This article provides more information about the Cyclic Redundancy Check (CRC) or CRC/Align errors that may be observed on switches.

lab@qfx> show interface et-0/2/1 | match "CRC/Align"
Physical interface: et-0/2/1, Enabled, Physical link is Up
CRC/Align errors 29999 0

Cyclic Redundancy Check (CRC) alignment errors or CRC/Align errors occur in digital networks during the process of error detection. CRC is an error-detecting code that is used to detect accidental changes to digital data. CRC alignment errors indicate that there is a problem with the alignment of the received data packets, causing the CRC value to be incorrect. 

CRC errors can be caused by physical issues such as cable problems, issues with the far-end system, or problems with the port or Physical Interface Card (PIC). To resolve CRC alignment errors, physical checks of the ports and layer 1 troubleshooting should be performed to identify and address the underlying issues.

Please follow the below steps to resolve/isolate the issue :

1. Ensure that the cable, smart jack, patch panel, and port are well/tightly connected.
2. Check cable integrity by looking for breaks or other physical abnormalities in the cable.
3. Re-seat the appropriate optic.
4. Check with a known good optic and fiber optic cable and determine if the errors continue to increase.
5. If replacing the optic and cable did not help to resolve the CRC error, use a known good working PIC module in the same slot and check if the errors persist. If the errors stop, then the issue is with the PIC module and you can replace the PIC. Otherwise, the issue is with the chassis and you might have to replace the chassis.

• 2024-03-31 : Initial Publication
• ​​​​​​​2024-07-29 : Visibility modified
• 2024-25-12 : Added few steps to isolate the issue & modified the category
• 2025-11-17: Minor non-technical changes made