Web Hosting and IP Addresses
IP address allocation for web hosting isn’t really a new topic, it has in fact been pretty well resolved for over a decade. But it’s still a point of confusion to some people, so here we go.
Websites have a hostname, like www.iphouse.com. When you click on a link or enter a URL into your web browser, the browser extracts the hostname from the URL and opens a connection to it. But the network doesn’t work with a hostname, it works with numeric IP addresses like 3522190849, which is usually written 18.104.22.168. So the web browser first has to look up the IP address for the hostname through DNS, the Domain Name System. Once it has an IP address, it can open a connection to the server and request the file.
There are two types of web hosting, named and numbered. With a named virtual host, many hostnames point at a single IP address for the server. When a web browser makes a request, it tells the web server the hostname which is being accessed and the server uses that to look in the correct place for the requested file. This is all part of the HTTP/1.1 standard, released back in 1997, and which every modern web server and web browser supports. Named virtual hosting is a very efficient use of IP addresses, which are otherwise a limited commodity, and the organization which oversees IP address allocation requires its use.
With a numbered virtual host, the IP address is associated with a single hostname. The only case which now justifies this is a web site which uses SSL encryption, since SSL is handled before the HTTP transaction and the web server has to respond with the correct SSL certificate before it knows the hostname. Thus, there can be only one hostname associated with the IP address.
There is an extension to SSL called Server Name Indication, which would provide hostname information earlier in the connection and allow named SSL hosting, but it is not currently in wide use.