With a Bare Metal Server there are four typical options for name servers:
1. Use your domain name registrar name servers to manage your domain names
2. Use SoftLayer name servers to manage your domain names
3. Use a third party DNS service to manage your domain names
4. Run your own name servers on your server to manage your domain names
Numbers 1, 2, &3 will want use name servers of the third party (ex. ns1.softlayer.com and ns2.softlayer.com). Option number 4 will use your domain as the name server (ns1.yourdomain.com & ns2.yourdomain.com). Option number 4 requires you to run DNS services on your server and you must also register your domain as a name server with your registrar. This is usually free, but requires an additional step beyond the basic domain name registration process.
SoftLayer offers free DNS services that are fully managed through the customer portal. We highly recommend allowing SoftLayer to manage your DNS and to act as your name servers due to our redundant systems, ease of management, and ability to quickly troubleshoot DNS related issues.