Full Answer: CRC errors Cisco networking CRC errors are generally at layer 1 issue caused by a faulty port on the device or bad Ethernet cable. Changing the cable or swapping the port is a relatively easy fix. <> Occasionally they are generated on layer 2 by a duplex mismatch. This happens when the port on one device is set for full-duplex and the port on the connected peer device is set for half-duplex. The ports can be compared by using the show interface command on both devices, to see speed and duplex. <> In TDM networks, there are many problems that cause CRC errors. They include faulty wiring or cross-connects, bad repeater cards, flakey smart jacks, or bad cable and channel cards. Isolating the cause of these errors usually requires the telecommunications provider to conduct loopback testing or to dispatch a field engineer to the site to test head-to-head with the central office. <> Personal computers receive CRC error messages when they are reading files and detect corrupt data. Bad hard drive sectors, scratched or dirty external media, loose wiring inside the computer and faulty external drives or buggy software are all potential causes. Troubleshooting procedures to isolate the cause of the errors include cleaning the DVD, reloading or updating software programs, performing hardware diagnostic tests and possibly replacing external drives.