Level 27
What is OpenVPN-NL:
A hardened version of OpenVPN that includes as many of the security measures required to operate in a classified environment as possible.
read more about it here:

Open VPN vs OpenVPN-NL:

Among the notable differences between OpenVPN and OpenVPN-NL is the cryptographic library. Correct SSL functionality is essential for the protection that OpenVPN offers. OpenSSL is a large and complex library. mbed TLS is a compact and modular library, which is small enough for a fairly in-depth evaluation. Therefore, in the OpenVPN-NL package, we exchange OpenSSL for mbed TLS. This change does not change functionality; the two libraries (OpenSSL and mbed TLS) are mutually compatible.

Apart from these differences, many things are the same. The functionality is nearly identical. OpenVPN and OpenVPN-NL are mutually interoperable, in the sense that a client of the one can connect to a server of the other (given that a crypto suite is chosen which is available in both products). OpenVPN and OpenVPN-NL are mutually compatible, in the sense that configuration files can be freely exchanged (given that the options are available in both products). Both OpenVPN and OpenVPN-NL and underlying libraries are licensed under GPLv2.

OpenVPN-NL was built according to the guidelines set by the Dutch government's national communications security agency (NBV, also known as the NLNCSA). This includes both hardening patches and improvements in documentation to ease evaluation.

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