Asking for Name Resolution Help Inside the Company

Asking for Name Resolution Help Inside the Company

When you use directory assistance in the U.S., you pick up the phone and dial 411. To use DNS inside a single company, each TCP/IP host asks for help from a computer that is running a service called a DNS server. For the process to work, two key facts must be true:

The DNS server is a computer that is running DNS server software. The DNS server has a list of all the TCP/IP host names in the network, along with their corresponding IP addresses. You can think of the list as the same general concept as a local host table, but instead of needing a copy on every host computer, there's one copy on the DNS server. Keeping one copy of the list of names and IP addresses current is much easier than having everyone in the company try to do the same! As you'll learn more about in the section titled "Asking for Name Resolution Help Outside the Company," a DNS server doesn't need to know all the names and IP addresses in the Internet, but just a small portion of them.

To support DNS, each TCP/IP host needs to know the IP address of the DNS server. It's similar to the idea that everyone in the U.S. knows to dial 411 to get telephone directory assistance. In this case, the DNS server's IP address is 150.1.3.4, and Hannah needs to know that address before she can send packets to the server.

Hannah's PC has two ways of knowing the DNS server's IP address. First, the address might be statically configured at Hannah's PC. Alternatively, Hannah might dynamically learn that address using the DHCP protocol, as mentioned in Chapter 10, "Delivering the Goods to the Right Street (IP) Address." Regardless of how Hannah knows that her DNS is at 150.1.3.4, she must know that fact ahead of time.

The main concept is simple, as shown in Figure 13-2. This time, Hannah is inside the fictitious example.com corporation's enterprise network.