Switching - cut through

Cut through switching, also known as cut through forwarding, is a layer 2 switching method where a switch begins forwarding the frame before the whole frame has been received. This is usually done as soon as the destination MAC address is read, and the outgoing interface is determined.

The advantage of such switching is a decrease in latency. The disadvantage is that no error checking can take place on the frame using the Frame Check Sequence (FCS), since transmission of the frame has already begun before the FCS has been received and checked. Thus, error checking and error handling must be performed by the destination device and not the transient device.

Note that in the Ethernet Header the destination MAC address is the first field that is received, after the preamble and SFD, thus making cut through switching as efficient as possible.

Compare this to Store and forward switching methodology.