[Samba] Share mounts in SMBv1 mode, but fails weirdly in SMBv2 mode

[Hadrien Grasland]

Hi,

We're slowly deprecating SMBv1 support at work, so I'm trying to mount 
our Samba network shares using SMBv2.0. This should in principle be 
supported by the server, and seems works well enough for the Windows 
clients. But it fails for me with some errors which I do not understand.

Can you help me figure out what's going on? Here's my system 
configuration and a quick summary of what I have so far:

hadrien at linux-2ak3:~> uname -a
Linux linux-2ak3 4.13.5-1-default #1 SMP PREEMPT Thu Oct 5 18:28:26 UTC 
2017 (3fd9659) x86_64 x86_64 x86_64 GNU/Linux
hadrien at linux-2ak3:~> /sbin/mount.cifs --version
mount.cifs version: 6.5
hadrien at linux-2ak3:~> sudo mount -v -t cifs //nfsserv22/expsi test -o 
credentials=<path to credentials file>,vers=2.0
domain=LAL
mount.cifs kernel mount options: 
ip=134.158.91.155,unc=\\nfsserv22\expsi,vers=2.0,user=grasland,,domain=LAL,pass=********
mount error(95): Operation not supported
Refer to the mount.cifs(8) manual page (e.g. man mount.cifs)
hadrien at linux-2ak3:~> dmesg | tail
[...]
[13424.783242] CIFS VFS: ioctl error in smb2_get_dfs_refer rc=-2
[13424.789504] CIFS VFS: cifs_read_super: get root inode failed

Replacing "vers=2.0" with "vers=1.0" in the mount command line makes 
this work, so I'm quite confident that my general configuration is 
correct and the problem is somehow specific to the SMBv2 protocol. 
However, I'm a Samba newbie and would welcome any tips on how to extract 
more information from this machine/server in order to figure out why 
SMBv2 specifically is failing.

Thanks in advance for your help,
Hadrien Grasland