root@----:/# mount -t cifs //SERVER/smbtest /mnt/smbtest --verbose -o ver=2.1,user=administrator
Password:
mount.cifs kernel mount options:
ip=10.16.0.40,unc=\server.domain.netsmbtest,ver=2.1,ver=1,user=administrator,pass=********
mount error(22): Invalid argument
Refer to the mount.cifs(8) manual page (e.g. man mount.cifs)

"The minimum version for use of the Linux kernel SMB3 support is kernel version 3.12 (or backport of cifs.ko module version 2.02 or later) but kernel version 3.18 or later (or equivalent, ie cifs module version 2.04 or later) is recommended for best SMB3 support."

vers=
       SMB protocol version. Allowed values are:

       ·   1.0 - The classic CIFS/SMBv1 protocol. This is the default.

       ·   2.0 - The SMBv2.002 protocol. This was initially introduced in
           Windows Vista Service Pack 1, and Windows Server 2008. Note
           that the initial release version of Windows Vista spoke a
           slightly different dialect (2.000) that is not supported....

mount -t cifs //192.168.1.1/public /home/user/Desktop/share --verbose -o vers=2.1,user=winuser