Cisco Catalyst 5000 Series Switches

Field Notice: Troubleshooting Loss of Connectivity to Network and Increasing FCS Errors With Gig E Uplink Module Connection on a Catalyst 5x00 With a Supervisor III or Supervisor IIG

September 11, 2001

Products Affected


Top Assembly

Printed Circuit Assembly


HW Rev.

Part Number


Part Number







Dual Port 1000BASE-SX-MMF Uplink Module







Dual Port 1000BASE-LX/LH-MMF/SMF Uplink Module


Problem Description

Loss of connectivity to the network or outages with increasing frame check sequence (FCS) errors with a Gig E Uplink module connection on a Catalyst 5x00 series switch with a Supervisor III or Supervisor IIG.Background

This document describes the troubleshooting procedure recommended by the Cisco Technical Assistance Center (TAC) and Network Supported Accounts (NSA) for the Gig E Uplink module in the Catalyst 5x00 series with a Supervisor III or Supervisor IIG. The uplink modules are commonly configured as trunk ports connecting to other Catalyst switches or third party devices.

Problem Symptoms

The following symptoms may be seen when experiencing a loss of connectivity to the network, or by network management systems as an alert:

Note:?Not every single circumstance may necessarily fit these symptoms.

  1. The link coming to or from an uplink module to another uplink module shows to be up and connected on both sides. However, no traffic is actually passing over the link.

  2. One side of the link shows increasing FCS errors (these may be alignment errors in some cases). The number of errors depends on how long the problem has been happening. Typically, the accrual of errors is fairly rapid.

  3. One side of the link can see the Cisco Discovery Protocol (CDP) neighbor on the other side of the link, but the reverse is not true.


These troubleshooting guidelines can help to identify misconfigurations, bad cabling or other system problems. These problem symptoms can be due to duplex mismatch, bad hardware (network interface card [NIC], cable or port), or a connected device generating frames with bad FCS. To determine the source of the problem, follow the troubleshooting procedure recommended by the Cisco TAC and NSA for the Gig E Uplink module in the Catalyst 5x00 series with a Supervisor III or Supervisor II G. Please note that you must do this on both sides of the link:

Troubleshooting Guidelines

  1. Make sure the port LEDs indicate that there is both a link and activity.

    • If not, verify if the cable connection is firm.

    • If yes, use the show port command to verify if the port is receiving any physical-layer (alignment and FCS) errors.

    • If the FCS error count is increasing - which may be the result of a duplex mismatch, bad hardware (NIC, cable, or port), or a connected device generating frames with bad FCS - perform a clear counters operation and start logging the output to a file. Then perform the following commands three times:

      • show time

      • show counters <module/port>

      • show asicreg <module/port> gigmac

      • show ascireg <module/port> gigmac_phoenix

      Take a note of results from these commands and proceed to the next step. The show asicreg commands need to be decoded by the TAC.

  2. Troubleshoot the trunk and port:

    • Make sure that the CDP neighbor is seen on the appropriate ports if CDP is enabled on both sides of the link. Use the show cdp neighbor <module/port> command to get details.

    • Make sure that duplex is set to full and the flow control is consistent - these are 1000Base-full duplex ports only. Use the show port command on the switch. Use the show interface command on the router.

    • Verify that trunking is consistent on both sides of the link. This assumes that the link is a trunk. If so, the recommended trunking mode is desirable > desirable switch to switch, or on > on switch to non-DTP device.

    • Make sure that the trunk encapsulation type configured on both ends of the link is valid (use the show trunk command).

    • Make sure that the port is trunking, and that the allowed VLAN list allows the desired VLAN range to pass through (use the show trunk command).

    • On IEEE 802.1Q trunks, make sure that the native VLAN is the same on both ends of the trunk (use the show trunk command).

  3. If, after performing steps 1 and 2, the uplink is still not functioning properly, soft reset the port as follows:

    • Set port <module/port> disable.

    • Set port <module/port> enable.

    • If the uplink is still non-operational, perform a reset.

      Note:?This command causes a Supervisor failover and may affect users connecting to this switch.

  4. If the problem persists, contact the Cisco TAC to open a TAC case and attach the log to the case notes.

The Cisco TAC will review log results and the troubleshooting steps to determine cause of the problem, and will setup an RMA if required. Before Cisco TAC engineers can issue an RMA for the replacement, you should carry out the troubleshooting procedure in this field notice and allow the TAC to verify it.

Additional Information

Providing the following additional information can help the TAC to determine the cause of the problem:

  • What is the Gig E uplink module connected too?

  • How long has this module been installed?

  • How is the fiber physically connected (for instance, by direct run, patch panels or dwdm)?

For More Information

If you require further assistance, or if you have any further questions regarding this field notice, please contact the Cisco Systems Technical Assistance Center (TAC) by one of the following methods: