If your DHCP server does not include nameservers, or if you need to use custom nameservers that are different than your DHCP server's leases, you can configure an alternate DNS manually.
As a site admin, SSH into your GitHub Enterprise instance:
ssh -p 122 admin@hostname
To edit your nameservers, enter
sudo vim /etc/resolvconf/resolv.conf.d/head.
nameserverentries, then save the file.
After verifying your changes, save the file.
To have GitHub Enterprise incorporate the new additions, enter
sudo service resolvconf restart.