Troubleshooting Guide

 Gigabit Port Configuration
 Common Catalyst Switch Software Issues
 Common NIC Issues and Resolutions
When you troubleshoot NIC issues with Catalyst switches, the first step is to verify that the issue is not
related to a possible configuration issue with the Catalyst switch. For useful information that pertains to
common connectivity issues with the configuration of the Catalyst switch, refer to these documents:
 This document addresses initial connectivity delays that occur when workstations connected to
Catalyst switches are unable to log in to a network domain (Microsoft Windows NT or Novell), or
are unable to obtain a Dynamic Host Configuration Protocol (DHCP) address, due to the Catalyst
switch configuration. The first step in order to troubleshoot these scenarios is to confirm that the
switch configuration is correct, as shown in Using PortFast and Other Commands to Fix
Workstation Startup Connectivity Delays.
 Excessive data link errors cause ports on some Catalyst switches to go into an errdisabled
state. Recovering From errDisable Port State on the CatOS Platforms describes what the
errdisable state is, explains how to recover from it, and provides two examples of recovery from
this state.
Why Do Autonegotiation and Compatibility Issues Exist?
A
utonegotiation issues can result from nonconforming implementation, hardware incapabilities, or
software defects. When NICs or vendor switches do not conform exactly to the IEEE specification 802.3u,
problems can result. Hardware incompatibility and other issues can also exist as a result of vendor-
specific advanced features, such as autopolarity or cable integrity, which are not described in IEEE 802.3u
for 10/100 Mbps autonegotiation. Generally, if both the NIC and the switch adhere to IEEE 802.3u
autonegotiation specifications and all additional features are disabled, autonegotiation must properly
negotiate speed and duplex, and no operational issues exist.
General Troubleshooting for 10/100/1000 Mbps NICs
Autonegotiation Valid Configuration Table
Speed determination issues can result in no connectivity. However, issues with autonegotiation of duplex
generally do not result in link establishment issues. Instead, autonegotiation issues mainly result in
performance-related issues. The most common problems with NIC issues deal with speed and duplex
configuration. Table 1 summarizes all possible settings of speed and duplex for FastEthernet NICs and
switch ports.
Note: This section is only applicable for 10/100/1000 Mbps (1000BASE-T) NICs, and not 1000BASE-X
NICs.
Table 1—Autonegotiation Valid Configuration
Configuration
NIC
(Speed/Duplex)
Configuration
Switch
(Speed/Duplex)
Resulting NIC
Speed/Duplex
Resulting
Catalyst
Speed/Duplex
Comments
AUTO AUTO
1000 Mbps,
Full-duplex
1000 Mbps,
Full-duplex
Assuming
maximum
capability of
Catalyst switch,
and NIC is
1000 Mbps,
full-duplex.
1000 Mbps, Full-
duplex
AUTO
1000 Mbps,
Full-duplex
1000 Mbps,
Full-duplex
Link is
established, but
the switch does
not see any
autonegotiation
information
from NIC.
Since Catalyst
switches
support only
full-duplex
operation with
1000 Mbps,
they default to
full-duplex, and
this happens
only when