Host Multiple Sites from One IP Address
IIS allows you to assign any number of sites to a single IP address. Host headers can be used to acheive this. When IIS receives a request for a Web page, it looks at the information sent in by the browser. The HTTP header contains the actual domain name requested. IIS uses this to determine which site should answer the request. 
Step-by-step procedure about how to configure host header names :
1. Start the Internet Service Manager (Inetmgr.exe).
2. Right-click the Web site to be configured, and then click Properties.
3. On the Web Site tab, select the IP address that the site will use.
Note: if you only have one IP address on the server, select All Unassigned, and set the TCP Port that should be used (usually 80).
4. Click Advanced.
5. In the Multiple identities for this Web Site list, select the identity that you want to use.
6. Click Edit, and then add the desired host header name.
NOTE: If you want this site to respond to more than one host header name, use the Add button to add additional identities to this list. Specify a different host header name for each identity, but be sure to use the same IP address and port.
7. Apply these changes and start the Web site (if it is not already running).
8. Register the host header name with the appropriate name resolution system.
If the computer is on an intranet (a private LAN that uses Internet technology), register it with the intranet’s name resolution system, such as the Windows Internet Name Service (WINS).
If the computer is on the Internet, register the host header name with the Domain Name System (DNS), which is administered by InterNic.
9. After the host header name is registered with the name resolution system, test it from a browser by attempting to browse the host header name. The browser should open the expected Web site.
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