The open dns addresses: 184.108.40.206, 220.127.116.11
If you want to make the open dns addresses to be more permanent, you may try this option, which requires you to open a terminal:
1. Edit /etc/resolv.conf:
sudo pluma /etc/resolv.conf
2. If any nameserver lines appear, write down the IP addresses for future reference.
3. Replace the nameserver lines with, or add, the following lines:
prepend domain-name-servers 18.104.22.168, 22.214.171.124
4. Save and exit.
5. Restart any Internet clients you are using.
I do not guarantee that the above will work. Problems with connecting with the repositories are varied and so are the solutions.