Skip to content

RR.md

Latest commit

 

History

History
977 lines (687 loc) · 32.8 KB

RR.md

File metadata and controls

977 lines (687 loc) · 32.8 KB

DNS Resource Record Support

This document describes every DNS resource record type known to the NetDNS2 library, organized into three sections:

  1. Supported Resource Records — fully implemented with wire-format encode/decode, zone-file text parse/format, and PHP class.
  2. Meta / Pseudo-types — types that appear in DNS packets but are not stored resource records (EDNS, zone-transfer control, transaction security, query wildcards).
  3. Unsupported Resource Records — types that appear in the IANA registry but are not implemented, with an explanation for each.

Supported Resource Records

A — IPv4 Address

Field Value
Type 1
RFC RFC 1035
Class \NetDNS2\RR\A

Maps a hostname to a 32-bit IPv4 address. The most common record type in the DNS.

Key fields: address (\NetDNS2\Data\IPv4)

NS — Name Server

Field Value
Type 2
RFC RFC 1035
Class \NetDNS2\RR\NS

Delegates a DNS zone to use the given authoritative name server.

Key fields: nsdname (\NetDNS2\Data\Domain)

CNAME — Canonical Name

Field Value
Type 5
RFC RFC 1035
Class \NetDNS2\RR\CNAME

Creates an alias from one domain name to another (the canonical name). Resolvers follow CNAME chains automatically.

Key fields: cname (\NetDNS2\Data\Domain)

SOA — Start of Authority

Field Value
Type 6
RFC RFC 1035
Class \NetDNS2\RR\SOA

Marks the beginning of a DNS zone and carries administrative parameters used for zone transfers and negative caching.

Key fields: mname (primary NS), rname (admin mailbox), serial, refresh, retry, expire, minimum

NULL — Null Record

Field Value
Type 10
RFC RFC 1035
Class \NetDNS2\RR\RR_NULL

Can hold any binary data up to 65,535 bytes. Used experimentally and for testing. The PHP class is named RR_NULL (not NULL) to avoid a conflict with the PHP reserved word.

Key fields: data (raw binary string)

WKS — Well-Known Services

Field Value
Type 11
RFC RFC 1035
Class \NetDNS2\RR\WKS

Describes the well-known IP services (TCP/UDP port numbers) that a host provides. Largely superseded by SRV records in modern deployments.

Key fields: address (IPv4), protocol (IP protocol number), bitmap (port bitmap)

PTR — Pointer

Field Value
Type 12
RFC RFC 1035
Class \NetDNS2\RR\PTR

Maps an IP address to a hostname (reverse DNS lookup). Used in in-addr.arpa (IPv4) and ip6.arpa (IPv6) zones.

Key fields: ptrdname (\NetDNS2\Data\Domain)

HINFO — Host Information

Field Value
Type 13
RFC RFC 1035
Class \NetDNS2\RR\HINFO

Describes the CPU and operating system of a host. Rarely published publicly due to security concerns; still used in some private/internal zones.

Key fields: cpu, os (character-string pairs)

MX — Mail Exchanger

Field Value
Type 15
RFC RFC 1035
Class \NetDNS2\RR\MX

Specifies the mail server responsible for accepting email for a domain. Multiple records with different preference values allow fallback.

Key fields: preference (priority, lower = preferred), exchange (\NetDNS2\Data\Domain)

TXT — Text

Field Value
Type 16
RFC RFC 1035
Class \NetDNS2\RR\TXT

Holds one or more arbitrary text strings. Widely used for domain ownership verification, SPF policies, DKIM public keys, and many other purposes.

Key fields: text (array of character strings, each up to 255 bytes)

RP — Responsible Person

Field Value
Type 17
RFC RFC 1183
Class \NetDNS2\RR\RP

Identifies the person responsible for a host, with an optional pointer to a TXT record containing contact details.

Key fields: mbox (mailbox domain), txtdname (TXT record name)

AFSDB — AFS Database Location

Field Value
Type 18
RFC RFC 1183
Class \NetDNS2\RR\AFSDB

Locates an AFS cell database server or a DCE/NCA cell directory server. Subtype 1 = AFS version 3 cell database server; subtype 2 = DCE authenticated name server.

Key fields: subtype (1 or 2), hostname (\NetDNS2\Data\Domain)

X25 — X.25 PSDN Address

Field Value
Type 19
RFC RFC 1183
Class \NetDNS2\RR\X25

Stores the X.25 Public Switched Data Network (PSDN) address for a host.

Key fields: address (PSDN address string)

ISDN — ISDN Address

Field Value
Type 20
RFC RFC 1183
Class \NetDNS2\RR\ISDN

Stores an ISDN telephone number and optional subaddress for a host.

Key fields: address (ISDN number), sa (optional subaddress)

RT — Route Through

Field Value
Type 21
RFC RFC 1183
Class \NetDNS2\RR\RT

Specifies an intermediate host for routing to destinations that use non-standard addresses (e.g., X.25, ISDN). Analogous to MX but for routing.

Key fields: preference, intermediate (\NetDNS2\Data\Domain)

SIG — Cryptographic Signature (legacy)

Field Value
Type 24
RFC RFC 2535
Class \NetDNS2\RR\SIG

The original DNSSEC signature record from RFC 2535. Now superseded by RRSIG (type 46), but still used for SIG(0) transaction authentication on DNS UPDATE messages. The library uses SIG for signing dynamic updates.

Key fields: typecovered, algorithm, labels, origttl, sigexp, sigincep, keytag, signname, signature

KEY — Public Key (legacy)

Field Value
Type 25
RFC RFC 2535, RFC 2930
Class \NetDNS2\RR\KEY

The original DNSSEC public key record from RFC 2535, superseded by DNSKEY (type 48). Still used for TKEY key exchange.

Key fields: flags, protocol, algorithm, key

PX — X.400/RFC 822 Mail Mapping

Field Value
Type 26
RFC RFC 2163
Class \NetDNS2\RR\PX

Maps between RFC 822 (internet) email addresses and X.400 email addresses for gateways.

Key fields: preference, map822 (RFC 822 domain), mapx400 (X.400 OR-address domain)

GPOS — Geographical Position

Field Value
Type 27
RFC RFC 1712
Class \NetDNS2\RR\GPOS

Specifies the geographical position of a host using longitude, latitude, and altitude strings. Superseded by LOC (type 29).

Key fields: longitude, latitude, altitude

AAAA — IPv6 Address

Field Value
Type 28
RFC RFC 3596
Class \NetDNS2\RR\AAAA

Maps a hostname to a 128-bit IPv6 address. The IPv6 equivalent of the A record.

Key fields: address (\NetDNS2\Data\IPv6)

LOC — Location Information

Field Value
Type 29
RFC RFC 1876
Class \NetDNS2\RR\LOC

Stores the geographic location (latitude, longitude, altitude, size, horizontal and vertical precision) of an internet resource.

Key fields: latitude, longitude, altitude, size, horiz_pre, vert_pre

EID — Endpoint Identifier

Field Value
Type 31
RFC Patton 1995
Class \NetDNS2\RR\EID

Used in the Nimrod routing architecture to store endpoint identifiers. Rarely seen in production.

Key fields: endpoint (binary hex string)

NIMLOC — Nimrod Locator

Field Value
Type 32
RFC Patton 1995
Class \NetDNS2\RR\NIMLOC

Used in the Nimrod routing architecture to store locators. Rarely seen in production.

Key fields: locator (binary hex string)

SRV — Service Location

Field Value
Type 33
RFC RFC 2782
Class \NetDNS2\RR\SRV

Specifies the hostname and port for a service. Allows services to be discovered without hard-coding port numbers. Widely used for SIP, XMPP, and many other protocols.

Key fields: priority, weight, port, target (\NetDNS2\Data\Domain)

NAPTR — Naming Authority Pointer

Field Value
Type 35
RFC RFC 2915
Class \NetDNS2\RR\NAPTR

Provides regular-expression-based rewriting of domain names and URIs. Used in ENUM (telephone-number-to-URI mapping) and for service discovery in VoIP.

Key fields: order, preference, flags, services, regexp, replacement

KX — Key Exchanger

Field Value
Type 36
RFC RFC 2230
Class \NetDNS2\RR\KX

Identifies hosts willing to act as key exchange intermediaries for a domain, analogous to MX for mail. Used with DNSSEC in some architectures.

Key fields: preference, exchanger (\NetDNS2\Data\Domain)

CERT — Certificate

Field Value
Type 37
RFC RFC 4398
Class \NetDNS2\RR\CERT

Stores a certificate (X.509, PGP, SPKI, etc.) or a certificate revocation list (CRL) in the DNS.

Key fields: format, key_tag, algorithm, certificate (base64)

DNAME — Delegation Name

Field Value
Type 39
RFC RFC 2672
Class \NetDNS2\RR\DNAME

Redirects an entire subtree of the DNS namespace (unlike CNAME, which only redirects a single name). Often used for IPv6 reverse-lookup zones or domain mergers.

Key fields: target (\NetDNS2\Data\Domain)

OPT — EDNS Options

Field Value
Type 41
RFC RFC 2671 / RFC 6891
Class \NetDNS2\RR\OPT

A pseudo-RR (meta-type) that carries EDNS(0) options in the additional section of a DNS message. Not a real resource record — used only for protocol extension signalling. The library supports the following EDNS option sub-types:

Option Code RFC
NSID 3 RFC 5001
DAU 5 RFC 6975
DHU 6 RFC 6975
N3U 7 RFC 6975
ECS (Client Subnet) 8 RFC 7871
EXPIRE 9 RFC 7314
COOKIE 10 RFC 7873
KEEPALIVE (TCP Keepalive) 11 RFC 7828
PADDING 12 RFC 7830
CHAIN 13 RFC 7901
KEYTAG 14 RFC 8145
UMBRELLA 20292 Cisco-internal
ZONEVERSION 19 RFC 9660

APL — Address Prefix List

Field Value
Type 42
RFC RFC 3123
Class \NetDNS2\RR\APL

Stores a list of address prefixes (IPv4 and/or IPv6) with optional negation. Used for Access Control Lists (ACLs) in DNS-based configurations.

Key fields: apl_items (array of prefix entries, each with address family, prefix length, negation flag, and address)

DS — Delegation Signer

Field Value
Type 43
RFC RFC 4034
Class \NetDNS2\RR\DS

Contains a hash of a DNSKEY record in a child zone, creating the chain of trust in DNSSEC. Published in the parent zone to authenticate the child zone's key.

Key fields: keytag, algorithm, digesttype, digest

SSHFP — SSH Public Key Fingerprint

Field Value
Type 44
RFC RFC 4255
Class \NetDNS2\RR\SSHFP

Stores the fingerprint of an SSH server's public key in DNS, enabling clients to verify host keys without manual intervention (used with DNSSEC).

Key fields: algorithm (key type: RSA, DSS, ECDSA, ED25519, etc.), fingerprint_type (SHA-1 or SHA-256), fingerprint

IPSECKEY — IPsec Key

Field Value
Type 45
RFC RFC 4025
Class \NetDNS2\RR\IPSECKEY

Stores a public key for use with IPsec, allowing hosts to discover IPsec keying material via DNS.

Key fields: precedence, gateway_type, algorithm, gateway (IPv4/IPv6/domain), key (base64)

RRSIG — Resource Record Set Signature

Field Value
Type 46
RFC RFC 4034
Class \NetDNS2\RR\RRSIG

The DNSSEC cryptographic signature for an RRset. Replaces the older SIG record (type 24) for signing zone data.

Key fields: typecovered, algorithm, labels, origttl, sigexp, sigincep, keytag, signname, signature

NSEC — Next Secure

Field Value
Type 47
RFC RFC 4034
Class \NetDNS2\RR\NSEC

Used in DNSSEC to provide authenticated denial of existence. Links the signed zone's resource records in canonical order and identifies which record types exist at the owner name.

Key fields: next (next owner name), types (array of type mnemonics)

DNSKEY — DNS Public Key

Field Value
Type 48
RFC RFC 4034
Class \NetDNS2\RR\DNSKEY

Holds the public key used in DNSSEC to verify RRSIG signatures. Zone signing keys (ZSK) and key signing keys (KSK) are both stored as DNSKEY records.

Key fields: flags (Zone Key flag, SEP bit), protocol (must be 3), algorithm, key (base64)

DHCID — DHCP Identifier

Field Value
Type 49
RFC RFC 4701
Class \NetDNS2\RR\DHCID

Used in the DHCP/DNS interaction protocol to associate a DHCP client with its DNS records, preventing unauthorized updates.

Key fields: id (base64-encoded identifier)

NSEC3 — Next Secure v3

Field Value
Type 50
RFC RFC 5155
Class \NetDNS2\RR\NSEC3

An improvement over NSEC that uses hashed owner names to prevent zone enumeration while still providing authenticated denial of existence.

Key fields: algorithm, flags, iterations, salt, hnxt (hashed next owner name), types

NSEC3PARAM — NSEC3 Parameters

Field Value
Type 51
RFC RFC 5155
Class \NetDNS2\RR\NSEC3PARAM

Published at the zone apex to indicate the NSEC3 hashing parameters (algorithm, flags, iterations, salt) used in the zone.

Key fields: algorithm, flags, iterations, salt

TLSA — TLS Authentication

Field Value
Type 52
RFC RFC 6698
Class \NetDNS2\RR\TLSA

Associates a TLS server certificate with a domain name (DANE — DNS-based Authentication of Named Entities), allowing clients to verify TLS certificates via DNSSEC rather than traditional CAs.

Key fields: cert_usage, selector, matching_type, certificate (hex)

SMIMEA — S/MIME Certificate Association

Field Value
Type 53
RFC RFC 8162
Class \NetDNS2\RR\SMIMEA

Associates an S/MIME certificate with an email address via DNS (using DANE), enabling secure email clients to discover encryption certificates automatically.

Key fields: cert_usage, selector, matching_type, certificate (hex)

HIP — Host Identity Protocol

Field Value
Type 55
RFC RFC 5205
Class \NetDNS2\RR\HIP

Stores HIP parameters: a public key and optionally a list of rendezvous servers, separating the identity of a host from its location (IP address).

Key fields: hit (host identity tag), algorithm, public_key (base64), rendezvous_servers (array of domains)

TALINK — Trust Anchor Link

Field Value
Type 58
RFC —
Class \NetDNS2\RR\TALINK

Used by DNSSEC trust anchor management to link trust anchors. Part of a mechanism for automated trust anchor updates.

Key fields: previous (domain), next (domain)

CDS — Child DS

Field Value
Type 59
RFC RFC 7344
Class \NetDNS2\RR\CDS

Published in a child zone to signal the desired DS record content in the parent zone. Enables automated DNSSEC delegation trust management. Identical wire format to DS.

Key fields: keytag, algorithm, digesttype, digest

CDNSKEY — Child DNSKEY

Field Value
Type 60
RFC RFC 7344
Class \NetDNS2\RR\CDNSKEY

Published in a child zone to indicate the DNSKEY that the parent should use when constructing a DS record. Companion to CDS. Identical wire format to DNSKEY.

Key fields: flags, protocol, algorithm, key (base64)

OPENPGPKEY — OpenPGP Public Key

Field Value
Type 61
RFC RFC 7929
Class \NetDNS2\RR\OPENPGPKEY

Stores an OpenPGP public key in the DNS, allowing email clients to discover encryption keys automatically for a given email address.

Key fields: key (base64-encoded transferable public key packet)

CSYNC — Child-to-Parent Synchronization

Field Value
Type 62
RFC RFC 7477
Class \NetDNS2\RR\CSYNC

Allows a child zone to request that the parent zone synchronize specific record types (e.g., NS glue, A/AAAA records) automatically.

Key fields: serial, flags, types (array of type mnemonics)

ZONEMD — Zone Message Digest

Field Value
Type 63
RFC RFC 8976
Class \NetDNS2\RR\ZONEMD

Contains a cryptographic digest of the entire zone's contents, allowing recipients of zone files to verify zone integrity.

Key fields: serial, scheme, algorithm, digest (hex)

SVCB — Service Binding

Field Value
Type 64
RFC RFC 9460
Class \NetDNS2\RR\SVCB

Provides connection endpoints and associated parameters for internet services, enabling clients to connect more efficiently (e.g., via ALPN negotiation, ECH, IP hints). The HTTPS record type (65) is a variant.

Key fields: priority (0 = alias mode), target (domain), params (array of SvcParams: alpn, port, ipv4hint, ipv6hint, ech, mandatory, etc.)

HTTPS — HTTPS Service Binding

Field Value
Type 65
RFC RFC 9460
Class \NetDNS2\RR\HTTPS

An SVCB-compatible record specifically for HTTPS services. Allows browsers and clients to discover HTTPS connection parameters (ALPN, ECH keys, IP hints) via DNS before connecting. Subclasses SVCB.

Key fields: Same as SVCB

DSYNC — Generalized Notify

Field Value
Type 66
RFC draft-ietf-dnsop-generalized-notify
Class \NetDNS2\RR\DSYNC

Provides a mechanism for generalizing DNS NOTIFY messages to support delegation management operations (CSYNC, CDS/CDNSKEY updates) beyond zone transfers.

Key fields: type (covered type), scheme, port, target (domain)

HHIT — HIP Intermediary Discovery (HIT)

Field Value
Type 67
RFC RFC 9886
Class \NetDNS2\RR\HHIT

Part of the HIP (Host Identity Protocol) Intermediary Discovery mechanism. Stores a HIT (Host Identity Tag) for a HIP intermediary.

Key fields: hit_suite_id, hit (hex)

BRID — HIP Intermediary Discovery (Rendezvous)

Field Value
Type 68
RFC RFC 9886
Class \NetDNS2\RR\BRID

Part of the HIP (Host Identity Protocol) Intermediary Discovery mechanism. Stores the rendezvous server address for a HIP relay.

Key fields: hit_suite_id, hit (hex)

SPF — Sender Policy Framework

Field Value
Type 99
RFC RFC 4408
Class \NetDNS2\RR\SPF

Originally a dedicated record type for SPF email authentication policies. Superseded by TXT records (RFC 7208 removed SPF as a record type); both types carry the same v=spf1 … string. SPF type is still encountered in older zones.

Key fields: text (same format as TXT)

NID — Node Identifier

Field Value
Type 104
RFC RFC 6742
Class \NetDNS2\RR\NID

Part of the ILNP (Identifier-Locator Network Protocol) suite. Stores a 64-bit node identifier for a network node.

Key fields: preference, node_id (64-bit identifier in colon-separated hex)

L32 — 32-bit Locator

Field Value
Type 105
RFC RFC 6742
Class \NetDNS2\RR\L32

Part of the ILNP suite. Stores a 32-bit locator (IPv4-style) identifying a network attachment point.

Key fields: preference, locator (dotted-decimal IPv4 notation)

L64 — 64-bit Locator

Field Value
Type 106
RFC RFC 6742
Class \NetDNS2\RR\L64

Part of the ILNP suite. Stores a 64-bit locator (IPv6-prefix-style) identifying a network attachment point.

Key fields: preference, locator (colon-separated hex)

LP — Locator Pointer

Field Value
Type 107
RFC RFC 6742
Class \NetDNS2\RR\LP

Part of the ILNP suite. Points to a domain name that holds L32 or L64 records, allowing indirection in ILNP locator lookups.

Key fields: preference, target (\NetDNS2\Data\Domain)

EUI48 — 48-bit EUI (MAC-48)

Field Value
Type 108
RFC RFC 7043
Class \NetDNS2\RR\EUI48

Stores a 48-bit IEEE EUI (Ethernet MAC address) in the DNS. Intended for specific use cases such as DHCP-DNS mapping; not for general publication.

Key fields: address (colon-separated hex, e.g., 00:11:22:33:44:55)

EUI64 — 64-bit EUI

Field Value
Type 109
RFC RFC 7043
Class \NetDNS2\RR\EUI64

Stores a 64-bit IEEE EUI address in the DNS. Same purpose as EUI48 but for 64-bit identifiers.

Key fields: address (colon-separated hex, e.g., 00:11:22:33:44:55:66:77)

URI — Uniform Resource Identifier

Field Value
Type 256
RFC RFC 7553
Class \NetDNS2\RR\URI

Maps a hostname (or _service._proto.hostname) to a target URI. Allows DNS-based discovery of services via full URIs.

Key fields: priority, weight, target (URI string)

CAA — Certification Authority Authorization

Field Value
Type 257
RFC RFC 8659
Class \NetDNS2\RR\CAA

Restricts which certificate authorities (CAs) are authorized to issue TLS certificates for a domain. CAs must check CAA records before issuance.

Key fields: flags, tag (issue, issuewild, iodef), value

AVC — Application Visibility and Control

Field Value
Type 258
RFC — (Cisco proprietary)
Class \NetDNS2\RR\AVC

A Cisco-specific record type used in Application Visibility and Control deployments. Carries text strings similar to TXT records.

Key fields: text (array of strings)

AMTRELAY — Automatic Multicast Tunneling Relay

Field Value
Type 260
RFC RFC 8777
Class \NetDNS2\RR\AMTRELAY

Discovers AMT (Automatic Multicast Tunneling) relay addresses via DNS. Clients use AMTRELAY records to find the appropriate AMT relay for a multicast source.

Key fields: precedence, discovery_optional (flag), relay_type, relay (IPv4/IPv6/domain)

RESINFO — Resolver Information

Field Value
Type 261
RFC RFC 9606
Class \NetDNS2\RR\RESINFO

Published by a DNS resolver to communicate its capabilities and configuration to clients. Uses the same key=value SvcParam format as SVCB.

Key fields: SvcParam key-value pairs (e.g., qnamemin, exterr, infourl)

TA — DNSSEC Trust Authority

Field Value
Type 32768
RFC —
Class \NetDNS2\RR\TA

Used in the DNSSEC Lookaside Validation (DLV) alternative trust hierarchy. Same wire format as DS.

Key fields: keytag, algorithm, digesttype, digest

DLV — DNSSEC Lookaside Validation

Field Value
Type 32769
RFC RFC 4431
Class \NetDNS2\RR\DLV

Allows DNSSEC validation in zones whose parent zones do not publish DS records, using a separate lookaside validation tree. Now obsolete since the root zone is signed; the ISC DLV registry was shut down in 2017.

Key fields: keytag, algorithm, digesttype, digest

TYPE65534 — Private BIND Record

Field Value
Type 65534
RFC —
Class \NetDNS2\RR\TYPE65534

An internal private record type used by BIND for its own purposes. Not an IANA-assigned type.

Key fields: data (raw binary)

Meta / Pseudo-types

These types appear in DNS packet headers or the additional section, but are not stored resource records — they carry protocol control information.

Type Number RFC Description
SIG0 0 RFC 2931 Transaction-level signature using SIG records. The library uses SIG(0) to sign DNS UPDATE messages. Handled via \NetDNS2\RR\SIG.
OPT 41 RFC 6891 EDNS(0) options container — carried in the additional section, not stored in zone data. See the OPT entry above for the full list of supported EDNS options.
TKEY 249 RFC 2930 Transaction key establishment for TSIG. Used to negotiate shared secrets for subsequent TSIG-signed requests.
TSIG 250 RFC 2845 Transaction signature. Signs individual DNS messages using a pre-shared HMAC secret. Supported algorithms: HMAC-MD5, HMAC-SHA1, HMAC-SHA224, HMAC-SHA256, HMAC-SHA384, HMAC-SHA512.
IXFR 251 RFC 1995 Incremental zone transfer. Only full-zone (AXFR-style) responses to IXFR queries are currently supported.
AXFR 252 RFC 1035 Full zone transfer. Fully supported; the library can initiate and receive AXFR responses, optionally authenticated with TSIG or SIG(0).
ANY 255 RFC 1035 Wildcard query type requesting all record types for a name. Supported as a query type; handled via \NetDNS2\RR\ANY.

Unsupported Resource Records

The following types are registered in the IANA DNS Parameters registry but are not implemented in NetDNS2. The reason for each omission is given below.

Obsolete types — retired in RFC 1035 itself or replaced early

Type Number RFC Reason
MD 3 RFC 1035 Obsolete. "Mail Destination" — superseded by MX before DNS was widely deployed. RFC 1035 itself marks it obsolete.
MF 4 RFC 1035 Obsolete. "Mail Forwarder" — superseded by MX at the same time as MD. RFC 1035 marks it obsolete.
MB 7 RFC 1035 Obsolete. Experimental mailbox record that was never standardized or deployed in practice.
MG 8 RFC 1035 Obsolete. Experimental mail group record; same story as MB.
MR 9 RFC 1035 Obsolete. Experimental mail rename record; same story as MB.
MINFO 14 RFC 1035 Obsolete. Mailbox/mail list information; never widely deployed and officially obsolete.

Deprecated types — superseded by better alternatives

Type Number RFC Reason
NSAP 22 RFC 1706 Deprecated. OSI NSAP (Network Service Access Point) addresses; OSI networking never achieved widespread internet adoption.
NSAP-PTR 23 RFC 1348 Deprecated. Reverse-mapping for NSAP addresses; superseded along with NSAP.
NXT 30 RFC 2065 Obsolete. The original DNSSEC "Next" record for authenticated denial of existence, replaced by NSEC (type 47) in RFC 3755.
ATMA 34 — Removed from the IANA registry. ATM (Asynchronous Transfer Mode) networking was never widely integrated with DNS.
A6 38 RFC 2874 Experimental. An alternative IPv6 address record with complex chain-following semantics; downgraded to experimental status by RFC 3363 and superseded entirely by AAAA (type 28).
GPOS 27 RFC 1712 Superseded by LOC (type 29). GPOS is still implemented in this library for completeness but LOC is preferred.
SPF 99 RFC 4408 Functionally replaced by TXT. RFC 7208 removed SPF as a distinct record type; all SPF policies are now published in TXT records. The SPF type is still implemented in this library to handle legacy zones.
MAILB 253 RFC 883 Obsolete. A meta-query for MB, MG, and MR records — none of which are deployed.
MAILA 254 RFC 973 Obsolete. A meta-query for MD and MF records — none of which are deployed.

Types without a published RFC or stable specification

Type Number Reference Reason
SINK 40 Internet-Draft An Internet-Draft to store arbitrary "kitchen sink" data was proposed but never published as an RFC.
NINFO 56 Internet-Draft A proposed record for zone status information; the draft expired and was never standardized.
RKEY 57 Internet-Draft A proposed resource record for additional DNSSEC keying material; the draft was abandoned.
UINFO 100 — No RFC. An internal BIND extension for storing user information; not an IANA standard.
UID 101 — No RFC. An internal BIND extension for user IDs; not an IANA standard.
GID 102 — No RFC. An internal BIND extension for group IDs; not an IANA standard.
UNSPEC 103 — No RFC. An internal BIND extension for unspecified data; not an IANA standard.
DOA 259 Internet-Draft "DNS-based Objects and Attributes" — the draft (draft-durand-doa-over-dns) has not been standardized.
WALLET 262 Internet-Draft A proposed record for cryptocurrency wallet addresses; not yet standardized.
CLA 263 Internet-Draft Not yet standardized.
IPN 264 Internet-Draft Not yet standardized.

Partially supported / planned

Type Number RFC Status
IXFR 251 RFC 1995 Only full-zone (AXFR-style) responses are supported. True incremental transfer parsing (delta sections) is not yet implemented.
NXNAME 128 Internet-Draft Reserved for a new authenticated NXDOMAIN response type; not yet standardized or implemented.