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RE: [Openvpn-users] Re: Odd Tunnel Problems


  • Subject: RE: [Openvpn-users] Re: Odd Tunnel Problems
  • From: "James Yonan" <jim@xxxxxxxxx>
  • Date: Fri, 10 Oct 2003 23:38:34 -0000

Erik Anderson <erikba@xxxxxxxxxxxxxxxxx> said:

> This --mtu-test option sounds extremely useful, unfortunately I haven't
> had a chance to try it out (versioning issues).
> 
> Is there any focus on speeding up mtu-test, so that it could theoretically
> be used to dynamically discover and use the best MTU in both directions,
> outside of a test/diag/install environment?

Right now I'm leaving it as a diag option because

(1) I want to gather more data from actual real-world usage to see if it
really works, i.e. produces a working tunnel when the mtu-test result is used
as the mssfix parameter.

(2) Making it run fast would be more complicated to implement because you
would need to manage congestion control.  Part of the inefficiency comes from
the fact that large packets need to be sent back and forth and they need to be
sent several times to make sure that lack of reception is due to an MTU
problem and not just a regular network hiccup.  There is definitely room for
improvement though -- such as using a binary rather than a linear search, and
making the mtu load-test protocol smarter.

(3) Since it only works between 2 recent versions of OpenVPN I think that it
would be more difficult to support right now, because a lot of people would
try to use a new openvpn with an old version and of course the old version
would not recognize the new mtu load-test packets.

James




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