Our internal AD is mycompany.local
Our internal sharepoint (and public) sharepoint site is portal.mycompany.com
We use NTLM authentication and it works fine. We don't need to put domain\user.
We created a sharepoint site for myothercompany.com - sharepoint.myothercomany.com
We are hoping to use the same internal AD for authentication.
If you're out on the internet - this site works and accepts the default domain. (mycompany.com)
However, if you're attached to us locally (via VPN) - the login pops up with sharepoint.myothercompany.com\user instead of just accepting the mycompany\user. I have to manually type mycompany\user in order for it to work. The two IIS sites look identical - yet one application forces domain\user.
IIS is set with the default domain as mycompany for both sites.