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Lesson 1

Domain Name Service

The Domain Name Service (DNS) is an Internet-wide service for converting numeric IP addresses to host names and back. It may also be used on networks without an Internet connection; indeed, setting up DNS is a worthwhile investment, because it simplifies integrating a local network into the Internet when a connection becomes available.
By the end of this module, you will be able to:

  1. Describe the organization of the DNS namespace
  2. Define the top-level subdomains of the DNS
  3. Describe the process of converting IP addresses into names
  4. Define the concept of zones as used in the DNS namespace
  5. Describe the three classes of name servers
  6. List the steps required when a name server sends a query up the DNS hierarchy
  7. Describe the purpose and usefulness of caching-only name servers
  8. Identify the types of Resource Records
  9. Describe the general format of a zone file
  10. Describe the format of SOA, A, PTR, HINFO, CNAME, and NS records



Domain Name Servers (DNS) are the Internet's equivalent of a phone book. The DNS maintains a directory of domain names and translates them to (IP) Internet Protocol addresses. This is necessary because, although domain names are easy for people to remember, computers or machines, access websites by means of IP addresses.
Information from all the domain name servers across the Internet are gathered together and housed at the Central Registry. Host companies and Internet Service Providers interact with the Central Registry on a regular schedule to get updated DNS information. When you type in a web address, i.e., www.distributednetworks.com, your Internet Service Provider
  1. views the DNS associated with the domain name,
  2. translates it into a machine friendly IP address and
  3. directs your Internet connection to the correct website.
After you register a new domain name or when you update the DNS servers on your domain name, it usually takes about 12-24 hours for the domain name servers world-wide to be updated and able to access the information. This 24-hour period is referred to as the propagation period.