15.3 Network Addresses
When you communicate across a computer network, you ultimately communicate with one particular computer out of all possible computers in the world. There is a fairly sophisticated mechanism for identifying specific machines to establish that communication.
A hostname is a unique identification that specifies a particular computer on the Internet. Hostnames are generally readable words separated by dots. For example:
matisse.csc.villanova.edu
condor.develocorp.com
We humans prefer to use hostnames when dealing with email addresses and websites because they are easy to use and remember. Behind the scenes, however, network software translates a hostname into its corresponding IP address, which is easier for a computer to use. An IP address can be represented as a series of four decimal numbers separated by dots. For example:
205.39.155.18
193.133.20.4
One form of IP address is stored in 32 bits and referred to as IP4. Each number in an IP address corresponds to one byte in the IP address. Because one byte (8 bits) can represent 256 things, each number in an IP address is in the range of 0 to 255. See FIGURE 15.10. The addressing scheme is hierarchical, with the first two numbers representing the network, the third representing the subnetwork, and the last representing the particular host machine.
FIGURE 15.10 An IP address stored in four bytes
A major problem with the IPv4 strategy is that it is limited in the number of unique computers (around four billion) it could identify. As Internet use increased, especially with the popularity of mobile computing devices such as smartphones and tablets, the supply of unique 4-byte IP addresses dwindled. In early 2011, the last block of IPv4 addresses was assigned.
IPv6 is the successor to IPv4. Instead of using 32 bits, organized in four groups of eight, IPv6 addresses use 128 bits, organized in eight groups of 16. An IPv6 address is usually written using hexadecimal digits to keep the length manageable. For example:
FE80:0000:0000:0000:0202:B3FF:FE1E:8329
In addition to providing many more addresses, the IPv6 protocol provides several additional features that improve the management of network traffic. IPv6 operates in parallel with IPv4 addressing, creating essentially two parallel networks.
Domain Name System
A hostname consists of the computer name followed by the domain name. For example, in the hostname
matisse.csc.villanova.edu
matisse is the name of a particular computer, and csc.villanova.edu is the domain name. A domain name is separated into two or more sections that specify the organization, and possibly a subset of an organization, of which the computer is a part. In this example, matisse is a computer in the Department of Computing Sciences at Villanova University.
The domain names narrow in on a particular set of networks controlled by a particular organization. Note that two organizations (or even suborganizations) can have a computer named the same thing because the domain name makes it clear which one is being referred to.
The very last section of the domain is called its top-level domain (TLD) name. FIGURE 15.11 lists some of the primary top-level domains. Some TLDs (noted by asterisks in Figure 15.11) have been around since the Internet was first established; others are relatively recent additions.
FIGURE 15.11 Some top-level domains and their general purpose (* indicates an original TLD)
ICANN, which stands for Internet Corporation for Assigned Names and Numbers, is the international authority that manages TLD names.
A TLD generally indicates a particular type of organization, such as .com for commercial businesses and .edu for colleges and universities. Some TLDs (such as .edu) are carefully controlled, with registration restricted to only bona fide organizations of a particular type. Other TLDs are unrestricted in that sense. Organizations based in countries other than the United States often use a top-level domain that corresponds to their two-letter country codes. Some of these codes (there are hundgreen1s of them) are listed in FIGURE 15.12.
FIGURE 15.12 Some of the top-level domain names based on country codes
The unrestricted nature of the .com, .org, and .net TLDs initially allowed anyone or any organization to register a domain name for its own use as long as that name hadn’t already been taken. As the Internet expanded, this naming system became a problem. Newcomers to the Internet lamented that the best domain names had already been taken. Sometimes a name had already been claimed by another similar organization. In other cases people tried to claim as many popular names as possible, hoping to sell (some would say ransom) them to large corporations.
This practice is called domain squatting, and is generally considered unethical. To alleviate this problem, additional top-level domains have been approved and made available over time. The ability to register a domain name using one of the newer TLDs has been somewhat controlled, giving preference to organizations that hold trademarks on particular names.
In 2011, the pressure for more domain options led ICANN to approve a program to greatly expand the number of generic TLDs. Companies and organizations were allowed to submit applications for potential new TLDs.
Some of the TLDs are controlled by particular corporate brands, but others are available for general use. There are now more than 1,500 TLDs available.
Here is a very small, random selection of TLDs that are available:
A full list of the names and their availability can be found at:
www.iana.org/domains/root/db. IANA is a department of ICANN.
The domain name system (DNS) is chiefly used to translate hostnames into numeric IP addresses. Before the DNS system was established, a Stanford research group maintained a single file known as the host table. As new hostnames were established, the Stanford group would add them to the table (usually twice a week). System administrators would retrieve the revised host table occasionally to update their domain name servers, which are computers that translate (resolve) a hostname into its IP address.
As the number of hostnames grew, the single-table approach became unreasonable. It simply wasn’t a practical way to update and distribute the information. In 1984, network engineers designed the more sophisticated domain name system that is in use today. DNS is an example of a distributed database; no one organization is responsible for updating the hostname/IP mappings.
When you specify a hostname in a browser window or email address, the browser or email software sends a request to a nearby domain name server. If that server can resolve the hostname, it does so. If not, that server asks another domain name server for help. If the second server can’t resolve it, the request continues to propagate. Ultimately, either the request reaches a server that can resolve the name or the request expires because it took too much time to resolve.
Who Controls the Internet?
These are interesting times for the Internet. Two recent developments, in particular, may have significant impacts on its use.
The Internet began as the ARPANET, a project of the U.S. Department of Defense. Initially, the United States explicitly controlled the assignment and management of IP addresses and domain names. In 1998, those responsibilities were subcontracted to ICANN, an international nonprofit organization, but the United States remained the dominant player.
In March 2014, the U.S. government announced that it will reduce its role in this process. It was widely expected that the United States would eventually decrease its role, but that effort was spurred forward by revelations that U.S. intelligence agencies such as the NSA have been intercepting Internet traffic.
As you can imagine, there is great concern across the globe about how exactly this new governing organization will work. Many voices from around the world will vie to be heard as these important decisions are made.
Another Internet-related issue comes from a recent plan suggested by the Federal Communications Commission (FCC) to allow ISPs to provide “premium” access to certain customers. Currently, no distinction is made between customers. Information is transmitted to everyone as fast as the technology allows. The new plan would allow ISPs to transfer data at higher speeds to those who pay for the privilege, perhaps by deliberately slowing down data transfer to those who don’t.
At the heart of this argument is the concept of network neutrality, which prohibits playing favorites among Internet consumers. This topic has become highly politicized, and how it plays out will have a significant impact on the use of the Internet.