Virtual web hosting

Virtual web hosting is the process of running a number of "virtual" web servers on a single physical host computer. This enables a single computer to host thousands of independent web sites. Commercial virtual web hosting service providers often use this technique to be able to manage their hosting infrastructure well also for efficient and scalable hosting service. Most virtual web hosting applications rely on virtual DNS resolution, so that a specific domain name (such as a customer's own registered domain name) may be associated with each independent virtual web hosting server. This can be achieved through either name-based or IP-based virtual web hosting. These techniques are explained below. Name-based virtual web hosting is one technique implemented when providing virtual web hosting services. In this virtual web hosting method, each website hosted on a single machine shares a single public IP address. All HTTP GET command received by this web server are answered according to the domain name supplied by the requesting client, enabling the web server to differentiate between multiple virtual sites on the one IP address.

Another technique used when providing virtual web hosting services is the IP-based hosting. In this virtual web hosting method, each web site hosted on a single machine is given its own separate public IP address. The HTTP GET requests are answered by using IP address instead of the name. The limitations in operating system also limit the maximum number of IP addresses that can be assigned to a single machine particularly if separate log files are used. The Host request-header field is the field that specifies the internet host and port number of the resource requested as obtained from the original URL given by the user or referring source. It is necessary for the host field to represent the naming authority of the origin server or gateway given by the original URL. This will allow the gateway or origin server to tell the difference between internally ambiguous URLs. Name-based virtual web hosting is usually used by web sites that do not require special security requirements. For instance, name-based virtual web hosting is suitable for personal web sites or servers that can be accessible using more than one domain name.

Name-based virtual web hosting has few technical limitations. One limitation is that some websites require you to use SSL (Secure Sockets Layer) for e-commerce services. This is especially true in cases where a separate certificate is used for each virtual domain and also in anonymous log-in functionality with FTP services. Browsers that are only HTTP/1.0 compliant can view websites that are hosted by name-based virtual web hosting system if the version of the browser issues requests with an additional Host: header field.

Browsers who are not HTTP1.0 compliant could not use that as a justification to be allowed large scale IP-based hosting. Statistics collected by APNIC showed that in a four month period, browsers visiting www.apnic.net has the Host:header filed in 98.9% of HTTP1.0 and 99.8% of HTTP1.1 cases. APNIC thereby strongly recommend the name-based virtual web hosting system. Those that do not provide name-based virtual web hosting must be able to provide technical reason for this.
If you assign more than /22 for IP-based virtual web hosting, you will be required to list each IP addresses assigned for web hosting and their URLs in your succeeding request for an address space from APNIC. Name-based web hosting is strongly encouraged during the APRICOT 2000 in Seoul, Korea.