fragmentfree

Fragment-free is a forwarding mode used in Ethernet switches. It sits between store-and-forward and cut-through in terms of latency and error checking. In fragment-free operation, the switch begins to forward a frame after it has read the destination MAC address and after at least the first 64 bytes of the frame have been received. This approach reduces the likelihood of forwarding a fragment caused by a collision on half-duplex Ethernet, while avoiding the full-frame buffering required by store-and-forward.

Compared with cut-through, fragment-free adds a minimal delay to guarantee that frames are not fragments; compared with store-and-forward, it does not wait for the entire frame to be error-checked, so it cannot guarantee CRC correctness before forwarding. Consequently, fragment-free is most relevant on networks that still operate in half-duplex or where legacy compatibility matters. With the decline of CSMA/CD in modern switched Ethernet and the move to full-duplex networks, fragment-free has become less common; many current devices either default to store-and-forward or implement other low-latency forwarding schemes.

See also: cut-through switching, store-and-forward switching, CSMA/CD.