[svlug] Re: Re: TCP checksum ignored?

Ira Abramov lists-svlug at ira.abramov.org
Sun Mar 23 12:42:30 PST 2003


Quoting J C Lawrence, from the post of Sun, 23 Mar:
> > so what can corrupt the data but keep it looking correct on the way
> > from the eth0 interface to the kernel?
> 
> Hurm.  Is it always the same corruption?  

that would require a lower level disection of how patterened info looks
after corruption, but as a friend on another LUG list just told me, TCP
uses a crappy 16 bit checksum that is about as good as crc10, not as
good as crc32. what's worse, is that checksum algorithems of this type
are not good at detecting failures that flip the same bit in repeating
bytes. i.e. always screwing the 3rd bit of every 16 bit block of the
stream may not get detected by the checksum, as it was designed to
detect errors in noisy comm lines (random errors), not bad buffer memory
register bits (consistent errors).

Does this make sense? :)

Night,
Ira.

-- 
Supreme being of leisure
Ira Abramov
http://ira.abramov.org/email/



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