Administering an ISP Installation

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Hosting Multiple Sites with One IP Address

Many customers will not only request access to the Internet, but will also want to host their own domain (for example, ) or subdomain on an existing server. To handle this type of situation, IIS 5.0 offers two models for site configuration:

  • Multiple IP addresses on one server

  • Multiple host headers on one server with one IP address

Previous versions of IIS allowed you to host multiple Web sites (virtual servers or domains) on a single computer running Windows NT Server 4.0. By assigning a different IP address to each site (all on one computer), you could reduce the number of computers required in an ISP installation.

With IIS 4.0, a new feature was introduced that allowed hosting multiple Web sites with a single IP address. Continued in IIS 5.0, this feature works well if you do not have a lot of IP addresses to spare, but want to host several Web sites on one computer anyway. Instead of assigning each site a unique IP address, you give it a unique host header name. This feature works best for smaller sites with less traffic than it does for sites on a computer with unique IP addresses for each site.

Host header names are the key to hosting multiple Web sites on one computer. However, as mentioned earlier, not all browsers support them. Because host headers are part of HTTP 1.1, browsers must comply with HTTP 1.1 in order to access sites that do not have unique IP addresses. Microsoft Internet Explorer 3.0, Netscape Navigator 2.0, and later versions of both browsers support host header names, but earlier versions of the two browsers do not. For information about allowing older browsers to access a site through host header names, see Supporting NonHTTP 1.1Compliant Browsers .

The following examples show how to use host headers. The first example shows unique IP addresses assigned to multiple Web sites on one computer. The second example shows one IP address on one computer hosting multiple Web sites, differentiated only by their unique host header names.

See the following: