In order to connect a domain to HubSpot, your domain's name server host must have the ability to point a CNAME record to HubSpot.
Additionally, fully hosting your site with HubSpot requires a name server host that can set up a 301 redirect from the non-www version of your domain to the www version. If your DNS provider does not provide a 301 redirect, please reach out to our Support team and they can help you with a solution.
HubSpot requires the use of a CNAME to take advantage of HubSpot's state-of-the-art speed and security measures. To be more specific, HubSpot is not rendered via a simple set of webservers with single IP addresses, and therefore no IP addresses can be provided. CNAME records provide the global performance necessary to render sites faster, as HubSpot is delivered via local servers nearest to the requesting browser's geographic location. More importantly, our delivery network also allows us to provide the necessary protection to keep sites safe and functional in the face of any threats should one present itself.
For instructions on connecting a domain and taking your content live with HubSpot, please refer to this article.