Domain Name System (DNS) Parameters

Last Updated
Available Formats



Plain text

Registries included below


As noted in [RFC6762], Multicast DNS can only carry DNS records with classes in the range 0-32767. 
Classes in the range 32768 to 65535 are incompatible with Multicast DNS.
Available Formats

Decimal Hex Registration Procedures Note
0 0x0000 Standards Action
1-127 0x0000-0x007F IETF Review data CLASSes only
128-253 0x0080-0x00FD IETF Review QCLASSes and meta-CLASSes only
256-32767 0x0100-0x7FFF IETF Review
32768-57343 0x8000-0xDFFF Specification Required data CLASSes only
57344-65279 0xE000-0xFEFF Specification Required QCLASSes and meta-CLASSes only
65280-65534 0xFF00-0xFFFE Reserved for Private Use
65535 0xFFFF Standards Action
Decimal Hexadecimal Name Reference
0 0x0000 Reserved [RFC6895]
1 0x0001 Internet (IN) [RFC1035]
2 0x0002 Unassigned
3 0x0003 Chaos (CH) [D. Moon, "Chaosnet", A.I. Memo 628, Massachusetts Institute of Technology Artificial Intelligence Laboratory, June 1981.]
4 0x0004 Hesiod (HS) [Dyer, S., and F. Hsu, "Hesiod", Project Athena Technical Plan - Name Service, April 1987.]
5-253 0x0005-0x00FD Unassigned
254 0x00FE QCLASS NONE [RFC2136]
255 0x00FF QCLASS * (ANY) [RFC1035]
256-65279 0x0100-0xFEFF Unassigned
65280-65534 0xFF00-0xFFFE Reserved for Private Use [RFC6895]
65535 0xFFFF Reserved [RFC6895]

Resource Record (RR) TYPEs

Available Formats

Decimal Hex Registration Procedures Note
0 0x0000 RRTYPE zero is used as a special indicator for the SIG RR [RFC2931], [RFC4034] and in other circumstances and must never be allocated for ordinary use.
1-127 0x0000-0x007F DNS RRTYPE Allocation Policy data TYPEs
128-255 0x0080-0x00FF DNS RRTYPE Allocation Policy Q TYPEs, Meta TYPEs
256-61439 0x0100-0xEFFF DNS RRTYPE Allocation Policy data RRTYPEs
61440-65279 0xF000-0xFEFF IETF Review
65280-65534 0xFF00-0xFFFE Reserved for Private Use
65535 0xFFFF Reserved (Standards Action)
TYPE Value Meaning Reference Template Registration Date
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][RFC5864]
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 for domain name pointer, NSAP style [RFC1348][RFC1637][RFC1706]
SIG 24 for security signature [RFC4034][RFC3755][RFC2535][RFC2536][RFC2537][RFC2931][RFC3110][RFC3008]
KEY 25 for security key [RFC4034][RFC3755][RFC2535][RFC2536][RFC2537][RFC2539][RFC3008][RFC3110]
PX 26 X.400 mail mapping information [RFC2163]
GPOS 27 Geographical Position [RFC1712]
AAAA 28 IP6 Address [RFC3596]
LOC 29 Location Information [RFC1876]
NXT 30 Next Domain (OBSOLETE) [RFC3755][RFC2535]
EID 31 Endpoint Identifier [Michael_Patton][] 1995-06
NIMLOC 32 Nimrod Locator [1][Michael_Patton][] 1995-06
SRV 33 Server Selection [1][RFC2782]
ATMA 34 ATM Address [ ATM Forum Technical Committee, "ATM Name System, V2.0", Doc ID: AF-DANS-0152.000, July 2000. Available from and held in escrow by IANA.]
NAPTR 35 Naming Authority Pointer [RFC2915][RFC2168][RFC3403]
KX 36 Key Exchanger [RFC2230]
CERT 37 CERT [RFC4398]
A6 38 A6 (OBSOLETE - use AAAA) [RFC3226][RFC2874][RFC6563]
SINK 40 SINK [Donald_E_Eastlake][] 1997-11
OPT 41 OPT [RFC6891][RFC3225]
APL 42 APL [RFC3123]
DS 43 Delegation Signer [RFC4034][RFC3658]
SSHFP 44 SSH Key Fingerprint [RFC4255]
RRSIG 46 RRSIG [RFC4034][RFC3755]
NSEC 47 NSEC [RFC4034][RFC3755]
NSEC3 50 NSEC3 [RFC5155]
TLSA 52 TLSA [RFC6698]
Unassigned 53-54
HIP 55 Host Identity Protocol [RFC5205]
NINFO 56 NINFO [Jim_Reid] NINFO/ninfo-completed-template 2008-01-21
RKEY 57 RKEY [Jim_Reid] RKEY/rkey-completed-template 2008-01-21
TALINK 58 Trust Anchor LINK [Wouter_Wijngaards] TALINK/talink-completed-template 2010-02-17
CDS 59 Child DS [George_Barwood] CDS/cds-completed-template 2011-06-06
Unassigned 60-98
SPF 99 [RFC-ietf-spfbis-4408bis-21]
UINFO 100 [IANA-Reserved]
UID 101 [IANA-Reserved]
GID 102 [IANA-Reserved]
UNSPEC 103 [IANA-Reserved]
NID 104 [RFC6742] ILNP/nid-completed-template
L32 105 [RFC6742] ILNP/l32-completed-template
L64 106 [RFC6742] ILNP/l64-completed-template
LP 107 [RFC6742] ILNP/lp-completed-template
EUI48 108 an EUI-48 address [RFC7043] EUI48/eui48-completed-template 2013-03-27
EUI64 109 an EUI-64 address [RFC7043] EUI64/eui64-completed-template 2013-03-27
Unassigned 110-248
TKEY 249 Transaction Key [RFC2930]
TSIG 250 Transaction Signature [RFC2845]
IXFR 251 incremental transfer [RFC1995]
AXFR 252 transfer of an entire zone [RFC1035][RFC5936]
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 the server/cache has available [RFC1035][RFC6895]
URI 256 URI [Patrik_Faltstrom] URI/uri-completed-template 2011-02-22
CAA 257 Certification Authority Restriction [RFC6844] CAA/caa-completed-template 2011-04-07
Unassigned 258-32767
TA 32768 DNSSEC Trust Authorities [Sam_Weiler][][ Deploying DNSSEC Without a Signed Root. Technical Report 1999-19, Information Networking Institute, Carnegie Mellon University, April 2004.] 2005-12-13
DLV 32769 DNSSEC Lookaside Validation [RFC4431]
Unassigned 32770-65279
Private use 65280-65534
Reserved 65535

DNS OpCodes

Registration Procedure(s)
Standards Action
Available Formats

OpCode Name Reference
0 Query [RFC1035]
1 IQuery (Inverse Query, OBSOLETE) [RFC3425]
2 Status [RFC1035]
3 Unassigned
4 Notify [RFC1996]
5 Update [RFC2136]
6-15 Unassigned


Registration Procedure(s)
IETF Review
Available Formats

RCODE Name Description Reference
0 NoError No Error [RFC1035]
1 FormErr Format Error [RFC1035]
2 ServFail Server Failure [RFC1035]
3 NXDomain Non-Existent Domain [RFC1035]
4 NotImp Not Implemented [RFC1035]
5 Refused Query Refused [RFC1035]
6 YXDomain Name Exists when it should not [RFC2136][RFC6672]
7 YXRRSet RR Set Exists when it should not [RFC2136]
8 NXRRSet RR Set that should exist does not [RFC2136]
9 NotAuth Server Not Authoritative for zone [RFC2136]
9 NotAuth Not Authorized [RFC2845]
10 NotZone Name not contained in zone [RFC2136]
11-15 Unassigned
16 BADVERS Bad OPT Version [RFC6891]
16 BADSIG TSIG Signature Failure [RFC2845]
17 BADKEY Key not recognized [RFC2845]
18 BADTIME Signature out of time window [RFC2845]
19 BADMODE Bad TKEY Mode [RFC2930]
20 BADNAME Duplicate key name [RFC2930]
21 BADALG Algorithm not supported [RFC2930]
22 BADTRUNC Bad Truncation [RFC4635]
23-3840 Unassigned
3841-4095 Reserved for Private Use [RFC6895]
4096-65534 Unassigned
65535 Reserved, can be allocated by Standards Action [RFC6895]

AFSDB RR Subtype

Registration Procedure(s)
Registry closed per [RFC6895]
Available Formats

Decimal Hexadecimal Description Reference
0 0x0000 Reserved; registry closed [RFC6895]
1 0x0001 Andrews File Service v3.0 Location Service [RFC1183]
2 0x0002 DCE/NCA root cell directory node [RFC1183]
3-65279 0x0003-0xFEFF Not allocated; registry closed
65280-65534 0xFF00-0xFFFE Reserved for Private Use [RFC6895]
65535 0xFFFF Reserved; registry closed [RFC6895]

DHCID RR Identifier Type Codes

Registration Procedure(s)
Standards Action
Olafur Gudmundsson
Registration rules to be as follows:
New DHCID RR type codes are tentatively assigned after the specification for the associated type code,
published as an Internet Draft, has received expert review by a designated expert.
The final assignment of DHCID RR type codes is through Standards Action, as defined in [RFC2434].
Available Formats

Identifier Type Code Identifier Reference
0x0000 The 1-octet 'htype' followed by 'hlen' octets of 'chaddr' from a DHCPv4 client's DHCPREQUEST. [RFC4701]
0x0001 The data octets (i.e., the Type and Client-Identifier fields) from a DHCPv4 client's Client Identifier option. [RFC4701]
0x0002 The client's DUID (i.e., the data octets of a DHCPv6 client's Client Identifier option or the DUID field from a DHCPv4 client's Client Identifier option). [RFC4701]
0x0003-0xFFFE Unassigned [RFC4701]
0xFFFF Reserved [RFC4701]

DNS Label Types

Registration Procedure(s)
Standards Action
The top 2 bits of the first byte of an DNS label indicate the type of label.
Available Formats

Value Type Status Reference
0 0 Normal label lower 6 bits is the length of the label Standard [RFC1035]
1 1 Compressed label the lower 6 bits and the 8 bits from next octet form a pointer to the compression target. Standard [RFC1035]
0 1 Extended label type the lower 6 bits of this type (section 3) indicate the type of label in use Proposed [RFC6891]
0 1 0 0 0 0 0 1 Binary Label Historic [RFC3364][RFC3363][RFC2673][RFC6891]
0 1 1 1 1 1 1 1 Reserved for future expansion. Proposed [RFC6891]
1 0 Unallocated

DNS EDNS0 Option Codes (OPT)

Registration Procedure(s)
Expert Review
Olafur Gudmundsson
[RFC6891][RFC Errata 3604]
Available Formats

Value Name Status Reference
0 Reserved [RFC6891]
1 LLQ On-hold []
2 UL On-hold []
3 NSID Standard [RFC5001]
4 Reserved [draft-cheshire-edns0-owner-option]
5 DAU Standard [RFC6975]
6 DHU Standard [RFC6975]
7 N3U Standard [RFC6975]
8 edns-client-subnet Optional [draft-vandergaast-edns-client-subnet][Wilmer_van_der_Gaast]
9-65000 Unassigned
65001-65534 Reserved for Local/Experimental Use [RFC6891]
65535 Reserved for future expansion [RFC6891]

DNS Header Flags

Registration Procedure(s)
Standards Action
In DNS query header there is a flag field in the
second 16 bit word in query from bit 5 through
bit 11 ([RFC1035] section 4.1.1)
Available Formats

Bit Flag Description Reference
bit 5 AA Authoritative Answer [RFC1035]
bit 6 TC Truncated Response [RFC1035]
bit 7 RD Recursion Desired [RFC1035]
bit 8 RA Recursion Allowed [RFC1035]
bit 9 Reserved
bit 10 AD Authentic Data [RFC4035]
bit 11 CD Checking Disabled [RFC4035]

EDNS Header Flags (16 bits)

Registration Procedure(s)
Standards Action
Available Formats

Bit Flag Description Reference
Bit 0 DO DNSSEC answer OK [RFC4035][RFC3225]
Bit 1-15 Reserved

EDNS version Number (8 bits)

Registration Procedure(s)
Standards Action
Available Formats

Range Description Reference
0 EDNS version 0 [RFC6891]
1-255 Unassigned


ID Name Contact URI Last Updated
[Donald_E_Eastlake] Donald E. Eastlake, III mailto:d3e3e3& 1997-11
[George_Barwood] George Barwood mailto:george.barwood& 2011-06-06
[Jim_Reid] Jim Reid mailto:jim& 2008-01-21
[Michael_Patton] Michael Patton mailto:map& 1995-06
[Patrik_Faltstrom] Patrik Faltstrom mailto:paf& 2011-02-22
[Phillip_Hallam_Baker] Phillip Hallam-Baker mailto:phill& 2011-04-07
[Sam_Weiler] Sam Weiler mailto:weiler+iana& 2005-12
[Wilmer_van_der_Gaast] Wilmer van der Gaast mailto:wilmer& 2013-06-05
[Wouter_Wijngaards] Wouter Wijngaards mailto:wouter& 2010-02-17


In [RFC1002], two types are defined.  It is not clear that these
are in use, though if so their assignment does conflict with those above.
        NB      32      NetBIOS general Name Service
        NBSTAT  33      NetBIOS NODE STATUS