To avoid many questions and simplify troubleshooting, I would suggest this order when configuring AAM, which worked for me so far :
- Understand what AAM is, and what is it being used for in your particular case. (Read the blog posts below).
- Create a top level site collection in the application that you are trying to configure ( like http://mymossserver )
- Browse the site, make sure it works
- Complete the network configuration for the alternate URL that you are planning to use ( like http://intranet.mycompany.com ). If you do not know how to do this part, get your network administrator involved. This is a fundamental requirement to get it working.
- Create the host header entries on IIS for the web application you are trying to configure. If you do not know how to do this, get your IIS admin, or system admin (whomever configures IIS in your environment) involved. This is a fundamental requirement to get it working.
- Then browse the site using the new url you have configured. If you have configured it correctly, you should be able to browse the sharepoint site with the configured URL ( http://intranet.mycompany.com ), but redirected to the default zone mapping you have at this point ( http://mymossserver )... This means the network is capable of transporting the request to IIS, and IIS is capable of handing the request to the correct SharePoint web application.
- Then add the AAM for the desired zone in central admin, and make sure you have ONE mapping configured for each zone. (intranet zone in this case) Beware, the default zone will be selected when you open the page, you probably want to CHANGE IT...
- Browse the site with the new URL (http://intranet.mycompany.com). Voila ! Note: If you added two mappings to the same zone, you will see the exact same symptom of getting redirected to the first URL mapping in that zone...
Also remember; the zone and the URL mapping should be ONE-TO-ONE, not ONE-TO-MANY, and not MANY-TO-ONE. There is nothing in the UI to prevent you from entering the same url for different zones, or add two URLs to the same zone, so you can add it, but it either won't work as expected at all, or it will be partially broken. In total, you have 5 total AAM available, one for each zone.