The TCP/IP Guide  9  TCP/IP Application Layer Protocols, Services and Applications (OSI Layers 5, 6 and 7)       9  Name Systems and TCP/IP Name Registration and Name Resolution            9  TCP/IP Name Systems: Host Tables and Domain Name System (DNS)                 9  TCP/IP Domain Name System (DNS)                      9  DNS Name Servers and Name Resolution

DNS Electronic Mail Support and Mail Exchange (MX) Resource Records 1 DNS Message Generation and Transport

Networking is all about the communication of information between connected devices. In the case of the Domain Name System, information about names and objects on the internetwork is exchanged during each of the many types of operations DNS performs. This involves sending messages between devices. Like most protocols, DNS uses its own set of messages with distinct field formats, and follows a particular set of rules for generating them and transporting them over the internetwork.

In this section I explain how messages are generated and sent in DNS, and also describe the formats used for messages and resource records. I begin with an overview discussion of DNS messages and how they are generated and transported. I provide an overview of the general DNS message format, and the five sections it contains. I describe the notation used for names and the special compression method that helps keep DNS messages down in size. I then show the fields in the DNS message header and question section. I illustrate the common field format used for all resource records, and the specific fields in the most important record types. I conclude with a description of the format used for DNS text master files.

DNS Electronic Mail Support and Mail Exchange (MX) Resource Records 1 DNS Message Generation and Transport