A shared web hosting service

or virtual hosting service or derive host refers to a web hosting service where many websites reside on one web server connected to the Internet. Each site “sits” on its own partition, or section/place on the server, to keep it separate from other sites. This is generally the most economical option for hosting, as many people share the overall cost of server maintenance.

Implementation

Shared web hosting can be accomplished in two ways: name-based and IP-based, although some control panels allow a mix of name-based and IP-based on the one server.

IP-based

In IP-based virtual hosting, also called dedicated IP hosting, each virtual host has a different IP address. The web server is configured with multiple physical network interfaces, or virtual network interfaces on the same physical interface. The web server software uses the IP address the client connects to in order to determine which web site to show the user. The issue of IPv4 address exhaustion means that IP addresses are an increasingly scarce resource, so the primary justification for a site to use a dedicated IP is to be able to use its own SSL certificate rather than a shared certificate.

Name-based

In name-based virtual hosting, also called shared IP hosting, the virtual hosts serve multiple hostnames on a single machine with a single IP address. This is possible because when a web browser requests a resource from a web server using HTTP/1.1 it includes the requested hostname as part of the request. The server uses this information to determine which web site to show the user.

Disadvantages

Name-based virtual hosts have some disadvantages:

• They will not work with very old HTTP/1.0 browsers that do not send the hostname as part of requests. Since the “Host” header is mandatory in HTTP/1.1, which was issued in 1999 as RFC 2616, this is not a common issue.
• They do not properly support secure websites using HTTPS. All name-based virtual hosts using the same IP address must share the same digital certificate because the SSL/TLS handshake takes place before the hostname is sent to the server. Server Name Indication is a potential solution but it is not yet widely implemented.
• If the Domain Name System is malfunctioning, or DNS changes haven’t propagated to all ISPs’ resolvers, it is not possible to fall back to using the IP address to contact the system. Some web hosting companies may offer an alternative access method like http://192.0.2.0/~virtualhostname or http://virtualhostname.hostingsite.com/ to provide access in such cases.
• If file permissions have been improperly configured, then shared file systems might give other (compromised) users or processes system-wide access to these files.