Information Technology Reference
In-Depth Information
Table20-2 Transparent Bridging: No Connectivity (continued)
Possible Causes
Suggested Actions
Bridging filters
are
misconfigured
Use the
show running-config
privileged exec command to
determine whether bridge filters are configured.
1.
Disable bridge filters on suspect interfaces, and determine
whether connectivity returns.
2.
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.
3.
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.
4.
Modify any filters or access lists that are blocking traffic.
Continue testing filters until all filters are enabled and
connections still work.
5.
Input and output
queues are full
Excessive multicast or broadcast traffic can cause input and
output queues to overflow, resulting in dropped packets.
1.
Use the
show interfaces
command to look for input and
output drops. Drops suggest excessive traffic over the media.
If the current number of packets on the input queue is
consistently at or greater than 80 percent of the current size
of the input queue, the size of the input queue may require
tuning to accommodate the incoming packet rate. Even if the
current number of packets on the input queue never seems to
approach the size of the input queue, bursts of packets may
still be overflowing the queue.
2.
Reduce broadcast and multicast traffic on attached networks
by implementing bridging filters, or segment the network
using more internetworking devices.
3.
If the connection is a 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 Lines.”
1.
MAC = Media Access Control
2.
LSAP = link services access point
Transparent Bridging: Unstable Spanning Tree
Symptom
: Transient loss of connectivity between hosts. Several hosts are affected at the same time.
