Overview
IP addresses and network programs go hand in hand. When writing socket programs, you must indicate the IP address of either the local host for server applications, or a remote host for client applications. Sometimes this is not an easy thing to do—equating IP addresses and hostnames can be complicated. If all we ever needed were IP addresses, life would be a lot simpler for the network programmer.
In the real world, however, everywhere you look—books, magazines, websites, television advertisements, and all the rest—you see hostnames thrown at you. The Internet has made the hostname a common household item. Because of this, almost all network programs must allow customers to enter hostnames as well as IP addresses, and it is up to the network programmer to ensure that the program can find the IP address that is properly associated with the hostname. The primary control mechanism for accomplishing this is the Domain Name System (DNS), which is used to control hostnames and provide information to hosts wanting to find the IP address of another hostname.
Back in the old days (the ’80s) when the Internet was small, it wasn’t too hard to locate other computers on the network. Each system on the Internet contained a database that matched hostnames with assigned IP addresses. Internet hostnames could be anything the system administrator wanted to use—Fred, Barney, acctg1, anything. A central clearinghouse kept track of all the hostnames and IP addresses used on the Internet and published a master database containing all the address information. Usually once a week or so, individual system administrators downloaded the master database of hostnames and addresses to their local systems.
This system worked fine for a while, but it wasn’t long before it didn’t scale very well. As more and more hosts were added to the Internet, the database grew. And of course, as it grew, the longer it took to download, and the more space it took up on the individual systems. Clearly a dramatic improvement was needed, and that improvement was the Domain Name System (DNS).
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