There are two ways in which you can host more than one site on a single machine. One way is to assign each server a different IPaddress. At Zeus, we refer to these as IP virtual servers.

All modern browsers send an HTTP Host: header line, that tells the server the full IP name of the site being requested. This makes it possible to have multiple virtual servers on the same IP address. Because all the virtual hosting is done by the software(without altering the addresses or routing tables), these are often referred to as software virtual servers.

Okay, I understand - but how many can I host on a singlemachine?

With the Zeus software there is absolutely no limit on the number of virtual servers it can handle. However, that doesn't mean you can host every web server in the world from a single machine!

With IP virtual servers, the limit is generally imposed by the operating system's TCP stack. Most TCP stacks degrade in performance after they have a few hundred IP based virtual servers. Though OS technology is improving, the limit you will reach will almost certainlybe an OS one.

With software virtual servers this limit is avoided - you can host thousands of servers. However, as each one has its own configuration, the more servers you have, the more memory you will require. You should be able to host several thousand virtual servers in this way.

At this point when you are trying to administer several thousand different sites each with their own configuration, administration issues can become complicated. This is where the Subserver module comes in. The Zeus Subserver module is designed to address the needs of ISPs who want to host tens of thousands of sites from a single machine by using a grouped configuration. Using SubServers you will be able to host millions of sites from a single machine. See theSubserver configuration documentation for more information.

Bandwidth and Data Throughput Limitations

Note that if you are running a million sites from a single machine you are likely to generate a large amount of traffic to your site. Naturally a million sites will generate more traffic then a thousand sites. The real limit on the number of sites you can host is likely to be set by the amount of web traffic those sites create.