@Enzoly wrote: Hello.   I have a problem of Very High proportion of CRC error when I connect a Cisco 7940 phone to my Meraki MS355-24, immediately the port is blocked. I changed several patch cords, but it doesn't work properly. Does anyone have any idea about this error? how can i solve it?   Thank you Common Causes and Solutions: CRC errors can be caused by a number of factors. Typically they are caused by either defective cable, transceiver (SFP), switch port, upstream network device, etc. To address this error, try replacing the cable or transceiver (SFP) and check the switch port and upstream network device. source : IMDB Support ... View more