The MX resource record (RFC 1035 section 3.3.9) — a mail exchanger for the owner name: a 16-bit preference (lower is preferred) and a Domain naming the exchange host.

 +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
 |                  PREFERENCE                   |
 +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
 /                   EXCHANGE                    /
 /                                               /
 +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+

The exchange field is subject to wire-form name compression on encode (RFC 3597 section 4) and canonicalises to lower case (RFC 4034 section 6.2). The Eq and Ord instances compare the exchange in canonical wire form (via equalWireHost / compareWireHost), so Ord is canonical.

A name that resolves to a CNAME should not be used in the exchange field (RFC 2181 section 10.3, RFC 5321 section 5.1).

The SRV resource record (RFC 2782) — names the location of a service: 16-bit priority, weight, and port, plus a Domain naming the target host.

The target field is not subject to wire-form name compression on encode (RFC 3597 section 4) but compression is tolerated on decode. It canonicalises to lower case (RFC 4034 section 6.2). The Eq and Ord instances compare the target in canonical wire form (via equalWireHost / compareWireHost), so Ord is canonical.

The AFSDB resource record (RFC 1183 section 1; see also RFC 5864 section 5) — points at an AFS-cell or DCE-authentication-cell server: a 16-bit subtype tag and a Domain hostname.

The hostname field is not subject to wire-form name compression on encode but compression is tolerated on decode. It canonicalises to lower case (RFC 4034 section 6.2). The Eq and Ord instances compare the hostname in canonical wire form (via equalWireHost / compareWireHost), so Ord is canonical.

The NAPTR resource record (RFC 3403 section 4) — Naming Authority Pointer: a rewriting rule that translates the owner name into another resource via the flags/services tags, an optional regexp, and a replacement domain.

                                1  1  1  1  1  1
  0  1  2  3  4  5  6  7  8  9  0  1  2  3  4  5
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
|                     ORDER                     |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
|                   PREFERENCE                  |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
/                     FLAGS                     /
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
/                   SERVICES                    /
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
/                    REGEXP                     /
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
/                  REPLACEMENT                  /
/                                               /
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+

The replacement field is not subject to wire-form name compression on encode but compression is tolerated on decode. It canonicalises to lower case (RFC 4034 section 6.2). The Eq and Ord instances compare the replacement in canonical wire form (via equalWireHost / compareWireHost) and the character-string fields as DNS character-strings, so Ord is canonical.

Shared wire-format representation for ILNP node-identifier and locator records: NID (RFC 6742 section 2.1.1) carries a 64-bit Node-ID, and L64 (RFC 6742 section 2.3.1) carries a 64-bit IPv6 locator prefix. The type parameter n (either N_nid or N_l64) determines the RR type. Each has its own type synonym (T_nid, T_l64) and matching record pattern synonym (T_NID, T_L64) with the corresponding field-name prefix (nid, l64). The role of X_nid is nominal: the 64-bit payload means different things in each, so T_nid and T_l64 are not coercible.

Derived Ord is canonical: no embedded domain, fields compared in wire-encoding order. See T_l32 and T_lp for the rest of the ILNP record family.

  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |          Preference           |                               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               +
 |                             NodeID                            |
 +                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

X_nid specialised to NID records.

X_nid specialised to L64 records.

The L32 resource record (RFC 6742 section 2.2.1) — an ILNP 32-bit locator: a 16-bit preference and a 32-bit network locator carried in an IPv4 value.

 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|          Preference           |      Locator32 (16 MSBs)      |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|     Locator32 (16 LSBs)       |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Derived Ord is canonical: no embedded domain, fields compared in wire-encoding order. See X_nid and T_lp for the rest of the ILNP record family.

The LP resource record (RFC 6742 section 2.4.1) — an ILNP locator pointer: a 16-bit preference and a Domain naming a host that publishes locator records.

 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|          Preference           |                               /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               /
/                                                               /
/                              FQDN                             /
/                                                               /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

The FQDN field is not subject to wire-form name compression. The Eq and Ord instances compare the FQDN case-insensitively in wire form (via equalWireHost / compareWireHost).

See X_nid and T_l32 for the rest of the ILNP record family.

The AMTRELAY resource record (RFC 8777 section 4) — the relay-address for AMT (Automatic Multicast Tunneling) discovery. An 8-bit precedence, a 1-bit discovery-optional flag, a 7-bit relay-type field, and an AmtRelay value whose format depends on the type:

0       empty
1       wire-form IPv4 address
2       wire-form IPv6 address
3       uncompressed wire-form domain name
4-127   reserved (unlikely to be specified)

  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |   precedence  |D|    type     |                               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               +
 ~                            relay                              ~
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Derived Ord compares precedence, then discovery flag, then AmtRelay (constructor order, then field), matching the canonical wire-form ordering. The Domain inside an Amt_Host relay is compared case-sensitively, as is the convention for RR types defined after RFC 4034.

New variants of the AmtRelay value type are not expected, so an ADT is used to capture just the specified variants and an opaque catchall.