Domain Names and IP Addresses
Every host computer – server or otherwise – on the Internet is assigned an IP address. IP addresses are four-part, all-numeric “handles” that are easily used by networks. For instance, the Community Information site for East Lansing, Michigan has a host name of www.ci.east-lansing.mi.us; it has a corresponding IP address of 205.153.190.140.
In general, each computer on the Internet has its own host name and its own IP address. However, it’s possible for a single computer to have more than one host name. For instance, you may want to register both ci.smallville.mi.us and www.ci.smallville.mi.us as host names for your Web server. This allows users who guess your host name to find the computer either way. In this case, your server administrator simply creates an “alias” in your DNS tables so that both host names correspond to the same IP address.
In this example, the Web server for the Jet Propulsion Laboratory, jpl.nasa.gov, has been assigned the IP address 137.78.160.21. Normally the only people who have to worry about IP addresses are the administrators of servers or networks. If an organization handles its own IP address administration, it will be assigned a pool of IP addresses to use when new computers are installed. If IP administration is handled by an organization’s ISP, new addresses will be assigned by the ISP’s domain administrator, and given to the administrator of each new server as it is installed.
It’s also possible for a single physical computer to have more than one IP address associated with it. This may be done to support virtual hosts, or it may be done if the server has more than one LAN (Ethernet) adapter installed for performance reasons. In the most common case, you will only have one IP address per server (or other computer) you install.
Generally speaking, you never want to publish the IP address of your Web server – or any other server. Let the DNS map the friendly host names to IP addresses for you and your users. Users should see friendly, domain-style host names, not IP addresses, in the URLs your publish and in the “Location” box on their Web browsers.
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