It looks like I've found a "fix" (workaround is still a better name).
I've changed the part that generates the mpd config files in
/etc/inc/interfaces.inc to add the following options:
set iface enable tcpmssfix
And to mpd.links:
set pptp disable delayed-ack
Until now, this seems to work for me, but since the problem is hard to
reproduce, it's too early to draw any permanent conclusions.
It would be nice if others that are having similar problems could try if
it fixes their problems as well.
The modified file can be downloaded from http://www.xs4all.nl/~fredmol/m0n0/.
It's distributed as a tgz file. It can be included in a m0n0wall image
by using the module installer, available from the same location.
Alternatively, it can be used to update a running m0n0wall system:
- navigate to <m0n0wallip>/exec.php
- upload wan-pptp-opts.tgz
- execute "(cd /; tar xvfz /tmp/wan-pptp-opts.tgz)" (excluding quotes)
- navigate to the WAN setup page and press "Save". This will restart mpd,
with the extra mpd options.
Note that these changes will be gone after a reboot.
Also note that the modified file is for m0n0wall 1.11b16.