In message <200204292035.g3TKZ9c15253@marajade.sandelman.ottawa.on.ca>,
Michael Richardson writes:

[..]

>    Sean> (tcpdump -w x -vvv -s 1500 -i en0 -ttt host world; tcpdump -r x
>    Sean>  yeah, station-a is a mac os x laptoy...).
>
>  I can't really see anything wrong there... with -vvv it should be checking
>the TCP checksums, so they are okay.... There isn't any NAT occuring on
>"router" is there?

If you're looking for bad-cksum indications, you want the -vvv on the
pretty-printer side, not the data-collection (capture) side.
Something like:

   (tcpdump -w x -s 1500 -i en0 ip host "host" and ip host "world"; tcpdump -r x -vvv  -ttt)

mutatis mutandis, for anything different from Sean's original.
Then again, perhaps it was just a glitch in transcription.