"Russ Cooper (I think) sent me some configuration suggestions to try on
the NT system to see if it could be make to behave properly in this
>scenario, but I've never had a chance to try them and see if it helps. I'm
>sure I have his message around here somewhere, but I cannot find it right
now. If he sees this, perhaps he'll repeat it to the list."
>Try changing the following entry in your registry and see if this changes
>NT's behaviour with respect to your proxy. I suspect it will.
>Value: EnablePMTUBHDetect REG_DWORD
>Range: 0 or 1
>Default: 0 (false)
>Setting this parameter to 1 (True) causes TCP to try and detect "Black Hole"
>routers while doing Path MTU Discovery. A "Black Hole" router does not return
>ICMP Destination Unreachable messages when it needs to fragment a TCP packet
>with the Don't Fragment bit set. TCP depends on receiving these messages to
>perform Path MTU Discovery. With this feature enabled, TCP will try to send
>segments without the Don't Fragment bit set if several retransmissions of a
>segment go unacknowledged. If the segment is acknowledged as a result, the
>MSS will be decreased and the Don't Fragment bit will be set in future
>packets on the connection. Enabling black hole detection increases the
>maximum number of retransmissions performed for a given segment.
>...running MS Exchange Server 4.0 on NT 4.0, the future is here now.