handsomepete's Journal: Question for the Windows/IIS Know-somethings

Ok, I've been banging my head against a wall for a day or so trying to understand why this happens. Hopefully it's something stupid and simple and I can go on with my life. Forgive me if I refer to something incorrectly, I'll try to make sense and not embarrass myself.

Scenario:
Domain: MYDOMAIN (mydomain.com) (2003 Active Dir. in 2000 compat mode)
servera - 172.18.2.10 - Windows 2000 server, IIS 5
websitea - 172.18.100.30 - DNS A record for intranet website on servera

IIS configuration of websitea on servera:
Integrated authentication, no anonymous. Local directory for .asp files. Using 172.18.100.30 as its only IP, the IP is assigned to the nic. It is _not_ the default site. Everything else (more or less) default.

When I go to http://websitea/ from any box in the domain my NT credentials pass through to IIS and work fine without prompting for a username/password whether it's a new session or not. That's what I think should happen. When I go to http://websitea.mydomain.com/, I get asked for a username/password (with servera.mydomain.com in the title bar of the password dialog box) every time I initially access the site.

Why?