Fast forward or cut-through switching is the fastest way of forwarding packets thorough a
switch. The switch forwards the packets as soon as the switch is able to determine the
destination MAC address. Although this generally reduces network latency, fast forward
switching doesn't verify the checksum and consequently allows bad packets to pass, which
can reduce the available bandwidth. In fast forward switching the sending direction is never
established which means that two hosts can send to each other simultaneously which will
lead to a collision.
Store and Forward
In Store and forward switching the switch waits until the entire packet is received before
sending it to the destination. This lets the switch verify the packet's checksum and eliminate
the possibility of forwarding bad packets. While the packet is stored in the buffer of the
switch, the transmission direction is established, which means that no collisions can occur.
A disadvantage with store and forward switching is that a delay occurs because the switch
needs time to buffer and analyze the packet.
The fragment free switch works just like fast forward, but it buffers 64 bytes of every
packet in order to avoid collisions.