In Windows Server 2012 R2 with IIS 8.5, I have an FTP site working fine with anonymous access, as long as no host name is specified in the site's bindings. As soon as I enter a value for the host name, the client browser (tested in Chrome) displays the "Authentication Required" prompt, asking for a user name and password.
I need to bind a host name because this server will host multiple FTP sites, but this issue is effectively preventing the use of a host name binding. I can't think of how the host name would affect authentication. Not using SSL.
To test for permissions problems I granted "Everyone" access to the physical path, with no change in behavior.
One setting I have that might be relevant is under the site's FTP Authentication > Anonymous Authentication > Edit > Anonymous user identity, I have a domain account specified. Using "View Effective Access" in Windows shows that this account has sufficient permissions in the physical path, and of course like I said it works fine without the host name specified.
How can I have anonymous access to an FTP site in IIS while also binding a host name for that site?