[pptp-server] Severe performance problems

[George Vieira]

Yes this sounds true but rememeber alot of people having speed problems have
switched off encryption and it still made no difference so that can't be the
problem.


thanks,
George Vieira
Systems Manager
Citadel Computer Systems P/L


-----Original Message-----
From: Charlie Brady [mailto:charlieb at e-smith.com]
Sent: Thursday, 13 December 2001 3:00 AM
To: Gianluca Insolvibile
Cc: pptp-server at lists.schulte.org
Subject: Re: [pptp-server] Severe performance problems



On Wed, 12 Dec 2001, Gianluca Insolvibile wrote:

> I have seen the recent thread on the 'speed' option, but I am not
> using that. In my case, I suspect something strange is happening with
> TCP flow control over the PPTP channel, but just can't imagine what.

An interesting theory indeed.

A google search for "nagle tcp" reveals a number of possibilities,
including:

http://www.icase.edu/coral/LinuxTCP.html
http://support.microsoft.com/default.aspx?scid=kb;EN-US;q235624


The key negotiation for MPPE might introduce significant latency, and that
could affect the TCP transmission and retransmission timers.

Remember too that PPTP packets must come in off the wire, go through the
kernel, then into pptpd, then through the kernel and into pppd, then back
through the kernel and into the application on the server. And vice versa
on the way back out to the client.

All this adds up to quite a lot of processing. Add to that 3DES
encryption/decryption for each packet.

Charlie Brady                         charlieb at e-smith.com
Lead Product Developer
Network Server Solutions Group        http://www.e-smith.com/
Mitel Networks Corporation            http://www.mitel.com/
Phone: +1 (613) 368 4376 or 564 8000  Fax: +1 (613) 564 7739


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