Our dns servers information is as follows:
dns.trouble-free.net (66.45.228.79)
dns2.trouble-free.net (66.45.228.4)
If you need a third nameserver use the following:
ops.trouble-free.net (66.45.228.10)
You will need to contact support to insure the third server is added to your dns zone file.
You may also refer the following video tutorial about DNS Management.