Troubleshooting CRC Errors on Gigabit Ethernet Interfaces


The CRC counter continues to increment, as shown in the show interfaces gig output:

Force10>show interface gig 0/7
GigabitEthernet 0/7 is up, line protocol is up
Hardware is Force10Eth, address is 00:01:e8:07:e0:00
SFP present. Media type is ZX.
Internet address is not set
MTU 1554 bytes, IP MTU 1500 bytes
LineSpeed 1000 Mbit
ARP type: ARPA, ARP Timeout 04:00:00
Last clearing of "show interface" counters 13w5d19h
Queueing strategy: fifo
     51040098567 packets input, 12649732603754 bytes
     Input 50484710883 IP Packets, 50872183339 Vlans 0 MPLS
     21293513947 64-byte pkts, 16911511032 over 64-byte pkts, 1131757544 over 127-byte pkts, 2803601459 over 255-byte pkts, 5251066555 over 511-byte pkts, 3648648031 over 1023-byte pkts Received 0 input symbol errors, 0 runts, 0 giants, 0
throttles, 12783 CRC, 0 IP Checksum, 0 overrun, 0 discarded
     65507855048 packets output, 50346845285803 bytes, 0 underruns
     Output 236700899 Multicasts, 1389966414 Broadcasts, 63881187735 Unicasts

Background / Explanation

The following issues have been shown to generate CRC errors:

  • Bad fiber cable
  • Dirty optics
  • This condition has been seen when a connected router interface, with auto-negotiation disabled, was shut down without a link-down being detected by the Force10 system. Some third-party devices continue to power on the fiber port’s laser even though the port is in shutdown mode.

Troubleshooting Steps

To troubleshoot a bad fiber cable, try reducing the attenuation.

To troubleshoot dirty optics, clean the optics at both ends, as described in Cleaning and Inspecting Optical Fibres.

Try a different fiber cable and try connecting it to different ports.

Information to Collect if You Open a TAC Case

If you still would like assistance from Force10 Networks after following the troubleshooting steps above, please use the Create Service Request form on the isupport page and include the following information if available:

  • Console captures showing the error messages
  • Console captures showing the troubleshooting steps taken and the boot sequence during each step
  • Saved messages to a syslog server, if one is used.
  • Output from the show trace command
  • Output from the show tech-support command