You can set specifics DNS servers in Ubuntu.

Runtime DNS

vim /etc/resolv.conf

Add some nameserver entries:

nameserver 172.16.100.1
nameserver fd00::3631:c4ff:fefd:6ca8
nameserver 208.67.222.222

Permanent changes

vim /etc/resolvconf/resolv.conf.d/base

Add the DNS you'd like to use:

# OpenDNS servers
nameserver 208.67.222.222
nameserver 208.67.220.220
nameserver 2620:0:ccc::2
nameserver 2620:0:ccd::2

To apply changes immediately:

resolvconf -u

or just reboot to ensure it works!