From http://www.iana.org/assignments/dns-parameters (last updated 11 July 2005) A 1 a host address [RFC1035] NS 2 an authoritative name server [RFC1035] MD 3 a mail destination (Obsolete - use MX) [RFC1035] MF 4 a mail forwarder (Obsolete - use MX) [RFC1035] CNAME 5 the canonical name for an alias [RFC1035] SOA 6 marks the start of a zone of authority [RFC1035] MB 7 a mailbox domain name (EXPERIMENTAL) [RFC1035] MG 8 a mail group member (EXPERIMENTAL) [RFC1035] MR 9 a mail rename domain name (EXPERIMENTAL)[RFC1035] NULL 10 a null RR (EXPERIMENTAL) [RFC1035] WKS 11 a well known service description [RFC1035] PTR 12 a domain name pointer [RFC1035] HINFO 13 host information [RFC1035] MINFO 14 mailbox or mail list information [RFC1035] MX 15 mail exchange [RFC1035] TXT 16 text strings [RFC1035] RP 17 for Responsible Person [RFC1183] AFSDB 18 for AFS Data Base location [RFC1183] X25 19 for X.25 PSDN address [RFC1183] ISDN 20 for ISDN address [RFC1183] RT 21 for Route Through [RFC1183] NSAP 22 for NSAP address, NSAP style A record [RFC1706] NSAP-PTR 23 SIG 24 for security signature [RFC2535], [RFC3755], [RFC4034] KEY 25 for security key [RFC2535], [RFC3755], [RFC4034] PX 26 X.400 mail mapping information [RFC2163] GPOS 27 Geographical Position [RFC1712] AAAA 28 IP6 Address [Thomson] LOC 29 Location Information [Vixie] NXT 30 Next Domain - OBSOLETE [RFC2535, RFC3755] EID 31 Endpoint Identifier [Patton] NIMLOC 32 Nimrod Locator [Patton] SRV 33 Server Selection [RFC2782] ATMA 34 ATM Address [Dobrowski] NAPTR 35 Naming Authority Pointer [RFC2168, RFC2915] KX 36 Key Exchanger [RFC2230] CERT 37 CERT [RFC2538] A6 38 A6 [RFC2874] DNAME 39 DNAME [RFC2672] SINK 40 SINK [Eastlake] OPT 41 OPT [RFC2671] APL 42 APL [RFC3123] DS 43 Delegation Signer [RFC3658] SSHFP 44 SSH Key Fingerprint [RFC-ietf-secsh-dns-05.txt] IPSECKEY 45 IPSECKEY [RFC4025] RRSIG 46 RRSIG [RFC3755] NSEC 47 NSEC [RFC3755] DNSKEY 48 DNSKEY [RFC3755] SPF 99 [RFC-schlitt-spf-classic-02.txt] UINFO 100 [IANA-Reserved] UID 101 [IANA-Reserved] GID 102 [IANA-Reserved] UNSPEC 103 [IANA-Reserved] TKEY 249 Transaction Key [RFC2930] TSIG 250 Transaction Signature [RFC2845] IXFR 251 incremental transfer [RFC1995] AXFR 252 transfer of an entire zone [RFC1035] MAILB 253 mailbox-related RRs (MB, MG or MR) [RFC1035] MAILA 254 mail agent RRs (Obsolete - see MX) [RFC1035] * 255 A request for all records [RFC1035]