IP Addresses
and Domain Names
04
In this lesson, you will learn about IP addresses and Domain Names. We will use an Networking Simulation App to explore how the Domain Name System (DNS) is used to look up the IP addresses of domain names such as google.com.
Technical Terminology
host - An Internet host computer is a computer that's connected directly to the Internet: often a computer that provides certain services or resources
router - A router is a device that transmits data between two different networks
IP Address - An IP Address is a unique string of numbers separated by periods that identifies each computer using the Internet Protocol to communicate over a network
domain name - An Internet domain name is a hierarchical name (such as trincoll.edu) that identifies a domain and an institution on the Internet. Top level domains include com, edu, gov
IPv4: IP version 4 is an older 32 bit IP address
IPv6: IP version 6 is a newer 128 bit IP address which allows for many more devices to be addressed
Address Hierarchy
There are two hierarchical addressing systems on the Internet: domain names and IP addresses. People use domain names (like sites.google.com) to visit websites. Computers that are part of the domain name system translate those domain names to IP addresses (like 128.32.189.18) to locate and send data behind the scenes.
A hierarchy is an arrangement of things with the biggest or highest category at the top and things ranked into subcategories below. A hierarchy is often depicted as a triangle.
For example, in a school, the principal is at the top, the department chairs oversee the teachers, and the teachers lead the students. In biology, we use a taxonomic hierarchy: kingdom, phylum, class, order, family, genus, species. And on computers, we store files in a hierarchy of folders within folders.
Before the Internet, there were only small networks of computers (like the Arpanet, which peaked at around 200 computers), and every computer knew the name of all the other computers on the network. That worked for small networks, but it's not realistic for the 3 billion computers on the Internet now. So now, a hierarchy allows the system to distribute requests for IP addresses to domain name servers across the growing network.
Domain Name Hierarchy
Recall the structure of a URL:
Just as the path in a URL locates a specific file in a hierarchy of folders on the server, domain names locate a specific website within a hierarchical domain name system (DNS). The hierarchy of the domain name system simplifies the process of finding the computer with the desired domain name because the DNS servers that help locate domains don't need enormous lists with every host name in the world. Instead, any user's computer only has to know where to find a root domain server (the one that knows where to find the top-level domains such as .org and .edu), and that server knows where to find the domain (like google.com), and that server knows where its subdomains are (like sites.google.com), and so on.
The root domain may be a country code (such as .mx for Mexico) or a category code (like .gov for government). The last two segments of a domain name (like google.com) make up the primary domain, the main address for a site. Subdomains are subsections of primary domains or of other subdomains. For example:
sites.google.com and classroom.google.com are both subdomains of google.com
store.parks.ca.gov is a subdomain of ca.gov
This image at is a simplified model of domain name hierarchy:
IP Address Hierarchy
This image is a simplified model of IP address hierarchy.
When we type in a domain name, the browser queries the domain name system to find the Internet Protocol (IP) address of the server we want to visit. IP addresses are unique numerical addresses assigned to every device on the Internet. Both the domain name syntax and IP addresses are hierarchical; however unlike domain names, with IP addresses, the individual site is on the right and the top-level groupings are on the left).
Still Curious?
There is a wealth of good introductory and comprehensive information about the Internet and the WWW.
As always, Wikipedia is an excellent resource as a first stop. Its pages on Internet protocol, Ping, Traceroute, and the other topics in this lesson are all accurate and accessible. Wikipedia's entry on the Internet.
The How Stuff Works site has a nice animated description of how routers work to direct traffic on the Internet.
Warriors of the Net is a classic 12 minute animated video about packets traveling through the Internet.
For a very detailed and comprehensive discussion of networking, sort of like reading a short book, see the CTDP's Networking Tutorial, which covers the topic in much more detail than we have done here.
Explore this map of the underwater cables that carry 99% of international data. (2016 interactive version of map)
Watch this video that describes how a hacker could view your data on a public network using a packet sniffer.