Troubleshooting Guide

2
In-Discard and Lrn-Discard do not exist on all Catalyst platforms.
A
dditional 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.
Teaming of Network Interface Cards
Teaming of Network Interface Cards, or NIC Teaming, can cause instability in the networks. Such setups
can introduce disruptions to the Spanning tree and can make it undergo frequent recomputations. If
intermittent loss of connectivity to NIC teamed servers occurs for devices or hosts in the same VLAN, try
to disable NIC teaming. If the connectivity stabilizes, refer to the NIC vendor documentation in order to
tune the NIC teaming configuration.
Use one of these methods in order to implement NIC teaming:
 Server Virtual Address (SVA): The SVA is used when you want other devices in the network to
see the teamed NICs as one physical device with one MAC address. When you use this setup, you
must have one of the NICs in a standby state, and the other in active state. Otherwise, you would
experience duplicate MAC addresses sent around the network from the SVA.
 Separate NIC MAC Addresses: In this setup, you can use both of your NIC cards that run
separate MAC addresses. In this mode, both NICs appear from a network perspective to be two
separate physical devices. You can configure the Fault Tolerant Mode with Load Balancing option
in order to avoid the problem of duplicate MAC addresses on the network.
Additional Troubleshooting for 1000BASE-X NICs
Gigabit Autonegotiation (No Link to Connected Device)
Gigabit Ethernet has an autonegotiation procedure that is more extensive than what is used for 10/100
Mbps Ethernet (Gigabit autonegotiation specification IEEE 802.3z-1998). The Gigabit autonegotiation
negotiates flow control, duplex mode, and remote fault information. You must either enable or disable link
negotiation on both ends of the link. Both ends of the link must be set to the same value or the link does
not connect.
If either device does not support Gigabit autonegotiation, disable Gigabit autonegotiation in order to force
the link up. The default configuration of all Cisco switches is autonegotiation-enabled. If you disable
autonegotiation, it hides link drops and other physical layer problems. Only disable autonegotiation to end-
devices, such as older Gigabit NICs that do not support Gigabit autonegotiation. Do not disable
autonegotiation between switches unless absolutely required, as physical layer problems can go
undetected and result in spanning tree loops. Rather than disable autonegotiation, you can contact the
vendor for a software or hardware upgrade for IEEE 802.3z Gigabit autonegotiation support.
Table 6—Gigabit Autonegotiation Configuration Table
Technical Support.
In-Lost Excessive input rate of traffic.
Out-Lost
Excessive output rate of traffic. Increments in this
counter are more likely to occur when connected
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.