>> 	router 1 was broken from DF bit manipulation.  it behaved like this:
>> 	- if DF bit is raised on a packet, it worked fine.  it transmits
>> 	  icmp "too big" as necessary toward source, if the source node sends
>> 	  1500byte-packets.
>> 	- if DF bit is off, it behaved wrong.  if the source node sends
>> 	  1500byte-packets, it drops the packet onto the floor.  router 1
>> 	  should have fragmented the packet on its own and relay it to router 2
>> 	  (VLAN side), but it did not.
>My "router 1" is my 486/66 NetBSD-1.4V machine with a GIF tunnel, and it
>does appear to successfully send fragmented packets, and most remote
>systems do recieve those fragmented packets sucessfully and they
>apparently reassemble them without problems.
>
>Other than that though your observations do appear to match my own.

	don't you have any other (not-administered-by-you) device in the middle?
	when i read your original posting my impression was that you are
	having problem with SMTP, to far-away peers.... anyway, you may want to
	gather as much tcpdump traces as you can, and cross-check these to see
	anyone is behaving strange.

itojun