Norman Wilson norman at oclsc.org
Sat Sep 14 08:01:14 AEST 2019

Peter Jeremy:

> NFS ran much faster when you turned off the UDP checksums as well.
> (Though there was still the Ethernet CRC32).

Dave Horsfall:

  Blerk...  That just tells you that the packet came across the wire more or
  less OK.


UDP (and TCP) checksums are nearly useless against
the sort of corruption Larry described.  Since they
are a simple addition with carry wraparound, you
can insert or remove any number of word-aligned pairs
of zero octets without the checksum changing.

I discovered this the hard way, while tracking down
a kernel bug that caused exactly that sort of corruption.

Does IPv6 require a meaningful checksum, or just the
useless old ritual one?

Norman Wilson
Toronto ON

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