What is CRC Stomping

Facts

Cisco Nexus or UCS cut-through switches

Answer

The Frame Check Sequence (FCS) is a 4-byte (32-bit) trailer added to the end of every ethernet frame.
The originator of the frame calculates a cyclic redundancy check (CRC) code against the frame it is sending, and sends this CRC code as the frame FCS trailer.
The receiver verifies the received CRC code against received frame.

Nexus switches (including UCS Fabric-Interconnects and IOMs) are cut-through switches.
This means that as soon as the switch receives a frame, it reads the destination MAC address and starts forwarding the frame to the destination.
At the end of the frame it performs the frame check sequence (FCS) calculation to check if the frame is corrupted.
If the frame is found to be corrupted it is too late to drop it, as it is already being forwarded to the destination.

So to mark the frames as corrupted the switch will STOMP the frame. That means that it writes a well-known sequence into the FCS at the tail of the frame that identifies this frame as being corrupted.
Also a counter will be incremented to say that an interface received a frame with a CRC error that was not STOMPED already (RX_CRC_NOT_STOMPED)

The corrupt (STOMPED) frame will be forwarded to the next device on the route to the destination. If the next device is a cut-through switch it will see that the frame was already STOMPED and so it will increment a counter to say that it received an already STOMPED frame (RX_CRC_STOMP)

The frame will continue to the destination until it reaches a store-and-forward switch or an end-device such as a server which will drop it.