I installed an instance of dnn 5.2.2 in www.website.com/portal. I tried  to create a parent portal as subdomain sub1.website.com. I added sub1.website.com to www.website.com host header/domain pointer. I could view this new portal in my host account of www.website.com but when i typed in sub1.website.com to my web browser, i got an error.

what am i doing wrong

I've sorted out the problem, all though I don't really understand it. The documentation I've read isn't clear about sub-domains and locating DNN in sub folders off the root.

Using Sub-domain URLs located in a sub-folder off the domain route. e.g. sub1.mydomain.com/portal can be accessed only if the main DNN is located in a sub-folder like mydomain.com/portal and the user types in http://sub1.mydomain.com/portal.  This isn't what I was looking for, because the "/portal" part of the URL makes the it clumsy for the user.

I re-installed the main DNN into root e.g. mydomain.com and can set up portals using sub-domain like URLs e.g. sub1.mydomain.com.

It'll be interesting to see what happens when I start setting up portals with other domain names e.g. www.mywebsite.com using the "host" DNN installation on www.mydomain.com!