how to find the smb protocol version that cifs-utils supported

netapp admin will close the smbv1 protocol, i have a try to specify the version on linux server, for exmaple:
server version: Red Hat Enterprise Linux Server release 6.9 (Santiago)
cifs-utils version :cifs-utils-4.8.1-20.el6.x86_64
mount -t cifs //netapp_cifs001/es /folder/subfolder -o username=username,password=password,rw,uid=53240,gid=53240,dir_mode=0770,file_mode=0770,vers=2.1

remount the share folder, and this connection still in netapp smbv1 list.
the version 2.1 didn't actually work. why...