Why does Fragment-Free Switching only check the first 64 bytes?

• A. To reduce memory usage
• B. To speed up processing
• C. It is mandated by standards
• D. This is where fragmentation is most likely

Answer: (D)

Fragment-free switching sits between faster cut-through and full store-and-forward, aiming to forward quickly without sending frames that are likely to be corrupted by a collision. The key timing here is tied to how Ethernet CSMA/CD works: the minimum Ethernet frame size is 64 bytes, and a collision must be detectable within the time it takes to transmit those 64 bytes. If a collision happens, the frame would be broken up and the remainder would be invalid. By waiting until the first 64 bytes of a frame have been received before forwarding, the switch can determine the destination and ensure that a frame unlikely to be valid (due to a potential collision-caused fragment) isn’t sent onward.

So, the first 64 bytes is the safe cutoff point: it’s the part of the frame where fragmentation from a collision would already become apparent, making it the most relevant place to check.