What every SharePoint administrator needs to know about Alternate Access Mappings (Part 1 of 3)

SharePoint is compatible with a variety of reverse proxy servers, but for this example we'll take a look at a publishing rule from Microsoft's reverse proxy software - Internet Security and Acceleration Server 2006. ISA Server 2006 includes a SharePoint publishing wizard that walks you through creating a publishing rule for SharePoint. Once the rule is created, you can modify it at any time. (The following images show a slightly modified publishing rule where the "Forward the original host header" option is turned off to help demonstrate the flexibility of AAM. If we left the "Forward the original host header" option turned on, the public hostname would also serve as the internal hostname when configuring AAM.) The first two dialogs show the "listener" and "public name" properties of the rule, which define what URL users will use to access your SharePoint site. Remember that this URL is really the URL of your reverse proxy server, which will forward the request to your SharePoint server.

http://blogs.msdn.com/sharepoint/archive/2007/03/06/what-every-sharepoint-administrator-needs-to-know-about-alternate-access-mappings-part-1.aspx#9163002