AFAIK OpenVPN officially has GCM mode support since v2.4, which is relatively recent (official release December 2016). I'm sure it was also present in 2.3.x -

AFAIK OpenVPN officially has GCM mode support since v2.4, which is relatively recent (official release December 2016). I'm sure it was also present in 2.3.x - at the very least I'm certain that 2.3.10 I have on one host supports TLS-DHE-RSA-WITH-AES-256-GCM-SHA384 - but it could be distro-specific backports or something like that. At least 2.3 changelogs don't mention anything about AEAD or GCM specifically, and GCM support is featured in https://github.com/OpenVPN/openvpn/blob/release/2.4/Changes.rst https://github.com/OpenVPN/openvpn/blob/release/2.4/Changes....