about the difference with using localhost, IP, domainname

hi All,

I configured Single Sign-On using IIS7 to access my application.

When I access this URL, SSO works:

http://localhost/MyAPP

but SSO setting doesn't work,When I enter following URL
http://mydomain.com/MyAPP OR http://10.20.30.40/MyAPP
In these cases it simply prompts for the user credentials and once I enter those (i.e. the NT username and password for the user currently logged in to the system) it allows normal access, the way it was otherwise allowing with URL,http://localhost/MyAPP

Does anyone know how I should configure to have SSO setting worked for the three URLs?

Thanks,

Jun