Sharepoint zone authentication doesn't work

Question

I have a Sharepoint 2010 web application using claims based authentication. It contains three zones (two extensions). The first, main zone works fine. The second (intranet) asks for the credentials but doesn't authenticate. The third (extranet, anonymous) doesn't work at all. Every zone uses the same port which is 80. We use our custom domain controller. Main application has the following address computerName.domain. Intranet and extranet extensions have addresses like prefix.computerName.domain. It's unfortunately a legacy code so we're totally blind, moreover we're Sharepoint beginners. Interesting phenomenon is the second zone (intranet), when installed on different port, works almost fine, anyway authenticates properly.

Could anyone give me any advice about the situation? What can be the reason of the lack of authentication in the intranet zone? Why the third, anonymous extension doesn't work at all?

Answer 1

Here's the solution for the authentication issue:

http://support.microsoft.com/kb/896861

(Add DWORD value 1 named DisableLoopbackCheck to the registry key HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Lsa and reboot)

I used the first method described in the document. It works for the intranet zone.