Book Image

DNS in Action

By : CP Books a.s.
Book Image

DNS in Action

By: CP Books a.s.

Overview of this book

The Domain Name System is one of the foundations of the internet. It is the system that allows the translation of human-readable domain names into machines-readable IP addresses and the reverse translation of IP addresses into domain names. This book describes the basic DNS protocol and its extensions; DNS delegation and registration, including for reverse domains; using DNS servers in networks that are not connected to the internet; and using DNS servers on firewall machines. Many detailed examples are used throughout the book to show perform various configuration and administration tasks.
Table of Contents (16 chapters)
DNS in Action
About the Authors
Country Codes and RIRs

1.6 Reserved Domains and Pseudodomains

It was later decided that other domains could also be used as TLD. Some TLD were reserved in RFC 2606:

  • The test domain for testing

  • The example domain for creating documentation and examples

  • The invalid domain for evoking error states

  • The localhost domain for software loops

Domains that are not directly connected to the Internet can also exist, i.e., computers that do not even use the TCP/IP network protocol therefore do not have an IP address. These domains are sometimes called pseudodomains. They are meaningful especially for electronic mail. It is possible to send an email into other networks and then into the Internet with the help of a pseudodomain (like DECnet or MS Exchange).

In its internal network, a company can first use TCP/IP and then DECnet protocol. A user using TCP/IP in the internal network (for example,) is addressed from the Internet. But how do you address a user on computers working in the DECnet protocol?

To solve this, we insert the fictive dnet pseudodomain into the address. The user Daniel is therefore addressed [email protected]. With the help of DNS, the entire email that was addressed into the domain is redirected to a gateway in DECnet protocol (the gateway of the domain), which performs the transformation from TCP/IP (for SMTP) into DECnet (for Mail-11).