Re: mtu/mru problems with pptp

Petko Bordjukov wrote:
> Hi!
> My ISP provides Internet via a VPN so I generally followed this guide
> (http://www.mreriksson.net/howtos/netbsd-pptp-client/) to install a pptp
> client and I also set up a NAT to share the internet connection.
>
> The default options provided by the guide worked well until I tried to
> open www.google.com - the HTTP headers get properly recieved but the
> rest of the page can't be loaded(due to corrupted packets).
>
> After a few hours I found that a change in the mtu/mru options of pptp
> made a difference - at mtu 1000 and mru 1000 google works perfectly but
> guess which site stopped working properly - microsoft.com!
>
> The host that has this problem runs NetBSD 3.0.1 but I tested it also on
> 3.1 and it still persisted. On windows and Linux, however pptp runs
> properly.
>
> Please, help, I ran out of ideas .. :)
>   

Hello,

You are most likely a victim of various clueless net admins
who are filtering out ICMP and thereby breaking path MTU discovery.

This section of the PPPoE guide might be useful for PPTP as well:
http://www.netbsd.org/Documentation/network/pppoe/#clamping

You might need a lower mmsclamp value, though.

-Tobias