Asking for Name Resolution Help Outside the Company

Asking for Name Resolution Help Outside the Company

Your local telephone company has a list of all its customers and their local phone numbers. But there are a lot of people in the world who are not customers of your local telephone company, so those people won't be on your local phone company's list of names. However, these days, you can typically dial 411 in the U.S. and get help finding a phone number of someone anywhere in the country. But if you use one local phone company, say Bell South, and the person you are calling is a customer of Verizon, how can the Bell South directory assistance person help you find the phone number? As it turns out, the phone companies share information about the names and phone numbers so that they can each provide better customer service to their own local customers. In effect, the master list of names and phone numbers is distributed among lots of phone companies.

A similar kind of thing happens with DNS, although there are some underlying differences. Multiple DNS servers work together, with each DNS holding different sets of names and IP addresses. Figure 13-3 points out the need for DNS servers to cooperate to support name resolution for any name. In this case, Hannah is still in the example.com enterprise network, but now she wants to reach the http://www.fredsco.com website, which is located in the Fredsco enterprise network.