I did a new install of DNN 6.01.01 into a new folder under C:\inetpub on IIS 7.0. I added a new Application to the Default Web Site and set the physical path to the new folder. After running INSTALL successfully, I could access the DNN Default Web Site (the host portal). I assigned 2 portal aliases to the host portal: localhost/appname and servername/appname. 

I then created 4 new, parent portals for the 4 domains hosted on this server. For each portal, I created 2 portal aliases: localhost/domain and servername/domain. 

I can access the host portal both locally (on the server in IIS) and remotely, using http://servername/appname. I cannot access the other parent portals using either of their portal aliases. Both links return error 404.0 (not found).

Can anyone suggest what I've done wrong here?

Thank you.

No. My understanding is that DNN doesn't not use host headers.

DotNetNuke does not use host headers, it simply reads the URL of the request that makes it to it. However to make it to DotNetNuke, IIS needs to know what URL's are expected so it can rout them correctly (the combination of IP address, port number and host header is what uniquely identifies a request to a website in IIS).

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