MAC Frame CRC Errors
This event is triggered when the number of CRC errors per second is higher than the value configured in the Expert Thresholds setup.
These CRC errors are the most common, and are what most devices and analyzers are referring to when they claim a CRC error has occurred. Ethernet packets are encapsulated in a MAC frame that contains a preamble, and a post-envelope CRC check. The Ethernet adapter on the sending station is responsible for creation of the preamble, the insertion of the packet data (addressing, protocol, data, etc.) and then calculating a CRC checksum and inserting this at the end of the packet. The receiving station uses the checksum to make a quick judgment if the packet was received intact. If the checksum is not correct, the packet is assumed to be bogus and is discarded.
MAC frame CRC errors can be caused by a number of factors. Typically they are caused by either faulty cabling, or as the result of a collision. If the cabling connecting an Ethernet Adapter or hub is faulty the electric connection may be on and off many times during a transmission. This "on and off" state can interrupt parts of a transmission, and "damage" the signal.
If a collision happens during packet transmission, the signal for the specific packet will be interrupted, and the resulting received packet will be damaged.
If the signal is interrupted partially during transmission, the CRC checksum that was calculated by the network adapter will no longer be valid and the packet will be flagged as a CRC error and discarded.
CRC errors are common on a busy network, and a small percentage does not reflect a network problem. When the percentage is large, or when a single station shows a larger percent CRC errors there is probably a problem that needs to be addressed.