Prior to the version 6.0 release of Sun Java System Web Server, there were two kinds of virtual servers: hardware and software. Hardware virtual servers had unique IP addresses associated with them. Software virtual servers did not have unique IP addresses, but instead had unique URL hosts.
In Sun Java System Web Server 6.0 and Sun Java System Web Server 6.1, these concepts are no longer quite accurate. All virtual servers have a URL host specified. However, the virtual server may also be associated with an IP address based on its listen socket.
When a new request comes in, the server determines which virtual server to send it to based on the IP address or the value in the Host header. It evaluates the IP address first. For more information, see Virtual Server Selection for Request Processing.