If you leave the IP address for your new site as All Unassigned,
your new site will be the default web site for your computer,
which is the web site the server returns when a browser tries to
access an IP address not currently assigned to another site. For
example, if a computer has three IP addresses--172.16.12.50,
172.16.12.51, and 172.16.12.52--and only the first address has
been assigned to a site, then opening the URLs
http://172.16.12.52 will return the default web site. It's a
good idea to have a default web site configured with general
contact information about your company on a server that will be
hosting many sites. Note that if there is already a web site
that has All Unassigned for its IP address (such as the Default
Web Site created when IIS is installed) then if you assign All
Unassigned to another site you won't be able to start that site.
Host headers are a feature of the HTTP/1.1 specification and
allow IIS to host multiple web sites that have the same IP
address and port number but different