Fragment free is a switch forwarding method. Fragment free will ensure that enough bytes are read from the source to detect a collision before forwarding. This is only useful if there is a chance of a collision on the source port - so a fully switched network may not benefit from fragment free in comparison to low latency cut through switching. Frames are forwarded before any checksums can be calculated.
This technique can be thought of as a compromise between the high latency / high integrity of store and forward, and the low latency / reduced integrity of cut through switching.
