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Re: [Openvpn-users] LJ's "cons" of OpenVPN: how serious is latency?

  • Subject: Re: [Openvpn-users] LJ's "cons" of OpenVPN: how serious is latency?
  • From: Florin Andrei <florin@xxxxxxxxxxxxxxx>
  • Date: Tue, 21 Dec 2004 15:47:24 -0800

On Tue, 2004-12-21 at 13:48 -0800, J. Perkins wrote:

> http://www.linuxjournal.com/article/7949
> I'm just wondering how important these considerations are in practice.
> When
> somebody says OpenVPN is "relatively slow", is that "slow" in an
> academic, computer-science inefficient inter-process communication sort
> of way, or slow in a my-users-will-complain sort of way? (And what
> "fast" VPN method are we comparing this to, anyway? IPSec?)

The former.

See today's article on Slashdot about WiFi and PPTP - there's a guy
commenting that he tried to setup an IPSec VPN (was it OpenSWAN? i don't
remember) and he couldn't descend below 150ms latency - definitely not
enough to play some network games.
With OpenVPN he got 50ms which is more than enough for pretty much all

The implementation matters a lot, not just the design. OpenVPN seems to
have an excellent implementation. I'm not judging from a code analysis
standpoint, but from a plain user's.

> Judging by the raves OpenVPN gets on this list for both performance and
> reliability, I wonder how big a deal this is. I considered the LJ
> writer might be over-stating the case

He's overstating.
The only serious defficiency of OpenVPN is that there is no "enterprise"
class solution based on it, so large companies may not consider it.
Otherwise, it's better than most IPSec-based VPNs on pretty much any

> In a related note, would there be any benefit to using a WRAP w/a VPN
> Mini-PCI card for crypto help? Again, I'm going to be limited in
> throughput by the cable connections, so latency is my only concern.

My OpenVPN server is an AthlonXP 1900. My typical client is a 2.6GHz
Pentium M laptop. Even at full-speed transfer of large files over
802.11g, even with compression turned on at all times (non-adaptive
compression), the CPUs barely blink, and the latency does not seem to be
bigger than without VPN (i didn't do benchmarks, but it seems pretty

I've heard about people running VoIP over OpenVPN - that's the mother of
all latency-sensitive applications. They say it works very well.

Florin Andrei


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