DNS Resource Record Support

February 26, 2026 · View on GitHub

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

Supported Resource Records — fully implemented with wire-format encode/decode, zone-file text parse/format, and PHP class.
Meta / Pseudo-types — types that appear in DNS packets but are not stored resource records (EDNS, zone-transfer control, transaction security, query wildcards).
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 Largely superseded by SRV records in modern deployments.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.