<Tr> <Td> IXFR </Td> <Td> 251 </Td> <Td> RFC 1996 </Td> <Td> Incremental Zone Transfer </Td> <Td> Requests a zone transfer of the given zone but only differences from a previous serial number . This request may be ignored and a full (AXFR) sent in response if the authoritative server is unable to fulfill the request due to configuration or lack of required deltas . </Td> </Tr> <Tr> <Td> OPT </Td> <Td> 41 </Td> <Td> RFC 6891 </Td> <Td> Option </Td> <Td> This is a "pseudo DNS record type" needed to support EDNS </Td> </Tr> <P> Progress has rendered some of the originally defined record - types obsolete . Of the records listed at IANA, some have limited use, for various reasons . Some are marked obsolete in the list, some are for very obscure services, some are for older versions of services, and some have special notes saying they are "not right". </P> <Table> <Tr> <Th> Type </Th> <Th> Type id . </Th> <Th> Defining RFC </Th> <Th> Obsoleted by </Th> <Th> Description </Th> </Tr> <Tr> <Td> MD <P> MF </P> <P> MAILA </P> </Td> <Td> <P> </P> <P> 254 </P> </Td> <Td> RFC 973 </Td> <Td> Obsoleted by: 1034, 1035 </Td> <Td> Obsoleted by RFC 973: MD (3), MF (4), MAILA (254) </Td> </Tr> <Tr> <Td> MB <P> MG </P> <P> MR </P> <P> MINFO </P> <P> MAILB </P> </Td> <Td> 7 <P> 8 </P> <P> 9 </P> <P> 14 </P> <P> 253 </P> </Td> <Td> RFC 883, RFC 2505 </Td> <Td> Obsoleted by: 1034, 1035 <P> Obsoleted by: 2050 </P> </Td> <Td> Records to publish mailing list subscriber lists in the DNS: MB (7), MG (8), MR (9), MINFO (14), MAILB (253). The intent, as specified by RFC 883, was for MB to replace the SMTP VRFY command, MG to replace the SMTP EXPN command, and MR to replace the "551 User Not Local" SMTP error . Later, RFC 2505 recommended that both the VRFY and EXPN commands be disabled, making the use of MB and MG unlikely to ever be adopted . </Td> </Tr> <Tr> <Td> WKS </Td> <Td> 11 </Td> <Td> RFC 1123 </Td> <Td> </Td> <Td> Declared "not to be relied upon" by RFC 1123 (with further information in RFC 1127): WKS (11) </Td> </Tr> <Tr> <Td> NB <P> NBSTAT </P> </Td> <Td> 32 <P> 33 </P> </Td> <Td> RFC 1002 </Td> <Td> </Td> <Td> Mistakes: NB (32), NBSTAT (33) (from RFC 1002); the numbers are now assigned to NIMLOC and SRV . </Td> </Tr> <Tr> <Td> NULL </Td> <Td> 0 </Td> <Td> RFC 883 </Td> <Td> RFC 1035 </Td> <Td> Obsoleted by RFC 1035: NULL (10) (RFC 883 defined "completion queries" (opcode 2 and maybe 3) which used this record, RFC 1035 later reassigned opcode 2 to be "status" and reserved opcode 3 .) </Td> </Tr> <Tr> <Td> A6 </Td> <Td> 38 </Td> <Td> RFC 3363 </Td> <Td> RFC 6563 </Td> <Td> Defined as part of early IPv6 but downgraded to experimental by RFC 3363: A6 (38), Later downgraded to historic in RFC 6563 . </Td> </Tr> <Tr> <Td> NXT <P> KEY </P> <P> SIG </P> </Td> <Td> 30 <P>--</P> <P>--</P> </Td> <Td> RFC 3755 </Td> <Td> RFC 4034 </Td> <Td> Obsoleted by DNSSEC updates (RFC 3755): NXT (30). At the same time, the domain of applicability for KEY and SIG was also limited to not include DNSSEC use . </Td> </Tr> <Tr> <Td> </Td> <Td> </Td> <Td> RFC 2065 </Td> <Td> </Td> <Td> Part of the first version of DNSSEC (RFC 2065). </Td> </Tr> <Tr> <Td> HINFO </Td> <Td> 13 </Td> <Td> </Td> <Td> </Td> <Td> Not in current use by any notable application </Td> </Tr> <Tr> <Td> RP </Td> <Td> 17 </Td> <Td> </Td> <Td> </Td> <Td> RP may be used for certain human - readable information regarding a different contact point for a specific host, subnet, or other domain level label separate than that used in the SOA record . </Td> </Tr> <Tr> <Td> X25 </Td> <Td> 19 </Td> <Td> </Td> <Td> </Td> <Td> Not in current use by any notable application </Td> </Tr> <Tr> <Td> ISDN <P> RT </P> <P> NSAP </P> </Td> <Td> 20 <P> 21 </P> <P> 22 </P> </Td> <Td> </Td> <Td> </Td> <Td> Not in current use by any notable application </Td> </Tr> <Tr> <Td> NSAP - PTR <P> PX </P> <P> EID </P> </Td> <Td> 23 <P> 26 </P> <P> 31 </P> </Td> <Td> </Td> <Td> </Td> <Td> Not in current use by any notable application </Td> </Tr> <Tr> <Td> NIMLOC <P> ATMA </P> <P> APL </P> </Td> <Td> 32 <P> 34 </P> <P> 42 </P> </Td> <Td> </Td> <Td> </Td> <Td> Not in current use by any notable application </Td> </Tr> <Tr> <Td> SINK </Td> <Td> 40 </Td> <Td> </Td> <Td> </Td> <Td> Defined by the Kitchen Sink internet draft, but never made it to RFC status: SINK (40) </Td> </Tr> <Tr> <Td> GPOS </Td> <Td> 27 </Td> <Td> </Td> <Td> </Td> <Td> A more limited early version of the LOC record: GPOS (27) </Td> </Tr> <Tr> <Td> UINFO <P> UID </P> <P> GID </P> <P> UNSPEC </P> </Td> <Td> 100 <P> 101 </P> <P> 102 </P> <P> 103 </P> </Td> <Td> </Td> <Td> </Td> <Td> IANA reserved, no RFC documented them (1) and support was removed from BIND in the early 90s: UINFO (100), UID (101), GID (102), UNSPEC (103) </Td> </Tr> <Tr> <Td> SPF </Td> <Td> 99 </Td> <Td> RFC 4408 </Td> <Td> </Td> <Td> SPF (99) (from RFC 4408) was specified as part of the Sender Policy Framework protocol as an alternative to storing SPF data in TXT records, using the same format . It was later found that the majority of SPF deployments lack proper support for this record type, and support for it was discontinued in RFC 7208 . </Td> </Tr> </Table>

What are some of the most common dns records used to perform a dns query