[Samba] "mount error(112): Host is down" on Ubuntu 17.10

[Gao]

Hello,

I am a long time Samba user but new to this list. Now I need some help 
on a CIFS mount issue I just encountered.

We have 4 Samba servers:
ServerA: Samba 3.0.28a
ServerB: Samba 3.6.25
ServerC: Samba 4.3.11
ServerD: Samba 4.3.11

I am using a BASH script to mount shares in user's home directory using 
this line:
sudo mount.cifs //192.168.123.29/share/ ~/server/share -o 
user=<user>,password=<password>,uid=<uid>,rw,mand,mapchars

Everything works fine with Ubuntu LTS v12.04, v14.04 and v16.04.

Now Ubuntu released v17.10 and it has many changes so I want to test it 
out. Now I found my script no logger working on ServerA and ServerB. For 
Server C and D it works fine.

So I manually execute the mount.cifs command in terminal and it give me 
error:
$ sudo mount.cifs --verbose //192.168.123.29/staff/ ~/kappa/staff -o 
user=gao,password=mypassword,uid=1012,rw,mand,mapchars
mount.cifs kernel mount options: 
ip=192.168.123.29,unc=\\192.168.123.29\staff,mapchars,uid=1012,user=gao,pass=********
mount error(112): Host is down
Refer to the mount.cifs(8) manual page (e.g. man mount.cifs)

It seems lot people have this "Host down" error from the results of 
googling. I tried to add "-o vers=2.0" but it still not working:
$ sudo mount.cifs --verbose //192.168.123.29/staff/ ~/kappa/staff -o 
user=gao,password=mypassword,uid=1012,rw,mand,mapchars,vers=2.0
mount.cifs kernel mount options: 
ip=192.168.123.29,unc=\\192.168.123.29\staff,mapchars,vers=2.0,uid=1012,user=gao,pass=********
mount error(112): Host is down
Refer to the mount.cifs(8) manual page (e.g. man mount.cifs)

Also tried "vers=3.0" and no luck. Please help me. Thanks in advances.

Gao