DNS Resource Records


DNS Resource Records are the basic information elements of the Domain Name System.

Each DNS Resource Records has a type (name and number), an Expiration Date (time to live), a class, and type-specific data.

DNS Resource Records of the same type are described as a resource record set (RRset). The order of resource records in a set, which is returned by a DNS resolvers to an application, is undefined, but often servers implement round-robin ordering to achieve load balancing. The Domain Name System Security Extensions (DNSSEC), however, work on the complete set of resource record in canonical order.

Resource record (RR) fields

FieldDescriptionLength (Octet)
NAMEName of the node to which this record pertainsVariable
TYPEDNS record type of RR in numeric form (e.g., 15 for MX RRs)2
CLASSClass code2
TTLCount of seconds that the RR stays valid (The maximum is 231−1, which is about 68 years)4
RDLENGTHLength of RDATA field2
RDATAAdditional RR-specific dataVariable, as per RDLENGTH


Domain Name System (DNS)

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