The TCP/IP Guide - DNS Overview, History and Standards

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TCP/IP and the Internet have both changed a lot since 1987, of course, and DNS has also had to change to suit. Many RFCs have been written since the base documents were published in the late 1980s, most of which further clarify the operation of DNS, expand on its capabilities, or define new features for it. You can find all of these by searching for “domain” or “DNS” in a list of RFCs. There are dozens of these, and I see no point in simply listing them all here, but I have highlighted a few of the more interesting ones in Table 164.

**Table 164: Additional DNS Standards**
RFC Number	Name	Description
1183	New DNS RR Definitions	Defines several new “experimental” resource record types. Other subsequent RFCs have also defined new RRs.
1794	DNS Support For Load Balancing	Discusses load balancing for greater performance in DNS servers.
1995	Incremental Zone Transfer in DNS	Specifies a new feature that allows only part of a zone to be transferred to a secondary name server for efficiency.
1996	A Mechanism for Prompt Notification of Zone Changes (DNS NOTIFY)	Adds a new message type to DNS to allow primary (authoritative) DNS servers to tell secondary servers that information has changed in the main database.
2136	Dynamic Updates in the Domain Name System (DNS UPDATE)	Describes a technique for dynamically making resource record changes in the DNS database (also called Dynamic DNS).
2181	Clarifications to the DNS Specification	Discusses several issues with the main DNS standards as defined in RFCs 1034 and 1035 and how to address them.
2308	Negative Caching of DNS Queries (DNS NCACHE)	Specifies the operation of negative caching, a feature that allows a server to maintain information about names that do not exist more efficiently.

IP version 6 was developed starting in the mid-1990s, and brought with it the need to make changes and enhancements to the operation of DNS. (Even though DNS operates at the higher layers, it deals intimately with addresses, and addresses have changed in IPv6.) The modifications required to DNS to support IPv6 were first defined in RFC 1886, IPv6 DNS Extensions, which was part of a group of RFCs that laid out the fundamentals of IPv6. Several subsequent standards have been published since that time; these are discussed in the topic on IPv6 DNS.

The three topics following in this section provide a more complete overview of DNS and its development, by discussing the design goals of its creators, and the protocol's key characteristics.