Vagrant: Force provisioning ssh to be external ssh (not Ruby's Net::SSH)

https://developer.hashicorp.com/vagrant/docs/v2.4.0/vagrantfile/ssh_settings says: > config.ssh.extra_args (array of strings) - This settings value is > passed directly into the ssh executable. This allows you to pass any > arbitrary commands to do things such as reverse tunneling down into > the SSH program. These options can either be single flags set as > strings such as "-6" for IPV6 or an array of arguments such as ["-L", > "8008:localhost:80"] for enabling a tunnel from host port 8008 to port > 80 on guest. Note: This option only affects the ssh command or > instances where the SSH executable is invoked **(non-interactive SSH > connections use the internal SSH communicator which is unaffected by > this setting).** For my vagrant box I cannot use Ruby's SSH client. Can I force Vagrant to use the SSH executable with the config.ssh.extra_args? https://developer.hashicorp.com/vagrant/docs/v2.2.19/other/environmental-variables suggests setting VAGRANT_PREFER_SYSTEM_BIN - but it is unclear to what (I tried true and 1 and exporting the variable - Vagrant 2.2.19 still used Net::SSH).