Information Technology Reference
In-Depth Information
If the status light on the switch is flashing orange, this usually means that there is some kind of hardware
problem with the port or the module or the switch. The same thing is true if the port or module status
indicates “faulty.”
Before exchanging the switch hardware, you might try a few things:
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Reseat the module in the switch. If you do this with the power on, make sure that the module is
hot-swappable. If in doubt, turn off the switch before reseating the module, or refer to the hardware
installation guide. If the port is built into the switch, ignore this step.
•
Reboot the switch. Sometimes this causes the problem to disappear; this is a workaround, not a fix.
•
Check the switch software. If this is a new installation, remember that some components may work
with only certain releases of software. Check the release notes or the hardware installation and
configuration guide for the component you are installing.
•
If you are reasonably certain that you have a hardware problem, then replace the faulty component.
Troubleshooting Ethernet 10/100-Mb
Half-/Full-Duplex Autonegotiation
This section presents general troubleshooting information and a discussion of techniques for
troubleshooting Ethernet autonegotiation.
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This section shows how to determine the current behavior of a link. It goes on to show how users
can control the behavior, and it also explains situations when autonegotiation will fail.
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Many different Cisco Catalyst switches and Cisco routers support autonegotiation. This section
focuses on autonegotiation between Catalyst 5000 switches. However, the concepts explained here
can be applied to the other types of devices.
Introduction
Autonegotiation is an optional function of the IEEE 802.3u Fast Ethernet standard that enables devices
to automatically exchange information over a link about speed and duplex capabilities.
Autonegotiation is targeted at ports, which are allocated to areas where transient users or devices connect
to a network. For example, many companies provide shared offices or cubes for account managers and
system engineers to use when they are in the office rather than on the road. Each office or cube will have
an Ethernet port permanently connected to the office's network. Because it may not be possible to ensure
that every user has either a 10-Mb, a 100-Mb Ethernet, or a 10/100-Mb card in their laptops, the switch
ports that handle these connections must be capable of negotiating their speed and duplex mode. The
alternative would be to provide both a 10-Mb and a 100-Mb port in each office or cube and then label
them accordingly.
Autonegotiation should not be used for ports that support network infrastructure devices such as
switches and routers, or other nontransient end systems such as servers and printers. Although
autonegotiation for speed and duplex is normally the default behavior on switch ports that are capable
of it, ports connected to fixed devices should always be configured for the correct behavior rather than
allowed to negotiate it. This eliminates any potential negotiation issues and ensures that you always
know exactly how the ports should be operating. For example, a 10/100BaseTX Ethernet
switch-to-switch link that has been configured for 100 Mb full-duplex will operate only at that speed and
mode. There is no possibility for the ports to downgrade the link to a slower speed during a port reset or
a switch reset. If the ports cannot operate as configured, they should stop passing any traffic. On the other
