This RFC provides a detailed specification of the domain name system (DNS) and its protocol, assuming familiarity with the concepts discussed in "Domain Names - Concepts and Facilities" [RFC-1034]. The DNS is a flexible system that includes both official and experimental components, with new data types and behaviors expected in future extensions. The official protocol includes standard queries, responses, and Internet class RR data formats (e.g., host addresses). Definitions have changed since the previous RFC set, and some previous definitions are now obsolete. The document outlines common configurations for hosts participating in the DNS, including standalone resolvers, primary and secondary name servers, and shared databases. It also covers the structure of domain names, data transmission order, character case handling, and size limits. The DNS uses a hierarchical naming system with labels terminated by a null label representing the root. Resource records (RRs) are defined for various purposes, such as host addresses, name servers, mail exchangers, and more. The document specifies the format and usage of these RRs, including standard RRs like CNAME, HINFO, MX, SOA, PTR, and TXT. The IN-ADDR.ARPA domain is introduced for mapping IP addresses to host names, facilitating gateway location and network address resolution. The document also discusses the use of master files to define zones and the process of zone transfers. Messages in the DNS are structured into headers, question sections, answer sections, authority sections, and additional records. The DNS supports both datagram and virtual circuit transports, with UDP being preferred for queries due to lower overhead and better performance. TCP is recommended for zone transfers due to reliability requirements. The document provides guidelines for implementing name servers and resolvers, including query processing, zone refresh, and cache management. It also covers mail support, such as mail exchange binding and mailbox binding. Finally, the document includes references and a bibliography, along with an index for easy navigation.This RFC provides a detailed specification of the domain name system (DNS) and its protocol, assuming familiarity with the concepts discussed in "Domain Names - Concepts and Facilities" [RFC-1034]. The DNS is a flexible system that includes both official and experimental components, with new data types and behaviors expected in future extensions. The official protocol includes standard queries, responses, and Internet class RR data formats (e.g., host addresses). Definitions have changed since the previous RFC set, and some previous definitions are now obsolete. The document outlines common configurations for hosts participating in the DNS, including standalone resolvers, primary and secondary name servers, and shared databases. It also covers the structure of domain names, data transmission order, character case handling, and size limits. The DNS uses a hierarchical naming system with labels terminated by a null label representing the root. Resource records (RRs) are defined for various purposes, such as host addresses, name servers, mail exchangers, and more. The document specifies the format and usage of these RRs, including standard RRs like CNAME, HINFO, MX, SOA, PTR, and TXT. The IN-ADDR.ARPA domain is introduced for mapping IP addresses to host names, facilitating gateway location and network address resolution. The document also discusses the use of master files to define zones and the process of zone transfers. Messages in the DNS are structured into headers, question sections, answer sections, authority sections, and additional records. The DNS supports both datagram and virtual circuit transports, with UDP being preferred for queries due to lower overhead and better performance. TCP is recommended for zone transfers due to reliability requirements. The document provides guidelines for implementing name servers and resolvers, including query processing, zone refresh, and cache management. It also covers mail support, such as mail exchange binding and mailbox binding. Finally, the document includes references and a bibliography, along with an index for easy navigation.