DNS Settings (mlunix)

This is my first message on the forum so I’m software engineer.
I just started with Multitech Conduit mLunix I have succeeded to configured and set a Eth connection but My gateway can’t access to internet due to DNS settings.
I tried to set my DNS in resolv.conf file but always i had the following commands :

root@mtcdt:~# ping 8.8.8.8
PING 8.8.8.8 (8.8.8.8) 56(84) bytes of data.
64 bytes from 8.8.8.8: icmp_seq=1 ttl=57 time=29.7 ms
64 bytes from 8.8.8.8: icmp_seq=2 ttl=57 time=28.9 ms

Then

root@mtcdt:~# wget google.com
--2017-11-09 21:22:24--  http://google.com/
Resolving google.com... failed: Name or service not known.
wget: unable to resolve host address 'google.com'

I have noticed that after reboot I lose the DNS settings !!

What do you think ?

Thanks a lot for your help
Amine LTAIEF