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The octets serve a purpose other than simply separating the numbers. They are used to create classes of IP addresses that can be assigned to a particular business, government or other entity based on size and need. The octets are split into two sections: Net and Host. The Net section always contains the first octet. It is used to identify the network that a computer belongs to. Host (sometimes referred to as Node) identifies the actual computer on the network. The Host section always contains the last octet. There are five IP classes plus certain special addresses.
When the Internet was in its infancy, it consisted of a small number of computers hooked together with modems and telephone lines. You could only make connections by providing the IP address of the computer you wanted to establish a link with. For example, a typical IP address might be 216.27.22.162. This was fine when there were only a few hosts out there, but it became unwieldy as more and more systems came online.
The first solution to the problem was a simple text file maintained by the Network Information Center that mapped names to IP addresses. Soon this text file became so large it was too cumbersome to manage. In 1983, the University of Wisconsin created the Domain Name System (DNS), which maps text names to IP addresses automatically. This way you only need to remember http://www.genesistelemanagement.com for example, instead of genesistelemanagement.com's IP address.
What's In A Name?
When you use the Web or send an e-mail message, you use a domain name to do it. For example, the Uniform Resource Locator (URL) "http://www.genesistelemanagement.com/" contains the domain name genesistelemanagement.com. So does this e-mail address: brain@genesistelemanagement.com . Every time you use a domain name, you use the Internet's DNS servers to translate the human-readable domain name into the machine-readable IP address.
Top-level domain names, also called first-level domain names, include .COM, .ORG, .NET, .EDU and .GOV. Within every top-level domain there is a huge list of second-level domains. Every name in the COM top-level domain must be unique. The left-most word, like www, is the host name. It specifies the name of a specific machine (with a specific IP address) in a domain. A given domain can, potentially, contain millions of host names as long as they are all unique within that domain.
DNS servers accept requests from programs and other name servers to convert domain names into IP addresses. When a request comes in, the DNS server can do one of four things with it:
- It can answer the request with an IP address because it already knows the IP address for the requested domain.
- It can contact another DNS server and try to find the IP address for the name requested. It may have to do this multiple times.
- It can say, "I don't know the IP address for the domain you requested, but here's the IP address for a DNS server that knows more than I do."
- It can return an error message because the requested domain name is invalid or does not exist.
Let's say that you type the URL http://www.genesistelemanagement.com into your browser. The browser contacts a DNS server to get the IP address. A DNS server would start its search for an IP address by contacting one of the root DNS servers. The root servers know the IP addresses for all of the DNS servers that handle the top-level domains (COM, NET, ORG, etc.). Your DNS server would ask the root for www.genesistelemanagement.com, and the root would say, "I don't know the IP address for www.genesistelemanagement.com but here's the IP address for the COM DNS server."
Your name server then sends a query to the COM DNS server asking it if it knows the IP address for www.genesistelemanagement.com. The DNS server for the COM domain knows the IP addresses for the name servers handling the http://www.genesistelemanagement.com domain, so it returns those.
Your name server then contacts the DNS server for http://www.genesistelemanagement.com and asks if it knows the IP address for http://www.genesistelemanagement.com/. It actually does, so it returns the IP address to your DNS server, which returns it to the browser, which can then contact the server for http://www.genesistelemanagement.com/ to get a Web page.
One of the keys to making this work is redundancy. There are multiple DNS servers at every level, so that if one fails, there are others to handle the requests. The other key is caching. Once a DNS server resolves a request, it caches the IP address it receives. Once it has made a request to a root DNS server for any COM domain, it knows the IP address for a DNS server handling the COM domain, so it doesn't have to bug the root DNS servers again for that information. DNS servers can do this for every request, and this caching helps to keep things from bogging down.
Even though it is totally invisible, DNS servers handle billions of requests every day and they are essential to the Internet's smooth functioning. The fact that this distributed database works so well and so invisibly day in and day out is a testimony to the design.
Web Servers
Internet servers make the Internet possible. All of the machines on the Internet are either servers or clients. The machines that provide services to other machines are servers. And the machines that are used to connect to those services are clients. There are Web servers, e-mail servers, FTP servers and so on serving the needs of Internet users all over the world.
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