At 10:26 19/12/2006, Randall Stewart wrote:
I have always thought of it as a bit of a hack as well... and there is one really big problem with it.. It has no value unless you can tell your network-interface card to deliver damaged packets. I don't know if some cards have this option now or not.. nor if an API in any driver exists for it... without this you will find very very few packets that are "damaged" that do get through.. since generally the link layer checksum is a MUCH better CRC vs the very weak IP/UDP checksum :-0
Each check is meant to detect a different type/source of errors. The CRC is meant to detect burst errors, which are lokely to occur due to, eg, noise. OTOH, the checksum is meant to detect single bit errors, which are more likely to occur in the memory of the processing systems.
There'sa paper by Stone and Partridge (in ACM's CCR) in which they show errors that, IIRC, were not caught by the CRC, but *were* caught by the checksum.
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