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                           9  DNS Messaging and Message, Resource Record and Master File Formats

DNS Message Header and Question Section Format 1 2 3 4 5 DNS Name Notation and Message Compression Technique

The exchange of information in DNS consists of a series of client/server transactions. Clients send requests, or queries, to servers, and the servers send back responses. DNS servers are of course database servers, and store DNS name database information in the form of resource records (RRs). The questions asked by clients are requests for information from a DNS's servers database, and they are answered by the DNS server looking up the requested resource records and putting them into the DNS response message.

The Answer, Authority and Additional sections of the overall DNS message format are the places where servers put DNS resource records to be sent back to a client. Each section consists of zero or more records, and in theory, any record can be placed in any section. The sections only differ in the semantics (meaning) that the client draws from a record being in one section compared to the other. The topic on DNS general messaging contains more on these three sections and how they are used.

Resource records have two representations: binary and text. The text format is used for master files edited by humans, and is the subject of a topic later in this section. The binary representation consists of regular numeric and text fields just like the other fields in the DNS message format.

DNS Message Header and Question Section Format 1 2 3 4 5 DNS Name Notation and Message Compression Technique