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I read a question here about this topic but actually I am not super sure whether I understood it correctly. Unfortunately, because of my low reputation I can't comment there, so I decided to ask here directly.

I think I understood in general the difference between UDP and TCP. Running an VPN on which I transfer files would make me want to use TCP as I want the data to be correct and complete. However, I read this post here, https://security.stackexchange.com/a/27844/191246. From this I got the feeling that with VPN it is a bit like a box in a box. So the inner data transfer is performed with TCP all the time, no matter whether the outer box i.e. VPN is using UDP or TCP.

So that would mean unregarding the setup of the VPN, let it be UDP or TCP, I have the guarantee that my files are transfered correctly. Is this right?

I want to replace my FritzBox VPN by an OpenVPN running on a Raspi and I really want to understand what implications are caused by certain decisions.

Thanks a lot, for your comments.

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  • You might wish to read [Openvpn-users]UDP Tunnel and Reliability. The URL is sourceforge.net/p/openvpn/mailman/openvpn-users/… – ssdhddinfected Nov 13 '18 at 20:05
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    So again I take the message that it doesn't really matter whether I take UDP or TCP regarding file consistency or integrity. Since the decision is only on the level of how the virtual network is set up and not on the actual file transfer. – FordPrefect Nov 13 '18 at 21:29
  • I suggest that you confirm your understanding with either Gregory Sloop or Gert Doering. You need to first sign up to the mailing list. – ssdhddinfected Nov 14 '18 at 5:23
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I got the feeling that with VPN it is a bit like a box in a box.

Good analogy. The VPN provides a "virtual" network adapter that, as far as your computer is concerned, is just another link to the outside world.

So the inner data transfer is performed with TCP all the time

The inner data transfer is performed using whatever protocol the data transfer software uses: UDP, TCP, or something more exotic. That transfer travels over the virtual network just like it would travel over a physical network if the VPN didn't exist.

So that would mean [...] I have the guarantee that my files are transfered correctly. Is this right?

If your file-transfer software provides that guarantee over a physical network, then the same guarantee applies over a VPN.

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    So lets say I use my laptop at home in my network and read and write files on a file server via samba. When I do the same via VPN it doesn't matter whether I use UDP or TCP I will have the same integrity in file transfer as I would have being at home. – FordPrefect Nov 13 '18 at 19:26
  • @FordPrefect yes, that is correct: Samba transfers its packets over the underlying network and doesn't care whether it's an Ethernet LAN, a VPN, or an RFC 1149 link. – mlp Nov 14 '18 at 16:55
  • Ok, I think I got it. It's really confusing because one can easily confuse the system of the VPN with the one of the service. Maybe I will ask at the mailing list as suggested in the comments above. – FordPrefect Nov 14 '18 at 17:35

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