[pptp-server] Giving up waiting for packets on LAN?

[Thorvald Natvig]

> > I'm using pptpd-1.1.2 with ppp-2.3.11 on Linux 2.2.19, plus the mppe
> > patches.
> >
> > The VPN link works fine for normal 'low intensity' traffic, but as soon as
> > I start a full speed FTP transfer, the log on the server fills with:
> >
> > May 30 22:23:28 eva pptpd[30516]: Buffering out-of-order packet; got 3178 after 3176
> > May 30 22:23:28 eva pptpd[30516]: Buffering out-of-order packet; got 3179 after 3176
> > May 30 22:23:28 eva pptpd[30516]: Buffering out-of-order packet; got 3180 after 3176
> > May 30 22:23:28 eva pptpd[30516]: Gave up waiting for 1 lost packets beginning with 3177
> ...
>
> > Any ideas on what's wrong and how I can fix it?
>
> Sniff the network and see if that 3177 packet actually crosses the wire.
> At least then you'll know which end of the list to look at more closely.

I've done a bit of ethereal sniffing, and judging by the GRE sequence
numbers, it seems that, indeed, some of the GRE packets from the client
are silently dropped by the router. *Sigh*

But why does a drop rate of 1% reduce the speed by 90%? Is the overhead of
'correcting' the loss that large?