Virtual Hosting

Virtual hosting is the concurrent operation ( hosting) multiple domains or IP addresses on a server or host. There are two basic variants of the Virtual Hosting Virtualization Internet-based services. They differ in the method of the server applies when a request to determine which of the services it is providing was raised.

IP-based virtual hosting

A host can have multiple network interfaces. On each network interface of a host can be configured multiple IP addresses ( alias interface ). The applications running on the host server or virtual server can bind to one or more of these IP addresses. That is, different servers at different IP addresses are accessible to the host. From the perspective of the client, the servers are independent of each other. This method is more robust than the name-based virtual hosting discussed below.

Name-based virtual hosting

Many servers offer the opportunity to offer their services at the same time for different domains, regardless of whether the server is bound to one or more IP addresses. The distinction, for which domain the service has been requested shall be taken at the application level. Thus, for example, a mail server at the SMTP handshake recognize the desired domain of the recipient. In HTTP, the distinction based on the HTTP header field Host is made.

This process is called name -based virtual hosting or as a Virtual Domain. The latter term is misleading, because the domain is not virtualized, but the current under whose name services.

Pure name -based virtual hosting is usually used for virtual servers, as several non-virtual servers can not answer on a common IP address connections and thus a distinction is no advantage by name.

This method is less robust than the IP-based virtual hosting. In the HTTP protocol, for example, is the client side assuming HTTP/1.1 what eludes the influence of the server operator in the rule. For HTTPS connections is also necessary to support Server Name Indication on the server and the client side for a suitable allocation of allowances to the domains.

Advantage of the name-based virtual hosting is the server-side lower maintenance costs and lower consumption of IP addresses, which, in particular, is an important argument for large servers that host services for several hundreds or even thousands of domains.

  • Virtualization
  • System Administration
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