Cisco Systems 17053 appendix Sniffer Trace

2In−Discard and Lrn−Discard do not exist on all Catalyst platforms.

Table 5￿Possible Causes for Incrementing CatOS Counters

Counter	Possible Cause
Delay Exced	Severe problem with the switch. Create a service
	request with Cisco Technical Support.
	Verify ISL and dot1q configurations. Verify
MTU−Exced	another switch or router does not inject frame
	over maximum transmission unit (MTU) into the
	switch network.
	Increments when the switch receives traffic on a
Lrn−Discard	trunk for a specific VLAN while the switch does
2	not have any other ports on that VLAN. Counter
	also increments when the destination address of
	the packet is learned on the port on which the
	packet is received.
Lrn−Discard	This counter must remain at zero. If counter
2
	increments, create a service request with Cisco
	Technical Support.
In−Lost	Excessive input rate of traffic.
	Excessive output rate of traffic. Increments in this
	counter are more likely to occur when connected
Out−Lost	to low−speed devices. The first step to
	troubleshoot Out−Lost increments is to verify the
	link partner runs 100 Mbps, full−duplex without
	any errors.

2In−Discard and Lrn−Discard do not exist on all Catalyst platforms.

Additional counter information can be viewed with the command show counters mod/port . The command must be issued for a single port at a time. Refer to this document for information on the counter displayed:

∙show counters Command Documentation

For additional information about the Cisco IOS Software show interfaces command counters, refer to:

∙show interfaces Command Documentation

Sniffer Trace

Sniffer trace analysis can be very useful when you troubleshoot switch and NIC performance or connectivity issues when the issues persist after all other sections of this document are reviewed. Sniffer trace analysis reveals every packet on the wire and pinpoints the exact problem. It can be important to obtain several sniffer traces from different ports on different switches. Generally, it is very useful to monitor or span ports rather than spanning VLANs when you troubleshoot switch and NIC performance and connectivity issues.

Refer to Catalyst Switched Port Analyzer (SPAN) Configuration Example for more information on the use of the Switched Port Analyzer (SPAN) feature required to obtain sniffer traces.