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

Roy Arends, Frederico AC Neves, Olafur Gudmundsson, Ray Bellis
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 Expert Review (see mailing list information in [RFC6895]) or Standards Action data TYPEs
128-255 0x0080-0x00FF Expert Review (see mailing list information in [RFC6895]) or Standards Action Q TYPEs, Meta TYPEs
256-61439 0x0100-0xEFFF Expert Review (see mailing list information in [RFC6895]) or Standards Action data RRTYPEs
61440-65279 0xF000-0xFEFF Reserved for future use (IETF Review required to define use)
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]
SMIMEA 53 S/MIME cert association [RFC8162] SMIMEA/smimea-completed-template 2015-12-01
Unassigned 54
HIP 55 Host Identity Protocol [RFC8005]
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 [RFC7344] CDS/cds-completed-template 2011-06-06
CDNSKEY 60 DNSKEY(s) the Child wants reflected in DS [RFC7344] 2014-06-16
OPENPGPKEY 61 OpenPGP Key [RFC7929] OPENPGPKEY/openpgpkey-completed-template 2014-08-12
CSYNC 62 Child-To-Parent Synchronization [RFC7477] 2015-01-27
ZONEMD 63 message digest for DNS zone [draft-wessels-dns-zone-digest] ZONEMD/zonemd-completed-template 2018-12-12
Unassigned 64-98
SPF 99 [RFC7208]
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 some or all records the server has available [RFC1035][RFC6895][RFC8482]
URI 256 URI [RFC7553] URI/uri-completed-template 2011-02-22
CAA 257 Certification Authority Restriction [RFC6844] CAA/caa-completed-template 2011-04-07
AVC 258 Application Visibility and Control [Wolfgang_Riedel] AVC/avc-completed-template 2016-02-26
DOA 259 Digital Object Architecture [draft-durand-doa-over-dns] DOA/doa-completed-template 2017-08-30
AMTRELAY 260 Automatic Multicast Tunneling Relay [draft-ietf-mboned-driad-amt-discovery] AMTRELAY/amtrelay-completed-template 2019-02-06
Unassigned 261-32767
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 DNS Stateful Operations (DSO) [RFC8490]
7-15 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 DSOTYPENI DSO-TYPE Not Implemented [RFC8490]
12-15 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 BADCOOKIE Bad/missing Server Cookie [RFC7873]
24-3840 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]

DHCID RR Digest Type Codes

Registration Procedure(s)
Standards Action
Available Formats

Digest Type Code Description Reference
0 Reserved [RFC4701]
1 SHA-256 [RFC4701]
2-255 Unassigned

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]
Registrations made by standards-track documents are listed as "Standard," 
and by non-standards-track documents as "Optional." Registrations for 
which there are no final specifications are listed as "On-Hold."
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 [RFC7871]
9 EDNS EXPIRE Optional [RFC7314]
10 COOKIE Standard [RFC7873]
11 edns-tcp-keepalive Standard [RFC7828]
12 Padding Standard [RFC7830]
13 CHAIN Standard [RFC7901]
14 edns-key-tag Optional [RFC8145]
15-26945 Unassigned
26946 DeviceID Optional [][Brian_Hartvigsen]
26947-65000 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 Available [RFC1035]
bit 9 Reserved
bit 10 AD Authentic Data [RFC4035][RFC6840][RFC Errata 4924]
bit 11 CD Checking Disabled [RFC4035][RFC6840][RFC Errata 4927]

EDNS Header Flags (16 bits)

Registration Procedure(s)
Standards Action
Available Formats

Bit Flag Description Reference
Bit 0 DO DNSSEC answer OK [RFC4035][RFC3225][RFC6840][RFC Errata 4928]
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

Child Synchronization (CSYNC) Flags

Registration Procedure(s)
Standards Action
Available Formats

Bit Flag Description Reference
0 immediate Immediately process this CSYNC record. [RFC7477, Section 3]
1 soaminimum Require a SOA serial number greater than the one specified. [RFC7477, Section]
2-15 Unassigned

Underscored and Globally Scoped DNS Node Names

Registration Procedure(s)
Expert Review
Dave Crocker, Frederico A C Neves
Available Formats

RR Type _NODE NAME Reference
* _example [RFC-ietf-dnsop-attrleaf-16, Section 4.5]
NULL _ta-* [2] [RFC8145]
OPENPGPKEY _openpgpkey [RFC7929]
SMIMEA _smimecert [RFC8162]
SRV _dccp [RFC2782]
SRV _http [RFC4386]
SRV _ipv6 [RFC5026]
SRV _ldap [RFC4386]
SRV _ocsp [RFC4386]
SRV _sctp [RFC2782]
SRV _sip [RFC5509]
SRV _tcp [RFC2782]
SRV _udp [RFC2782]
SRV _xmpp [RFC3921]
TLSA _dane [RFC7671]
TLSA _sctp [RFC6698]
TLSA _tcp [RFC6698]
TLSA _udp [RFC6698]
TXT _acme-challenge [draft-ietf-acme-acme]
TXT _dmarc [RFC7489]
TXT _domainkey [RFC6376]
TXT _mta-sts [draft-ietf-uta-mta-sts]
TXT _spf [RFC7208]
TXT _sztp [RFC-ietf-netconf-zerotouch-29]
TXT _tcp [RFC6763]
TXT _udp [RFC6763]
TXT _vouch [RFC5518]
URI _acct [RFC6118]
URI _dccp [RFC7566]
URI _email [RFC6118]
URI _ems [RFC6118]
URI _fax [RFC6118]
URI _ft [RFC6118]
URI _h323 [RFC6118]
URI _iax [RFC6118]
URI _ical-access [RFC6118]
URI _ical-sched [RFC6118]
URI _ifax [RFC6118]
URI _im [RFC6118]
URI _mms [RFC6118]
URI _pres [RFC6118]
URI _pstn [RFC6118]
URI _sctp [RFC6118]
URI _sip [RFC6118]
URI _sms [RFC6118]
URI _tcp [RFC6118]
URI _udp [RFC6118]
URI _unifmsg [RFC6118]
URI _vcard [RFC6118]
URI _videomsg [RFC6118]
URI _voice [RFC6118]
URI _voicemsg [RFC6118]
URI _vpim [RFC6118]
URI _web [RFC6118]
URI _xmpp [RFC6118]

DSO Type Codes

Ted Lemon, Sara Dickinson, John Dickinson
Available Formats

Range Registration Procedures
0x0004-0x003F Standards Action
0x0040-0xF7FF Expert Review
0xFC00-0xFFFF Standards Action
Type Name Early Data Status Reference
0x0000 Reserved NO Standards Track [RFC8490]
0x0001 KeepAlive OK Standards Track [RFC8490]
0x0002 RetryDelay NO Standards Track [RFC8490]
0x0003 EncryptionPadding NA Standards Track [RFC8490]
0x0004-0x003F Unassigned, reserved for DSO session-management TLVs NO
0x0040-0xF7FF Unassigned NO
0xF800-0xFBFF Reserved for Experimental/Local Use NO [RFC8490]
0xFC00-0xFFFF Reserved for future expansion NO


ID Name Contact URI Last Updated
[Brian_Hartvigsen] Brian Hartvigsen mailto:bhartvig& 2016-12-09
[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 Fältström mailto:paf& 2015-01-05
[Phillip_Hallam_Baker] Phillip Hallam-Baker mailto:phill& 2011-04-07
[Sam_Weiler] Sam Weiler mailto:weiler+iana& 2005-12
[Wolfgang_Riedel] Wolfgang Riedel mailto:wolfgang& 2016-02-26
[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 

NB      32      NetBIOS general Name Service
From [RFC-ietf-dnsop-attrleaf-16, Section 4.4]:
Under the NULL RR, the entry "_ta-*" denotes all node names beginning
with the string "_ta-*". It does NOT refer to a DNS wildcard