On Sun, Apr 15, 2001 at 07:55:17AM -0400, Andrew Brown wrote:
> >I have a problem connecting to a pop3 server when connected over PPPoE
> >(MTU 1492), while everything works using an ISDN connection (MTU 1500).
> >
> >I get bad tcp cksums for fragmented packets.
> 
> off the top of my head, i'd say that you should expect to.  fragments
> are necessarily incomplete so the total checksum will be not
> calculable.

More to the point, only the first fragment *contains* the checksum.
This is never expected to work, and tcpdump probably shouldn't even
try.