A resource record, commonly referred to as an RR, is the unit of information entry in DNS zone files; RRs are the basic building blocks of host-name and IP information and are used to resolve all DNS queries. Resource records come in a fairly wide variety of types in order to provide extended name-resolution services.
TYPE fields are used in DNS Resource Records (RRs) to specifiy the clas of the data in the RDATA field.
The RDATA field is a variable length field that describes the resource. The format of this information varies according to the TYPE and CLASS of the resource record.
|IN||1 (0x0001)||RFC 1035||The Internet||Active|
|CS||2 (0x0002)||RFC 1035||The CSNET||Obsolete|
|CH||3 (0x0003)||RFC 1035||The Chaos class||Limited|
|HS||4 (0x0004)||RFC 1035||The Hesiod [Dyer 87] class||Limited|
IN: The Internet
This is the most common class used when defining DNS Resource Records (RRs).
The 'CS' (Computer Science Network (CSNET)) was a computer network that began operation in 1981 in the United States. Its purpose was to extend networking benefits, for computer science departments at academic and research institutions that could not be directly connected to ARPANET, due to funding or authorization limitations. It played a significant role in spreading awareness of, and access to, national networking and was a major milestone on the path to development of the global Internet. CSNET was funded by the National Science Foundation for an initial three-year period from 1981 to 1984. More Info
The 'CH' class has its use in the Chaosnet, which is a network implementation that didn’t make it, unlike the current Ethernet + TCP/IP combo.
HS: Hesiod [Dyer 87]
The 'HS' class has its origins Project Athena. Which is a naming server ala NIS or more recent LDAP. With the HS class you can put user and group data in your DNS similar to LDAP. The hesiod package can still be installed if you are intrested in learning more.
- RFC 2929: Domain Name System (DNS) IANA Considerations
- Internet-Draft: The DNS Is Not Classy: DNS Classes Considered Useless