Odd Network Problem with FC5+

[blake at ispn.net]

I seem to be having trouble sending mail from an FC5 server to
mail.jococourthouse.com.

The problem manifests itself as extreme slowness, which eventually leads
to a timeout before I can even receive a full welcome prompt from the
remote side.

I have tested on ~ 10 boxes (different hardware) around the US ranging
from FC5 through FC8 and NONE can telnet to this mx while RH, FC3 RH4,
windows, and cisco gear on the same networks can ALL telnet without a
problem.

wireshark on the FC5 boxes show that the TCP handshake occurs as normal,
however from then on all I receive from the remote side are 60 byte frames
labeled 'TCP segment of a reassembled PDU' until I eventually receive an
RST from the remote. - A capture on the working boxes looks normal.

I suspect the problem is related to an IP/TCP change in the kernel or
FC5+, however I have no idea what change could have occurred. Any insight
or recommendations for resolving this problem would be appreciated.


Thanks,
-Blake