Cisco 2975 - Manual (Page 42)

3-4
Catalyst 2975 Switch Hardware Installation Guide
OL-17784-01
Chapter 3 Troubleshooting
Clearing the Switch IP Address and Configuration
Loops can be caused by a unidirectional link. A unidirectional link occurs whenever the traffic sent by
the switch is received by its neighbor, but the traffic from the neighbor is not received by the switch. A
broken fiber-optic cable, other cabling, or a port issue could cause this one-way communication.
You can enable UniDirectional Link Detection (UDLD) on the switch to help identify unidirectional link
problems. For information about enabling UDLD on the switch, see the “Understanding UDLD” section
in the switch software configuration guide on Cisco.com.
Switch Performance
Speed, Duplex, and Autonegotiation
If the port statistics show a large amount of alignment errors, frame check sequence (FCS), or
late-collisions errors, this might mean a speed or duplex mismatch.
A common issue with speed and duplex is when the duplex settings are mismatched between two
switches, between a switch and a router, or between the switch and a workstation or server. Mismatches
can happen when manually setting the speed and duplex or from autonegotiation issues between the two
devices.
To maximize switch performance and to ensure a link, follow one of these guidelines when changing the
duplex or speed settings.
• Let both ports autonegotiate both speed and duplex.
• Manually set the speed and duplex parameters for the ports on both ends of the connection.
• If a remote device does not autonegotiate, set the same duplex settings on the two ports. The speed
parameter adjusts itself even if the connected port does not autonegotiate.
Autonegotiation and Network Interface Cards
Problems sometimes occur between the switch and third-party Network Interface Cards (NICs). By
default, the switch ports and interfaces are set to autonegotiate. Devices like laptops or other devices are
commonly set to autonegotiate, yet sometimes autonegotation issues occur.
To troubleshoot autonegotiation problems, try manually setting both sides of the connection. If this does
not solve the problem, there could be a problem with the firmware or software on your NIC. You can
resolve this by upgrading the NIC driver to the latest available version.
Cabling Distance
If the port statistics show excessive FCS, late-collision, or alignment errors, verify that the cable distance
from the switch to the connected device meets the recommended guidelines. See the
“Cables and
Adapters” section on page B-3 for cabling guidelines.
Clearing the Switch IP Address and Configuration
If you have configured a new switch with a wrong IP address, or if all of the switch LEDs start blinking
when you are trying to enter Express Setup mode, you can clear the configured IP address. The switch
returns to the factory default settings.