Administering an ISP Installation

One Computer, Multiple IP Addresses

IIS 3.0 offered this option as the sole way to publish multiple sites on the Internet. ISPs could direct customers to two or more separate IP addresses and have the addresses and the domain names registered with InterNIC. This option remains cost-effective for two reasons:

• ISPs can minimize their hardware costs.

• As a specific site grows, it can be migrated onto its own dedicated server without interrupting customer access.

Having multiple IP addresses enhances security of Web sites contained on the server. For example, in some cases an ISP might host customers personal Web pages on one IP address. The ISP might then set up a second IP address, with IIS 5.0 and the FTP protocol enabled in order to let customers post content to their Web pages. This particular configuration will frustrate any would-be intruder, who might try to access the Web site. This intruder might try to capture FTP user names and passwords in two ways: either by attacking an FTP port on the site, or by performing a network sniff of the site.

The following example shows two Web sites (reskit1.microsoft.com and reskit2.microsoft.com) hosted on one computer with two different IP addresses (reskit1.microsoft.com = 172.21.13.45 and reskit2.microsoft.com = 192.168.114.201). Although you can see the host header field in the HTTP log, it is the network IP address (not the host header field) that differentiates between the Web sites.

This type of configuration works well for large installations that contain hundreds of Web sites and attract lots of hits.

CLIENT REQUEST FOR reskit1.microsoft.com

IP: Destination Address = 172.21.13.45

HTTP: Request Method = GET
HTTP: Uniform Resource Identifier = /
HTTP: Protocol Version = HTTP/1.1
HTTP: Accept = image/gif, image/x-xbitmap, image/jpeg, image/pjpeg, application/vnd.
HTTP: Accept-Language = en-us
HTTP: Accept-Encoding = gzip, deflate
HTTP: User-Agent = Mozilla/4.0 (compatible; MSIE 5.0; Windows 2000)
HTTP: Host = reskit1.microsoft.com
HTTP: Connection = Keep-Alive

CLIENT REQUEST FOR reskit2.microsoft.com

IP: Destination Address = 192.168.114.201

HTTP: Request Method = GET
HTTP: Uniform Resource Identifier = /
HTTP: Protocol Version = HTTP/1.1
HTTP: Accept = image/gif, image/x-xbitmap, image/jpeg, image/pjpeg, application/vnd.
HTTP: Accept-Language = en-us
HTTP: Accept-Encoding = gzip, deflate
HTTP: User-Agent = Mozilla/4.0 (compatible; MSIE 5.0; Windows 2000)
HTTP: Host = reskit2.microsoft.com
HTTP: Connection = Keep-Alive