Rockwell Automation Publication 1783-UM003G-EN-P - December 2012 143
Troubleshoot the Switch Chapter 5
Switch Performance
Following are some basic troubleshooting for issues related to switch
performance.
Switch Performance
Issue Resolution
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 indicate a speed or duplex mismatch.
A common issue with speed and duplex occurs when the duplex settings are mismatched between
two switches, between a switch and a router, or between the switch and a workstation or server. This
can happen when manually setting the speed and duplex or from autonegotiation issues between the
two devices. A mismatch occurs under these circumstances:
• A manually set speed or duplex parameter is different from the manually set speed or duplex
parameter on the connected port.
• A port is set to autonegotiate, and the connected port is set to Full-duplex with no autonegotiation.
To maximize switch performance and be sure of a link, follow one of these guidelines when changing
the settings for duplex and speed:
• Let both ports autonegotiate both speed and duplex.
• Manually set the same speed and duplex parameters for the ports on both ends of the connection
to the same values.
• If a remote device does not autonegotiate, configure the duplex settings on the two ports to the
same values.
The speed parameter can adjust itself even if the connected port does not autonegotiate.
Autonegotiation and network interface cards
(NICs)
Issues sometimes occur between the switch and third-party network interface cards (NICs). By
default, the switch ports and interfaces are set to autonegotiate. It is common for devices like laptops
or other devices to be set to autonegotiate as well, yet sometimes autonegotiation issues occur.
To troubleshoot autonegotiation issues, try manually setting both sides of the connection. If this does
not solve the issue, there could be an issue with the firmware or software on your NIC. You can
resolve this by upgrading the NIC driver to the latest version available from the manufacturer.
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.
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