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Re: [Openvpn-users] Overhead added to each packet by OpenVPN?


  • Subject: Re: [Openvpn-users] Overhead added to each packet by OpenVPN?
  • From: James Yonan <jim@xxxxxxxxx>
  • Date: Tue, 30 Nov 2004 06:59:12 -0700 (MST)

On Mon, 29 Nov 2004, Rutger T. wrote:

> Dear group,
> 
> I have a few questions regarding OpenVPN that I hope that you may help
> answer: 1) Is OpenVPN a transport layer protocol? (At least that's what
> I gathered from reading the FAQ....)

Yes.

> 2) OpenVPN supports VoIP (UDP)
> traffic right?

Yes.

> 3) Finally, and most importantly, how much overhead is
> added to each encrypted packet by OpenVPN? (i.e. How much additional per
> packet overhead is there for using OpenVPN?)

It varies depending on options.  With a TUN-style tunnel over UDP using 
the default TLS options, the per-packet overhead is:

41 bytes security layer overhead (includes packet tag (1), HMAC-SHA1
signature (20), initialization vector (16), sequence number (4))

28 bytes tunneling overhead (includes IP + UDP header)

Total: 69 bytes per packet

If your data stream is compressible, you can potentially gain back all of 
this overhead.

James

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