[pptp-server] PPTPD works great on LAN ! Half-Life/Q2 almost works over dial-up...

Patrick J. LoPresti patl at cag.lcs.mit.edu
Mon Dec 20 16:53:56 CST 1999


"Patric Sandberg" <patric.sandberg at swipnet.se> writes:

> The thing is; when running over the Internet with a Win98SE VPN
> client using a 33.6 outgoing stream from a 56k modem things get
> hairy when loading the tunnel; running Quake2 drops the tunnel after
> a few minutes, Half-Life too.

> I get an error message in the /var/log/messages about GRE dropping
> 'out of sequence' packets. Does anyone run PPTPD over slow dial-up
> links successfully?

(Warning: I am relatively new to this stuff, so everything below might
be nonsense.)

We are trying to deploy PoPToP as a serious solution, which means
working well over high-latency and low-bandwidth links.  We are still
in the experimental phase, so I don't really have any concrete
suggestions for you.

What I have done so far is to rewrite pptpgre.c to support windowing.
Adaptive timeouts and window sizing will be next; I am conversing with
the PoPToP experts to get their ideas on approaches to use.

The other thing I want to try is playing with the mru/mtu size in
pppd.  (By the way, doesn't PPTP completely screw over path MTU
discovery?  I mean, the apparent end-to-end MTU will be independent of
the MTUs along the path of the GRE tunnel, creating "hidden"
fragmentation which could be really bad for TCP?)

I am really interested in getting this sorted out, but I can probably
only work on it on weekends, so it may take some time unless some
other hackers show interest...

 - Pat




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