Whats the difference between host headers and alternate access mappings?

This is a similar question - What are the differences between extending a web app and adding a host header then adding alternate access mappings in SharePoint 2010 but I'm afraid I don't really follow the English in the question.

  • So, what is it that you cannot follow? A specific term?
    – AlexPoint
    Commented Jun 8, 2011 at 8:44
  • @AlexPoint, you mean with regards to the linked question?? I'm guessing English is not the original questioners first language... so its not quite clear (to me) what is being asked/answered.
    – gotsp
    Commented Jun 8, 2011 at 23:52

1 Answer 1


When you extend a SharePoint web application, you are telling SharePoint to go to IIS and create a new site, but SharePoint will use it to show the same content. You would normally do that to support different security, authentication and URLs between an Internet site, Intranet and Extranet, for example.

When you add a host header it is equivalent to going to IIS and modifying the HTTP bindings for a site, and adding another URL or port. Generally, for simplicity, it is best to let SharePoint manage IIS and not go changing things in IIS Manager if you can avoid it. Host Header site collections are a mechanism to allow you to map different host headers to individual site collections within the same SharePoint web application.

The purpose of alternate access mappings is to deal with the situation where you have a load balancer or a proxy server that translates from an external URL to your server's internal URL. This ensures that the relative URLs generated by SharePoint when rendering pages are consistent with the external URL. Configuring alternate access mappings does not automatically add host header entries.

  • Thanks for the explaination. I'm finding myself in this situation with a couple things we're doing. We spin up new web apps so infrequently the process can get fuzzy quickly, especially when vanity host headers are wanting to be used. Commented Jun 8, 2011 at 12:44
  • SPDoctor, your answer is one of the best I've read! thanks
    – user7780
    Commented Apr 9, 2012 at 16:59

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