DNS RR代码和含义

记录类型

代码	号码	定义的 RFC	描述	功能
A	1	RFC 1035	IP 地址记录	传回一个 32 比特的 IPv4 地址，最常用于映射主机名称到 IP地址，但也用于DNSBL（RFC 1101）等。
AAAA	28	RFC 3596	IPv6 IP 地址记录	传回一个 128 比特的 IPv6 地址，最常用于映射主机名称到 IP 地址。
AFSDB	18	RFC 1183	AFS文件系统	（Andrew File System）数据库核心的位置，于域名以外的 AFS 客户端常用来联系 AFS 核心。这个记录的子类型是被过时的的 DCE/DFS（DCE Distributed File System）所使用。
APL	42	RFC 3123	地址前缀列表	指定地址列表的范围，例如：CIDR 格式为各个类型的地址（试验性）。
CAA	257	RFC 6844	权威认证授权	DNS认证机构授权，限制主机/域的可接受的CA
CDNSKEY	60	RFC 7344	子关键记录	关键记录记录的子版本，用于转移到父级
CDS	59	RFC 7344	子委托签发者	委托签发者记录的子版本，用于转移到父级
CERT	37	RFC 4398	证书记录	存储 PKIX、SPKI、PGP等。
CNAME	5	RFC 1035	规范名称记录	一个主机名字的别名：域名系统将会继续尝试查找新的名字。
DHCID	49	RFC 4701	DHCP（动态主机设置协议）识别码	用于将 FQDN 选项结合至 DHCP。
DLV	32769	RFC 4431	DNSSEC（域名系统安全扩展）来源验证记录	为不在DNS委托者内发布DNSSEC的信任锚点，与 DS 记录使用相同的格式，RFC 5074 介绍了如何使用这些记录。
DNAME	39	RFC 2672	代表名称	DNAME 会为名称和其子名称产生别名，与 CNAME 不同，在其标签别名不会重复。但与 CNAME 记录相同的是，DNS将会继续尝试查找新的名字。
DNSKEY	48	RFC 4034	DNS 关键记录	于DNSSEC内使用的关键记录，与 KEY 使用相同格式。
DS	43	RFC 4034	委托签发者	此记录用于鉴定DNSSEC已授权区域的签名密钥。
HIP	55	RFC 5205	主机鉴定协议	将端点标识符及IP 地址定位的分开的方法。
IPSECKEY	45	RFC 4025	IPSEC 密钥	与 IPSEC 同时使用的密钥记录。
KEY	25	RFC 2535[1]RFC 2930[2]	关键记录	只用于 SIG(0)（RFC 2931）及 TKEY（RFC 2930）。[3]RFC 3455 否定其作为应用程序键及限制DNSSEC的使用。[4]RFC 3755 指定了 DNSKEY 作为DNSSEC的代替。[5]
LOC记录（LOC record）	29	RFC 1876	位置记录	将一个域名指定地理位置。
MX记录（MX record）	15	RFC 1035	电邮交互记录	引导域名到该域名的邮件传输代理（MTA, Message Transfer Agents）列表。
NAPTR记录（NAPTR record）	35	RFC 3403	命名管理指针	允许基于正则表达式的域名重写使其能够作为 URI、进一步域名查找等。
NS	2	RFC 1035	名称服务器记录	委托DNS区域（DNS zone）使用已提供的权威域名服务器。
NSEC	47	RFC 4034	下一代安全记录	DNSSEC 的一部分 — 用来验证一个未存在的服务器，使用与 NXT（已过时）记录的格式。
NSEC3	50	RFC 5155	NSEC 记录第三版	用作允许未经允许的区域行走以证明名称不存在性的 DNSSEC 扩展。
NSEC3PARAM	51	RFC 5155	NSEC3 参数	与 NSEC3 同时使用的参数记录。
OPENPGPKEY	61	RFC 7929	OpenPGP公钥记录	基于DNS的域名实体认证方法，用于使用OPENPGPKEY DNS资源记录在特定电子邮件地址的DNS中发布和定位OpenPGP公钥。
PTR	12	RFC 1035	指针记录	引导至一个规范名称（Canonical Name）。与 CNAME 记录不同，DNS“不会”进行进程，只会传回名称。最常用来运行反向 DNS 查找，其他用途包括引作 DNS-SD。
RRSIG	46	RFC 4034	DNSSEC 证书	DNSSEC 安全记录集证书，与 SIG 记录使用相同的格式。
RP	17	RFC 1183	负责人	有关域名负责人的信息，电邮地址的 @ 通常写为 a。
SIG	24	RFC 2535	证书	SIG(0)（RFC 2931）及 TKEY（RFC 2930）使用的证书。[5]RFC 3755 designated RRSIG as the replacement for SIG for use within DNSSEC.[5]
SOA	6	RFC 1035	权威记录的起始	指定有关DNS区域的权威性信息，包含主要名称服务器、域名管理员的电邮地址、域名的流水式编号、和几个有关刷新区域的定时器。
SPF	99	RFC 4408	SPF 记录	作为 SPF 协议的一部分，优先作为先前在 TXT 存储 SPF 数据的临时做法，使用与先前在 TXT 存储的格式。
SRV记录（SRV record）	33	RFC 2782	服务定位器	广义为服务定位记录，被新式协议使用而避免产生特定协议的记录，例如：MX 记录。
SSHFP	44	RFC 4255	SSH 公共密钥指纹	DNS 系统用来发布 SSH 公共密钥指纹的资源记录，以用作辅助验证服务器的真实性。
TA	32768	无	DNSSEC 信任当局	DNSSEC 一部分无签订 DNS 根目录的部署提案，，使用与 DS 记录相同的格式[6][7]。
TKEY记录（TKEY record）	249	RFC 2930	秘密密钥记录	为TSIG提供密钥材料的其中一类方法，that is 在公共密钥下加密的 accompanying KEY RR。[8]
TSIG	250	RFC 2845	交易证书	用以认证动态更新（Dynamic DNS）是来自合法的客户端，或与 DNSSEC 一样是验证回应是否来自合法的递归名称服务器。[9]
TXT	16	RFC 1035	文本记录	最初是为任意可读的文本 DNS 记录。自1990年起，些记录更经常地带有机读数据，以 RFC 1464 指定：机会性加密（opportunistic encryption）、Sender Policy Framework（虽然这个临时使用的 TXT 记录在 SPF 记录推出后不被推荐）、DomainKeys、DNS-SD等。
URI	256	RFC 7553	统一资源标识符	可用于发布从主机名到URI的映射。

其他类型及伪资源记录

其他类型的资源记录简单地提供一些类型的消息（如：HINFO 记录提供电脑或操作系统的类型），或传回实验中之功能的数据。“type”字段也使用于其他协议作各种操作。

代码	号码	定义的 RFC	描述	功能
*	255	RFC 1035	所有缓存的记录	传回所有服务器已知类型的记录。如果服务器未有任何关于名称的记录，该请求将被转发。而传回的记录未必完全完成，例如：当一个名称有 A 及 MX 类型的记录时，但服务器已缓存了 A 记录，就只有 A 记录会被传回。
AXFR	252	RFC 1035	全域转移	由主域名服务器转移整个区域文件至二级域名服务器。
IXFR	251	RFC 1995	增量区域转移	请求只有与先前流水式编号不同的特定区域的区域转移。此请求有机会被拒绝，如果权威服务器由于配置或缺乏必要的数据而无法履行请求，一个完整的（AXFR）会被发送以作回应。
OPT	41	RFC 2671	选项	这是一个“伪 DNS记录类型”以支持 EDNS。

过时的记录类型

发展呈现废弃一些最初定义的记录类型。从 IANA 的记录可见，一些记录类型由于一些原因而被限制其使用、一些被标示为明显过时的、有些是为了隐藏的服务、有些是为了旧版本的服务、有的有特别记录指出它们是“不正确的”。

• 由 RFC 973 定义为过时：MD(3)、MF (4)、MAILA (254)
• 为了发布邮件列表订户的 DNS 记录：MB(7)、MG(8)、MR(9)、MINFO(14)、MAILB (253)。 在 RFC 883 标明的意图是为了让 MB 代替 SMTP VRFY 指令、MG 代替 SMTP EXPN 指令、及让 MR 代替“551 User Not Local”SMTP 错误。其后，RFC 2505 提议将 VRFY 及 EXPN 指令两者停用，使利用 MB 及 MG 永远不可能获得通过。
• 在 RFC 1123 不提议使用“not to be relied upon”（RFC 1127 有更多的信息）：WKS(11)^[10]
• 错误: NB(32)、NBSTAT(33)（自 RFC 1002）；号码现已分配给 NIMLOC 及 SRV。
• 由 RFC 1035 定义为过时：NULL(10)（RFC 883 定义“完成查询”（操作码二及可能是三）有在使用此记录，后来 RFC 1035 重新分配操作码二为“状态”及保留操作码三）。
• 定义为早期的 IPv6 但其后由 RFC 3363 降级为试验性：A6(38)
• 由 DNSSEC 更新（RFC 3755） 定义为过时：NXT(30)。同一时间，为 KEY 及 SIG 域名的适用性限制为不包括 DNSSEC。
• 第一版 DNSSEC（RFC 2230、RFC 2065）的一部分，现已过时：KX(36)
• 目前没有任何显著的应用程序使用：HINFO(13)、RP(17)、X25(19)、ISDN(20)、RT(21)、NSAP(22)、NSAP-PTR(23)、PX(26)、EID(31)、NIMLOC(32)、ATMA(34)、APL(42)
• 由 Kitchen Sink 互联网草案，但从未达至 RFC 水平：SINK(40)
• 一个 LOC 记录更有限的早期版本：GPOS(27)
• IANA 保留，及后未有 RFC 记录它们 [1] 而支持已由 BIND 于九零年初移除：UINFO(100), UID(101)、GID(102)、UNSPEC(103)

RP(17) 可能被使用于有关指定的主机的不同联系点、子网域其他 SOA 记录不包含的域名级别的人类可读信息。

From wiki :

Resource records

Type	Type id. (decimal)	Defining RFC	Description	Function
A	1	RFC 1035[1]	Address record	Returns a 32-bit IPv4 address, most commonly used to map hostnames to an IP address of the host, but it is also used for DNSBLs, storing subnet masks in RFC 1101, etc.
AAAA	28	RFC 3596[2]	IPv6 address record	Returns a 128-bit IPv6 address, most commonly used to map hostnames to an IP address of the host.
AFSDB	18	RFC 1183	AFS database record	Location of database servers of an AFS cell. This record is commonly used by AFS clients to contact AFS cells outside their local domain. A subtype of this record is used by the obsolete DCE/DFS file system.
APL	42	RFC 3123	Address Prefix List	Specify lists of address ranges, e.g. in CIDR format, for various address families. Experimental.
CAA	257	RFC 6844	Certification Authority Authorization	DNS Certification Authority Authorization, constraining acceptable CAs for a host/domain
CDNSKEY	60	RFC 7344	Child DNSKEY	Child copy of DNSKEY record, for transfer to parent
CDS	59	RFC 7344	Child DS	Child copy of DS record, for transfer to parent
CERT	37	RFC 4398	Certificate record	Stores PKIX, SPKI, PGP, etc.
CNAME	5	RFC 1035[1]	Canonical name record	Alias of one name to another: the DNS lookup will continue by retrying the lookup with the new name.
DHCID	49	RFC 4701	DHCP identifier	Used in conjunction with the FQDN option to DHCP
DLV	32769	RFC 4431	DNSSEC Lookaside Validation record	For publishing DNSSEC trust anchors outside of the DNS delegation chain. Uses the same format as the DS record. RFC 5074 describes a way of using these records.
DNAME	39	RFC 6672		Alias for a name and all its subnames, unlike CNAME, which is an alias for only the exact name. Like a CNAME record, the DNS lookup will continue by retrying the lookup with the new name.
DNSKEY	48	RFC 4034	DNS Key record	The key record used in DNSSEC. Uses the same format as the KEY record.
DS	43	RFC 4034	Delegation signer	The record used to identify the DNSSEC signing key of a delegated zone
HIP	55	RFC 8005	Host Identity Protocol	Method of separating the end-point identifier and locator roles of IP addresses.
IPSECKEY	45	RFC 4025	IPsec Key	Key record that can be used with IPsec
KEY	25	RFC 2535[3] and RFC 2930[4]	Key record	Used only for SIG(0) (RFC 2931) and TKEY (RFC 2930).[5] RFC 3445 eliminated their use for application keys and limited their use to DNSSEC.[6] RFC 3755 designates DNSKEY as the replacement within DNSSEC.[7] RFC 4025 designates IPSECKEY as the replacement for use with IPsec.[8]
KX	36	RFC 2230	Key Exchanger record	Used with some cryptographic systems (not including DNSSEC) to identify a key management agent for the associated domain-name. Note that this has nothing to do with DNS Security. It is Informational status, rather than being on the IETF standards-track. It has always had limited deployment, but is still in use.
LOC	29	RFC 1876	Location record	Specifies a geographical location associated with a domain name
MX	15	RFC 1035[1] and RFC 7505	Mail exchange record	Maps a domain name to a list of message transfer agents for that domain
NAPTR	35	RFC 3403	Naming Authority Pointer	Allows regular-expression-based rewriting of domain names which can then be used as URIs, further domain names to lookups, etc.
NS	2	RFC 1035[1]	Name server record	Delegates a DNS zone to use the given authoritative name servers
NSEC	47	RFC 4034	Next Secure record	Part of DNSSEC—used to prove a name does not exist. Uses the same format as the (obsolete) NXT record.
NSEC3	50	RFC 5155	Next Secure record version 3	An extension to DNSSEC that allows proof of nonexistence for a name without permitting zonewalking
NSEC3PARAM	51	RFC 5155	NSEC3 parameters	Parameter record for use with NSEC3
OPENPGPKEY	61	RFC 7929	OpenPGP public key record	A DNS-based Authentication of Named Entities (DANE) method for publishing and locating OpenPGP public keys in DNS for a specific email address using an OPENPGPKEY DNS resource record.
PTR	12	RFC 1035[1]	Pointer record	Pointer to a canonical name. Unlike a CNAME, DNS processing stops and just the name is returned. The most common use is for implementing reverse DNS lookups, but other uses include such things as DNS-SD.
RRSIG	46	RFC 4034	DNSSEC signature	Signature for a DNSSEC-secured record set. Uses the same format as the SIG record.
RP	17	RFC 1183	Responsible Person	Information about the responsible person(s) for the domain. Usually an email address with the @ replaced by a .
SIG	24	RFC 2535	Signature	Signature record used in SIG(0) (RFC 2931) and TKEY (RFC 2930).[7] RFC 3755 designated RRSIG as the replacement for SIG for use within DNSSEC.[7]
SOA	6	RFC 1035[1] and RFC 2308[9]	Start of [a zone of] authority record	Specifies authoritative information about a DNS zone, including the primary name server, the email of the domain administrator, the domain serial number, and several timers relating to refreshing the zone.
SRV	33	RFC 2782	Service locator	Generalized service location record, used for newer protocols instead of creating protocol-specific records such as MX.
SSHFP	44	RFC 4255	SSH Public Key Fingerprint	Resource record for publishing SSH public host key fingerprints in the DNS System, in order to aid in verifying the authenticity of the host. RFC 6594 defines ECC SSH keys and SHA-256 hashes. See the IANA SSHFP RR parameters registry for details.
TA	32768	N/A	DNSSEC Trust Authorities	Part of a deployment proposal for DNSSEC without a signed DNS root. See the IANA database and Weiler Spec for details. Uses the same format as the DS record.
TKEY	249	RFC 2930	Transaction Key record	A method of providing keying material to be used with TSIG that is encrypted under the public key in an accompanying KEY RR.[10]
TLSA	52	RFC 6698	TLSA certificate association	A record for DANE. RFC 6698 defines "The TLSA DNS resource record is used to associate a TLS server certificate or public key with the domain name where the record is found, thus forming a 'TLSA certificate association'".
TSIG	250	RFC 2845	Transaction Signature	Can be used to authenticate dynamic updates as coming from an approved client, or to authenticate responses as coming from an approved recursive name server[11] similar to DNSSEC.
TXT	16	RFC 1035[1]	Text record	Originally for arbitrary human-readable text in a DNS record. Since the early 1990s, however, this record more often carries machine-readable data, such as specified by RFC 1464, opportunistic encryption, Sender Policy Framework, DKIM, DMARC, DNS-SD, etc.
URI	256	RFC 7553	Uniform Resource Identifier	Can be used for publishing mappings from hostnames to URIs.

Other types and pseudo resource records

Other types of records simply provide some types of information (for example, an HINFO record gives a description of the type of computer/OS a host uses), or others return data used in experimental features. The "type" field is also used in the protocol for various operations.

Type	Type id.	Defining RFC	Description	Function
*	255	RFC 1035[1]	All cached records	Returns all records of all types known to the name server. If the name server does not have any information on the name, the request will be forwarded on. The records returned may not be complete. For example, if there is both an A and an MX for a name, but the name server has only the A record cached, only the A record will be returned. Sometimes referred to as "ANY", for example in Windows nslookup and Wireshark.
AXFR	252	RFC 1035[1]	Authoritative Zone Transfer	Transfer entire zone file from the master name server to secondary name servers.
IXFR	251	RFC 1996	Incremental Zone Transfer	Requests a zone transfer of the given zone but only differences from a previous serial number. This request may be ignored and a full (AXFR) sent in response if the authoritative server is unable to fulfill the request due to configuration or lack of required deltas.
OPT	41	RFC 6891	Option	This is a "pseudo DNS record type" needed to support EDNS

Obsolete record types

Progress has rendered some of the originally defined record-types obsolete. Of the records listed at IANA, some have limited use, for various reasons. Some are marked obsolete in the list, some are for very obscure services, some are for older versions of services, and some have special notes saying they are "not right".

Type	Type id.	Defining RFC	Obsoleted by	Description
MD MF MAILA	3 4 254	RFC 973	Obsoleted by: 1034, 1035	Obsoleted by RFC 973: MD(3), MF (4), MAILA (254)
MB MG MR MINFO MAILB	7 8 9 14 253	RFC 883, RFC 2505	Obsoleted by: 1034, 1035 Obsoleted by: 2050	Records to publish mailing list subscriber lists in the DNS: MB(7), MG(8), MR(9), MINFO(14), MAILB (253). The intent, as specified by RFC 883, was for MB to replace the SMTP VRFY command, MG to replace the SMTP EXPN command, and MR to replace the "551 User Not Local" SMTP error. Later, RFC 2505 recommended that both the VRFY and EXPN commands be disabled, making the use of MB and MG unlikely to ever be adopted.
WKS	11	RFC 1123		Declared "not to be relied upon" by RFC 1123 (with further information in RFC 1127): WKS(11)[12]
NB NBSTAT	32 33	RFC 1002		Mistakes: NB(32), NBSTAT(33) (from RFC 1002); the numbers are now assigned to NIMLOC and SRV.
NULL	0	RFC 883	RFC 1035	Obsoleted by RFC 1035: NULL(10) (RFC 883 defined "completion queries" (opcode 2 and maybe 3) which used this record, RFC 1035 later reassigned opcode 2 to be "status" and reserved opcode 3.)
A6	38	RFC 3363	RFC 6563	Defined as part of early IPv6 but downgraded to experimental by RFC 3363: A6(38), Later downgraded to historic in RFC 6563.
NXT KEY SIG	30 -- --	RFC 3755	RFC 4034	Obsoleted by DNSSEC updates (RFC 3755): NXT(30). At the same time, the domain of applicability for KEY and SIG was also limited to not include DNSSEC use.
		RFC 2065		Part of the first version of DNSSEC (RFC 2065).
HINFO	13			Not in current use by any notable application
RP	17			RP may be used for certain human-readable information regarding a different contact point for a specific host, subnet, or other domain level label separate than that used in the SOA record.
X25	19			Not in current use by any notable application
ISDN RT NSAP	20 21 22			Not in current use by any notable application
NSAP-PTR PX EID	23 26 31			Not in current use by any notable application
NIMLOC ATMA APL	32 34 42			Not in current use by any notable application
SINK	40			Defined by the Kitchen Sink internet draft, but never made it to RFC status: SINK(40)
GPOS	27			A more limited early version of the LOC record: GPOS(27)
UINFO UID GID UNSPEC	100 101 102 103			IANA reserved, no RFC documented them [1] and support was removed from BIND in the early 90s: UINFO(100), UID(101), GID(102), UNSPEC(103)
SPF	99	RFC 4408		SPF(99) (from RFC 4408) was specified as part of the Sender Policy Framework protocol as an alternative to storing SPF data in TXT records, using the same format. It was later found that the majority of SPF deployments lack proper support for this record type, and support for it was discontinued in RFC 7208.[13][14]