20-426
Possible Causes Suggested Actions
Hardware or media problem
Step 1 Use the show bridge exec command to see whether there is a
connectivity problem. If there is, the output will not show any MAC
1
addresses in the bridging table.
Step 2 Use the show interfaces exec command to determine whether the
interface and line protocol are up.
Step 3 If the interface is down, troubleshoot the hardware or the media.
Refer to Chapter 3, “Troubleshooting Hardware and Booting
Problems.”
Step 4 If the line protocol is down, check the physical connection between
the interface and the network. Make sure that the connection is
secure and that cables are not damaged.
If the line protocol is up but input and output packet counters are not
incrementing, check the media and host connectivity. Refer to the
media troubleshooting chapter that covers the media type used in
your network.
Hellos not being exchanged
Step 1 Check whether bridges are communicating with one another. Use a
network analyzer or the debug spanning-tree privileged exec
command to see whether spanning-tree hello frames are being
exchanged.
Caution: Exercise caution when using the debug spanning-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.
Step 2 If hellos are not being exchanged, check the physical connections
and software configuration on bridges.
Misconfigured bridging filters Step 1 Use the show running-config privileged exec command to
determine whether bridge filters are configured.
Step 2 Disable bridge filters on suspect interfaces and determine whether
connectivity returns.
Step 3 If connectivity does not return, the filter is not the problem. If
connectivity is restored after removing filters, one or more bad filters
are causing the connectivity problem.
Step 4 If multiple filters or filters using access lists with multiple statements
exist, apply each filter individually to identify the problem filter.
Check the configuration for input and output LSAP
2
and TYPE
filters, which can be used simultaneously to block different
protocols. For example, LSAP (F0F0) can be used to block NetBIOS
and TYPE (6004) can be used to block local-area transport.
Step 5 Modify any filters or access lists that are blocking traffic. Continue
testing filters until all filters are enabled and connections still work.