URL & IP Addresses


It is amazing to think that your computer can distinguish and access a file on a specific computer among over ten million computers connected to the Internet. URLs and IP addresses make it possible. Understanding URL and IP addresses is essential knowledge for understanding how the Internet works. What they are, how they work, and issues about IP addresses shortages are discussed in this paper.


Suppose you want to make a phone call to your friend. You can call her if you know her telephone number. If you do not know her number, you can look for her number by her name with a telephone book. In the Internet network, the telephone number corresponds to an IP address and her name corresponds to a domain name.  The telephone book is similar to the DNS.

IP Address (Internet Protocol Address)

·          An identifier for a computer or device on a TCP/IP network.

·          Used to distinguish one computer from other computers connected to a TCP/IP network such as Internet or Intranet

·          Assigned by ICANN (Internet Corporation for Assigned Names and Numbers) to every computer connected to an IP network and strictly controlled to avoid duplicates

·          Represented as a group of four numbers from 0 to 255 separated by periods (e.g. “123. 45. 225. 1.”) The format is based on IPv4 (Internet Protocol version 4)

·          Organized into hierarchical classes as follows:

·           Class A – all are huge organizations and require the highest possible categorization (i.e. General Electric Company, IBM Corporation, AT&T, Hewlett Packard Company, Ford Motor Company, and the Defense Information Systems Agency). Supports 16 million hosts on each of 128 networks

·           Class B – supports 65,000 hosts on each of 16,000 networks

·           Class C – supports 254 hosts on each of 2 million networks

·           Class D – intended for multicast purposes

·           Class E – reserved for future use

·          Because IP addresses are represented by numbers and they are too complicated to remember for humans, the idea of naming sites resulted in Web URLs and e-mail addresses.

URL (Uniform Resource Locator)

·          Represents an address of a certain file on the TCP/IP network and leads a user to a file on any computer connected to the Internet anywhere in the world.

·          The format is standardized as <the method of protocol to be used://the domain name/the directory name/the file name>

·         An example: <http://www.gmu.edu/departments/telecomm/special.html>

·           http: protocol to be used to search for the other protocols such as ftp, telnet, gopher

·           www.gmu.edu the domain or host name, the name of the network or the computer you are trying to contact, should be unique in the world

·           departments/telecomm/ indicates there is a folder or a directory named department and subdirectory named telecomm on the web site’s computer disk, should be connected with a slash (/)

·           special.html – the file name in the directory, could end with such as html, htm, cgi, etc.

Domain Name

·          The name that identifies one or more IP addresses. (i.e. www.gmu.edu represents many IP addresses)

·          Used in URLs to identify particular Web pages.

·          Most domain names are assigned by the InterNIC (Internet Network Information Center)

·          Taking <www.gmu.edu> as an example, a domain name is composed of a server (host) name (www), individual name (gmu), group name (edu), and country name in other countries. They are divided with periods.

·          A domain name is hierarchically structured as top level domain, second level domain, and third level domain, from the right hand side.

·          There are six top level domains (TLDs) in the U.S.:

·           .gov – government agencies

·           .edu – educational institutions

·           .org – organizations (nonprofit)

·           .mil – military

·           .com – commercial business

·           .net – network organizations

·          Examples of new TLDs:

·           .biz – businesses and corporations

·           .name – individuals’ and personal websites

·          Countries other than the U.S. have country codes as TLDs. TLDs mentioned above become second level domain with country codes. Examples of country codes are:

·           .it – Italy

·           .is Iceland

·           .jp Japan

·          Third level domain or second level domain in the U.S. indicates the individual name of the web site.

·          Because computers communicate with each other using IP addresses, not domain names, every Web server requires a Domain Name System (DNS) server to translate domain names into IP addresses.

DNS (Domain Name System)

·          As described in the beginning example, the DNS functions as a telephone book in the Internet world.

·          DNS is the system to link domain names and IP addresses to each other

·          Domain Name System is managed by Domain Name Servers all over the Internet

·          DNS maps a domain name to an IP address.

·          DNS mapping works as follows:

·           When a URL is typed into the browser, the DNS server searches for a matching IP address. (The DNS server is set by the Internet Service Provider)

·           If the DNS server does not find an entry in its database, it will ask the Internet’s root server, which is the center of all DNS servers

·           The root server indicates the DNS server that has a database for the top level domain.

·           The DNS server for the top level domain finds the DNS server for second level domain

·           This process keeps going until the entry is found.

·          Accordingly, the procedure to access the website is follows:

·           A URL address is entered in the browser, such as Netscape Navigator or Internet Explorer.

·           DNS server translates a domain name into an IP address.

·           Access the computer of the website and ask the computer to forward the file.

·           The file is forwarded and the browser displays the file on the computer.


Are there enough IP addresses for all computers? As described above, IP addresses are represented as an aggregate of four numbers from 0 to 255, which means that IP addresses can be allocated up to 4,294,960,000 computers, which will be running out in the near future.

IPv6 (Internet Protocol version 6)

·          The new proposed Internet Protocol designed to replace and enhance the present IPv4 protocol.

·          IPV6’s 128-bits format can offer more than 340 duodecillion, or 34 trillion trillion trillion IP addresses.

·          IPv6 can be the reason for success of mobile communications because:

·           The next generation networks, 3G networks, will take great advantage of IPv6 since the wireless data network is expected to expand vastly and more and more wireless devices will need to be connected to the Internet.

·           It can assign an IP address not only to every wireless device but also to every device’s potential location. It simplifies the tracking and routing of calls.

·           It can be a global wireless standard since IPv6 offers interoperability with existing services, portability of services so users can move around, and device independent content so that users do no lose functionality.

·         Other advantages are:

·           More Internet efficiency by reducing the scale of the routing task

·           Faster packets transport by simplifying the protocol

·           More security

·         In spite of those advantages, the move for adoption of IPv6 has been slow because:

·           Expensive to upgrade

·           The wired industry is not in a rush too much to get more IP addresses comparing to the fact that the wireless industry needs them desperately

·           Lack of leading organizations desiring to move into IPv6

·           While the U.S. has a huge influence on the decision of the Internet issues, the U.S. is enthusiastic to enter on IPv6. The U.S. is not short of IP addresses at present because many companies who have acquired Private IP addresses are now selling Global IP addresses back to the authority. (Private IP addresses are the IP addresses which can be used only in a particular network. Global IP addresses are the general IP addresses which should be unique in the world)

However, the fact that IP addresses are running out cannot be avoided. It seems that the world is starting to finally adopt IPv6.

·         The government of Japan and Europe, which are the developed wireless technologies countries, announced early adoption of IPv6.

·         Sun Microsystems has publicly started to support IPv6

·         Microsoft announced to deliver an IPv6 patch to Windows 2000


The Internet is essential for business and daily life now. With the knowledge of URL and IP addresses, Internet users can deepen their understanding of how the Internet works and exploit the Internet greatly.

Related Links

Webopedia. This is a great online telecommunication dictionary.


ICANN Homepage.


Uwhois.com. This website is a functional source to look for available domain names worldwide.


InterNIC. Try this site if you are interested in purchasing a domain name


URL as UI. An interesting site describes how to obtain a good and impressive domain name.


IP Addresses, Host Names, and Domain Names. The stock answer database by Information Systems department at Massachusetts Institute of Technologies


Internet, the first step. This is an online lecture for Internet beginners in Japanese