>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.

	do you have control over the pop server?  if so, try taking tcpdump
	on both sides and compare the outputs.  i guess there's a intermediate
	device (NAT router?) which is damaging packets.

itojun