Re: Help with troubleshooting performance issue

Thanks, James.
I am doing a lab comparing pptp performance and ipsec vpn performance, so
this is not really for production :)

I did tcpdump on the pptp server, I am seeing a few [TCP Previous Segment
not captured] and [TCP ACKed unseen segment].
Not sure what that means though.

The machines are older machines, but they are dual-core machines.
Assuming everything is optimised, are you saying that pptp might not be
able to sustain more than around 6-8MBps traffic?




On Tue, Apr 2, 2013 at 3:39 PM, James Cameron <[email protected]> wrote:

> Capture the data on the PPP interface and analyse it using Wireshark.
> Look for retransmits.  PPTP may be failing to allocate kernel memory
> for socket operations, and it should react by discarding the packet
> rather than trying again.  PPP may be doing something similar.  If
> there is packet loss, the TCP stream will slow down.
>
> PPTP data is handled by a user-space process rather than by the kernel
> alone, and so contention between the SCP and FTP processes and PPTP
> may be cause.  Do the machines have multiple CPUs or only one?
>
> PPTP wasn't originally designed with this I/O rate, so I'm surprised
> you are even getting 4 or 5 MBps.  I have always observed a
> performance degradation with PPTP.
>
> Have you tried OpenVPN yet?
>
> --
> James Cameron
> http://quozl.linux.org.au/
>



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