OpenVPN Config file – How to understand it

Each VPN provider will provide you with a config file.  If you open this config using Notepad, then it will read something like this.

VPNBook- UDP Port 53 Client config file

- Client (You’re the client, not the server, so we’re off to a good start).
- Protocol = UDP  (UDP is faster than TCP, so this is the fastest form of VPN).
- Remote = VPNBook server – the port we connect on is Port 53

-Resolve & retry = infinite = keep trying

-MTU = maximum transmission unit.  Consider packets stacked like suitcases in an airplane.  Each suitcase has a maximum weight and size.  This MTU confirms the maximum weight of each suitcase allowed – to fly with British Airways OpenVPN.

-Persist = keep trying
-CA = Certificate authority.  The .CRT file is their certificate.
-auth-user-pass = look for a password file (called password.txt)
-verb = verbose level.  How “chatty” the error messages are.
- cipher = AES 256

So when you download the UDP Port 53 config file from VPNBook, that’s what the file is saying to your computer.
*****

Line 1 – We are the “client”.

• Client

• device = tun.  Each VPN tunnel has 4 Devices.  2 are real IP, and the other 2 are virtual IP numbers.  If it’s not tun, it will read dev tap.

Step 2 – Remote means the OpenVPN server

• Protocol = is UDP.

• If not UDP, the protocol would be TCP.

• remote (the server) and the IP/Port that we need to connect on

• A setting to retry the connection (very handy if the connection fails, or we’re on a busy network)

Line 3 – Persist and HTTP proxy settings (if they’re being used)

• Persist

• Http Proxy

Line 4 -  SSL

• SSL is the security for your Browser (Firefox or IE).

• It checks the certificate (that’s a .crt file)

• And uses a key for each client (that’s the .key file)

Line 5 – Verify the certificate and SSL security

• TLS is the newer version of SSL.

• So this TLS-auth is about the browser security or SSL secret keys.

• It’s also handy for stopping DOS attacks

Line 6 – 007 James Bond Spy keys go here

• Cipher – server/client must agree on an encryption system – to encrypt your data.

• AES 256 is very strong, unbreakable in fact.

• comp-lzo = Allow compression.

Hopefully, when you get error messages now, you’ll understand what has gone wrong.
Eg if the error says TLS keys – that means the SSL key exchange has not happened in the time allowed – this would close the session.  The keys are needed to encrypt your message.  If it fails, OpenVPN won’t allow you to connect, as it’s unsafe.

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