can not set mtu on tun0 via ppp, mssfixup not working

[tias_(_at_)_tiasarea_(_dot_)_org]

Hi all,

i`ve been looking into this problem for some time now and i have no clue
on what happens ....
symptoms:
i run obsd 3.0 on pentium 166
i have adsl and connect via pppoe
i nat on my internal net
the mtu on tun0 is set to 1500 by default
i have in my /etc/ppp/ppp.conf in a pppoe profile:
set mtu 1492
enable mssfixup
(i tried also set mru 1492
having set mtu max 1492 and/or set mru max 1492 make ppp unusable,
no ip is assigned to tun0)

on the obsd box,
if i ifconfig tun0 mtu 1492
then i can access www.pt.lu with lynx (with mtu 1500 i can not)
but on the internal net no client can access www.pt.lu
(except via a telnet cession, which makes this problem
so strange to me ( i get the page after a GET / HTTP/1.0))

so could someone tell me what is going on ?
i read a lot on this problem and the fix is to add a line that
i already have in my config file. the mtu is stuck to 1500 if
i do not ifconfig the tun...
also what about the mssfixup ?
it should handle the problem on the internal net, isn`t it ?

any help much appreciated

tias

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