Switching types and MAC tables

- [Voiceover] Early switches and bridges…used RISK and CISK processing in a method…known as Store and Forward.…SAF will receive a frame in its entirety.…It will then calculate the frame check sequence…for the datagram and ensure it hasn't been corrupted.…If everything checks out, the device…will then forward the frame.…As you can image, on older, slower devices…this wait and send system would cause…additional latency for your traffic.…When switches transitioned to ASICs,…they began using the cut-through method of forwarding.…

In cut-through, a switch will wait…for the portion of the frame header…that lists the destination MAC address,…then forward it on its way.…Since it doesn't store the entire frame,…it incurs much less latency, but also…doesn't check the FCS, so corrupted traffic can be sent on.…When the receiving host is given a bad frame,…its NIC will simply discard it.…At least, this is how cut-through switches used to operate.…Now that they are more intelligent…with even more sophisticated ASICs,…it can read more of the headers if necessary.…