I have DNN installed in my root domain (e.g., mainsite.com).  I want to create a parent portal "xyz" off the root DNN install that can be accessed using the url "xyz.mainsite.com".  My understanding is that I can accomplish this by doing the following:

1) create a parent portal and in the portal alias put in "xyz.mainsite.com"
2) add an "A" record to the DNS with name "xyz.mainsite.com" pointing to the IP address (same IP as "mainsite.com")

Is that all I need to do?  Or:
-- Do I need to create a subdomain called "xyz" (which creates the DNS record automatically) instead of doing #2 above?  If so, do I choose "Physical hosting" or "Subdomain on subfolder" as the hosting type?
-- Do I need to ask 3Essentials to put "xyz.mainsite.com" into the host header of IIS?

Sorry for the basic questions, but I've gotten different instructions/information from 3Essentials support depending on who's responding.

Thank you - that is what I suspected.  I've done all 3 of those steps, but they also said I had to create a subdomain which I did.  I'm wondering if I delete the subdomain now if that will adversely affect things?  Or should I leave well enough alone since everything is working?