System information

Troubleshooting Transparent Bridging
Book Title
20-428
Transparent Bridging: Sessions Terminate Unexpectedly
Symptom: Connections in a transparently bridged environment are successfully established, but
sessions sometimes terminate abruptly.
Table 20-2 outlines the problems that might cause this symptom and describes solutions to those
problems.
Table 20-2 Transparent Bridging: Sessions Terminate Unexpectedly
Transparent Bridging: Looping and Broadcast Storms Occur
Symptom: Packet looping and broadcast storms occur in transparent bridging environments. End
stations are forced into excessive retransmission, causing sessions to time out or drop.
Note Packet loops are typically caused by network design problems.
Table 20-3 outlines the problems that might cause this symptom and describes solutions to those
problems.
Table 20-3 Transparent Bridging: Looping and Broadcast Storms Occur
Possible Causes Suggested Actions
Excessive retransmissions
Step 1 Use a network analyzer to look for host retransmissions.
Step 2 If you see retransmissions on slow serial lines, increase the
transmission timers on the host. For information on configuring your
hosts, refer to the vendor documentation. For information on
troubleshooting serial lines, refer to Chapter 15, “Troubleshooting
Serial Line Problems.”
If you see retransmissions on high-speed LAN media, check for
packets sent and received in order, or dropped by any intermediate
device such as a bridge or switch. Troubleshoot the LAN media as
appropriate. For more information, refer to the media
troubleshooting chapter that covers the media type used in your
network.
Step 3 Use a network analyzer to determine whether the number of
retransmissions subsides.
Excessive delay over serial link Increase bandwidth, apply priority queuing, increase the hold queue size, or
modify the system buffer size. For more information, refer to Chapter 15,
“Troubleshooting Serial Line Problems.”
Multiple root bridges If there are multiple root bridges in the network, the root of the spanning tree
can periodically change, causing connections to drop.
Step 1 Use a network analyzer to find out whether there are multiple root
bridges. You can also use the show span exec command on each
bridge to see whether a bridge is a root bridge.
Step 2 If there are multiple root bridges in the network, eliminate the
extraneous root bridges. Use the bridge group priority number
command on root bridges to force the desired bridge to become the
root. The lower the priority, the more likely the bridge is to become
the root.