This RFC describes the domain system and protocol, assuming familiarity with "Domain Names – Concepts and Facilities" [RFC-1034]. The domain system combines official protocol functions with experimental ones, allowing new data types and behaviors. Official protocol parts include standard queries, responses, and Internet class RR formats. Experimental or obsolete features are marked, and example values should not be relied upon. The domain name space and RR definitions are detailed, including name space definitions, RR formats, and standard RRs like CNAME, HINFO, MX, and TXT. ARPA Internet-specific RRs, such as A and WKS, are also described. The IN-ADDR.ARPA domain supports host address to name mapping. New types, classes, and namespaces can be defined. Messages have a standardized format with header, question, answer, authority, and additional sections. Transport uses UDP for queries and TCP for zone transfers. Master files define zones with text-based RRs, including TTL, class, type, and RDATA. The format includes control entries like $ORIGIN and $INCLUDE, and special handling for domain names and character strings. The domain system ensures reliability through replication and redundancy, with careful handling of case, data transmission order, and size limits.This RFC describes the domain system and protocol, assuming familiarity with "Domain Names – Concepts and Facilities" [RFC-1034]. The domain system combines official protocol functions with experimental ones, allowing new data types and behaviors. Official protocol parts include standard queries, responses, and Internet class RR formats. Experimental or obsolete features are marked, and example values should not be relied upon. The domain name space and RR definitions are detailed, including name space definitions, RR formats, and standard RRs like CNAME, HINFO, MX, and TXT. ARPA Internet-specific RRs, such as A and WKS, are also described. The IN-ADDR.ARPA domain supports host address to name mapping. New types, classes, and namespaces can be defined. Messages have a standardized format with header, question, answer, authority, and additional sections. Transport uses UDP for queries and TCP for zone transfers. Master files define zones with text-based RRs, including TTL, class, type, and RDATA. The format includes control entries like $ORIGIN and $INCLUDE, and special handling for domain names and character strings. The domain system ensures reliability through replication and redundancy, with careful handling of case, data transmission order, and size limits.