A.1 Master File Format | DNS on Windows 2000


Team-Fly

	DNS on Windows 2000, 2nd Edition By Matt Larson, Cricket Liu
	Table of Contents

	Appendix A. DNS Message Format and Resource Records

(From RFC 1035, pages 33-35)

The format of these files is a sequence of entries. Entries are predominantly line-oriented, though parentheses can be used to continue a list of items across a line boundary, and text literals can contain CRLF within the text. Any combination of tabs and spaces acts as a delimiter between the separate items that make up an entry. The end of any line in the master file can end with a comment. The comment starts with a semicolon (;).

The following entries are defined:

 blank[  comment  ] $ORIGIN  domain-name [comment]  $INCLUDE  file-name [domain-name] [comment] domain-namerr [comment] blankrr [comment]

Blank lines, with or without comments, are allowed anywhere in the file.

Two control entries are defined: $ORIGIN and $INCLUDE. $ORIGIN is followed by a domain name and resets the current origin for relative domain names to the stated name. $INCLUDE inserts the named file into the current file and may optionally specify a domain name that sets the relative domain name origin for the included file. $INCLUDE may also have a comment. Note that an $INCLUDE entry never changes the relative origin of the parent file, regardless of changes to the relative origin made within the included file.

The last two forms represent RRs. If an entry for an RR begins with a blank, then the RR is assumed to be owned by the last stated owner. If an RR entry begins with a domain-name , then the owner name is reset.

rr contents take one of the following forms:

 [ TTL] [ class]  type RDATA [ class] [ TTL]  type RDATA

The RR begins with optional TTL and class fields, followed by a type and RDATA field appropriate to the type and class. Class and type use the standard mnemonics; TTL is a decimal integer. Omitted class and TTL values default to the last explicitly stated values. Since type and class mnemonics are disjoint , the parse is unique.

domain-name s make up a large share of the data in the master file. The labels in the domain name are expressed as character strings and separated by dots. Quoting conventions allow arbitrary characters to be stored in domain names. Domain names that end in a dot are called absolute, and are taken as complete. Domain names that do not end in a dot are called relative; the actual domain name is the concatenation of the relative part with an origin specified in an $ORIGIN, $INCLUDE, or argument to the master file-loading routine. A relative name is an error when no origin is available.

character-string is expressed in one of two ways: as a contiguous set of characters without interior spaces, or as a string beginning with " and ending with ". Inside a " -delimited string any character can occur, except for " itself, which must be quoted using a backslash (\).

Because these files are text files, several special encodings are necessary to allow arbitrary data to be loaded. In particular:

.: Of the root.
@: A free-standing @ is used to denote the current origin.
\X: Where X is any character other than a digit (0-9), \ is used to quote that character so that its special meaning does not apply. For example, \. can be used to place a dot character in a label. ^[A]

^[A] Not implemented by BIND 4.8.3.
\DDD: Where each D is a digit in the octet corresponding to the decimal number described by DDD . The resulting octet is assumed to be text and is not checked for special meaning. ^[A]

^[A] Not implemented by BIND 4.8.3.
( ): Parentheses are used to group data that crosses a line boundary. In effect, line terminations are not recognized within parentheses. ^[A]

^[A] BIND 4.8.3 allows parentheses only on SOA and WKS resource records.
;: A semicolon is used to start a comment; the remainder of the line is ignored.

A.1.1 Character Case

(From RFC 1035, page 9)

For all parts of the DNS that are part of the official protocol, all comparisons between character strings (e.g., labels, domain names, etc.) are done in a case-insensitive manner. At present, this rule is in force throughout the domain system without exception. However, future additions beyond current usage may need to use the full binary octet capabilities in names, so attempts to store domain names in 7-bit ASCII or use of special bytes to terminate labels, etc., should be avoided.

A.1.2 Types

Following is a complete list of resource record types. The textual representation is used in master files. The binary representation is used in DNS queries and responses. These resource records are described on pages 13-21 of RFC 1035.

A (address)

(From RFC 1035, page 20)

Textual representation:

  owner ttl class  A  address

Example:

 localhost.movie.edu.   IN A 127.0.0.1

Binary representation:

 Address type code: 1     +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+                         ADDRESS                         +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+

where:

ADDRESS: A 32 bit Internet address.

CNAME (canonical name)

(From RFC 1035, page 14)

Textual representation:

  owner ttl class  CNAME  canonical-dname

Example:

 wh.movie.edu.  IN  CNAME  wormhole.movie.edu.

Binary representation:

 CNAME type code: 5     +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+     /                     CNAME                     /     /                                               /     +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+

where:

CNAME: A domain-name which specifies the canonical or primary name for the owner. The owner name is an alias.

HINFO (host information)

(From RFC 1035, page 14)

Textual representation:

  owner ttl class  HINFO  cpu os

Example:

 grizzly.movie.edu.  IN  HINFO  VAX-11/780 UNIX

Binary representation:

 HINFO type code: 13     +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+     /                      CPU                      /     +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+     /                       OS                      /     +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+

where:

CPU: A character-string which specifies the CPU type.
OS: A character-string which specifies the operating system type.

MB (mailbox domain nameexperimental)

(From RFC 1035, page 14)

Textual representation:

  owner ttl class  MB  mbox-dname

Example:

 al.movie.edu.  IN  MB  robocop.movie.edu.

Binary representation:

 MB type code: 7     +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+     /                   MADNAME                     /     /                                               /     +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+

where:

MADNAME: A domain-name which specifies a host which has the specified mailbox.

MD (mail destinationobsolete)

MD has been replaced with MX.

MF (mail forwarderobsolete)

MF has been replaced with MX.

MG (mail group memberexperimental)

(From RFC 1035, page 16)

Textual representation:

  owner ttl class  MG  mgroup-dname

Example:

 admin.movie.edu.  IN  MG  al.movie.edu.                   IN  MG  ed.movie.edu.                   IN  MG  jc.movie.edu.

Binary representation:

 MG type code: 8     +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+     /                   MGMNAME                     /     /                                               /     +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+

where:

MGMNAME: A domain-name which specifies a mailbox which is a member of the mail group specified by the domain name.

MINFO (mailbox or mail list informationexperimental)

(From RFC 1035, page 16)

Textual representation:

  owner ttl class  MINFO  resp-mbox error-mbox

Example:

 admin.movie.edu.  IN  MINFO  al.movie.edu. al.movie.edu.

Binary representation:

 MINFO type code: 14     +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+     /                    RMAILBX                    /     +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+     /                    EMAILBX                    /     +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+

where:

RMAILBX: A domain-name which specifies a mailbox which is responsible for the mailing list or mailbox. If this domain name names the root, the owner of the MINFO RR is responsible for itself. Note that many existing mailing lists use a mailbox X-request for the RMAILBX field of mailing list X, e.g., Msgroup-request for Msgroup. This field provides a more general mechanism.
EMAILBX: A domain-name which specifies a mailbox which is to receive error messages related to the mailing list or mailbox specified by the owner of the MINFO RR (similar to the ERRORS-TO: field which has been proposed). If this domain name names the root, errors should be returned to the sender of the message.

MR (mail renameexperimental)

(From RFC 1035, page 17)

Textual representation:

  owner ttl class  MR  new-mbox

Example:

 eddie.movie.edu.  IN  MR  eddie.bornagain.edu.

Binary representation:

 MR type code: 9     +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+     /                   NEWNAME                     /     /                                               /     +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+

where:

NEWNAME: A domain-name which specifies a mailbox which is the proper rename of the specified mailbox.

MX (mail exchanger )

(From RFC 1035, page 17)

Textual representation:

  owner ttl class  MX  preference exchange-dname

Example:

 ora.com.  IN  MX  0  ora.ora.com.           IN  MX  10 ruby.ora.com.           IN  MX  10 opal.ora.com.

Binary representation:

 MX type code: 15     +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+                       PREFERENCE                        +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+     /                   EXCHANGE                    /     /                                               /     +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+

where:

PREFERENCE: A 16 bit integer which specifies the preference given to this RR among others at the same owner. Lower values are preferred.
EXCHANGE: A domain-name which specifies a host willing to act as a mail exchange for the owner name.

NS (name server)

(From RFC 1035, page 18)

Textual representation:

  owner ttl class  NS  name-server-dname

Example:

 movie.edu.  IN   NS  terminator.movie.edu

Binary representation:

 NS type code: 2     +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+     /                   NSDNAME                     /     /                                               /     +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+

where:

NSDNAME: A domain-name which specifies a host which should be authoritative for the specified class and domain.

NULL (nullexperimental)

(From RFC 1035, page 17)

Binary representation:

 NULL type code: 10     +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+     /  anything  /     /                                               /     +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+

Anything at all may be in the RDATA field so long as it is 65535 octets or less.

NULL is not implemented by BIND.

PTR (pointer)

(From RFC 1035, page 18)

Textual representation:

  owner ttl class  PTR  dname

Example:

 1.249.249.192.in-addr.arpa.  IN PTR wormhole.movie.edu.

Binary representation:

 PTR type code: 12     +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+     /                   PTRDNAME                    /     +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+

where:

PTRDNAME: A domain-name which points to some location in the domain name space.

SOA (start of authority)

(From RFC 1035, pages 19-20)

Textual representation:

  owner ttl class  SOA  source-dname mbox (serial refresh retry expire minimum)

Example:

 movie.edu. IN SOA terminator.movie.edu. al.robocop.movie.edu. (                       1        ; Serial                       10800    ; Refresh after 3 hours                       3600     ; Retry after 1 hour                       604800   ; Expire after 1 week                       86400 )  ; Minimum TTL of 1 day

Binary representation:

 SOA type code: 6     +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+     /                     MNAME                     /     /                                               /     +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+     /                     RNAME                     /     +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+                         SERIAL                                                                              +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+                         REFRESH                                                                             +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+                          RETRY                                                                              +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+                         EXPIRE                                                                              +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+                         MINIMUM                                                                             +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+

where:

MNAME: The domain-name of the name server that was the original or primary source of data for this zone.
RNAME: A domain-name which specifies the mailbox of the person responsible for this zone.
SERIAL: The unsigned 32 bit version number of the original copy of the zone. Zone transfers preserve this value. This value wraps and should be compared using sequence space arithmetic.
REFRESH: A 32 bit time interval before the zone should be refreshed.
RETRY: A 32 bit time interval that should elapse before a failed refresh should be retried.
EXPIRE: A 32 bit time value that specifies the upper limit on the time interval that can elapse before the zone is no longer authoritative.
MINIMUM: The unsigned 32 bit minimum TTL field that should be exported with any RR from this zone.

TXT (text)

(From RFC 1035, page 20)

Textual representation:

  owner ttl class  TXT  txt-strings

Example:

 cujo.movie.edu.  IN  TXT  "Location: machine room dog house"

Binary representation:

 TXT type code: 16     +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+     /                   TXT-DATA                    /     +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+

where:

TXT-DATA: One or more character-string s.

WKS (well-known services)

(From RFC 1035, page 21)

Textual representation:

  owner ttl class  WKS  address protocol service-list

Example:

 terminator.movie.edu.  IN  WKS 192.249.249.3  TCP ( telnet smtp ftp shell domain )

Binary representation:

 WKS type code: 11     +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+                         ADDRESS                         +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+            PROTOCOL                                    +--+--+--+--+--+--+--+--+                                                                                /  BIT MAP  /     /                                               /     +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+

where:

ADDRESS: A 32 bit Internet address.
PROTOCOL: An 8 bit IP protocol number.
BIT MAP: A variable length bit map. The bit map must be a multiple of 8 bits long.

A.1.3 New Types from RFC 1183

AFSDB (Andrew File System Data Baseexperimental)

Textual representation:

  owner ttl class  AFSDB  subtype hostname

Example:

 fx.movie.edu.  IN  AFSDB  1 bladerunner.fx.movie.edu.                IN  AFSDB  2 bladerunner.fx.movie.edu.                IN  AFSDB  1 empire.fx.movie.edu.                IN  AFSDB  2 aliens.fx.movie.edu.

Binary representation:

 AFSDB type code: 18     +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+                        SUBTYPE                          +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+     /                   HOSTNAME                    /     /                                               /     +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+

where:

SUBTYPE: Subtype 1 is an AFS cell database server. Subtype 2 is a DCE authenticated name server.
HOSTNAME: A domain-name that specifies a host that has a server for the cell named by the owner of the RR.

ISDN (Integrated Services Digital Network addressexperimental)

Textual representation:

  owner ttl class  ISDN  ISDN-address sa

Example:

 delay.hp.com.    IN  ISDN  141555514539488 hep.hp.com.      IN  ISDN  141555514539488 004

Binary representation:

 ISDN type code: 20     +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+     /                 ISDN ADDRESS                  /     +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+     /                  SUBADDRESS                   /     +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+

where:

ISDN ADDRESS: A character-string that identifies the ISDN number of owner and DDI (Direct Dial In), if any.
SUBADDRESS: An optional character-string specifying the subaddress.

RP (Responsible Personexperimental)

Textual representation:

  owner ttl class  RP  mbox-dname txt-dname

Example:

 ; The current origin is fx.movie.edu @            IN  RP   ajs.fx.movie.edu.   ajs.fx.movie.edu. bladerunner  IN  RP   root.fx.movie.edu.  hotline.fx.movie.edu.              IN  RP   richard.fx.movie.edu.  rb.fx.movie.edu. ajs          IN  TXT  "Arty Segue, (415) 555-3610" hotline      IN  TXT  "Movie U. Network Hotline, (415) 555-4111" rb           IN  TXT  "Richard Boisclair, (415) 555-9612"

Binary representation:

 RP type code: 17     +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+     /                    MAILBOX                    /     /                                               /     +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+     /                    TXTDNAME                   /     /                                               /     +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+

where:

MAILBOX: A domain-name that specifies the mailbox for the responsible person.
TXTDNAME: A domain-name for which TXT RRs exist. A subsequent query can be performed to retrieve the associated TXT resource records at txt-dname .

RT (Route Throughexperimental)

Textual representation:

  owner ttl class  RT  preference intermediate-host

Example:

 sh.prime.com.  IN  RT  2   Relay.Prime.COM.                IN  RT  10  NET.Prime.COM.

Binary representation:

 RT type code: 21     +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+                       PREFERENCE                        +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+     /                 INTERMEDIATE                  /     /                                               /     +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+

where:

PREFERENCE: A 16 bit integer that specifies the preference given to this RR among others at the same owner. Lower values are preferred.
EXCHANGE: A domain-name that specifies a host that will serve as an intermediate in reaching the host specified by owner .

X25 (X.25 addressexperimental)

Textual representation:

  owner ttl class  X25  PSDN-address

Example:

 relay.pink.com.  IN  X25   31105060845

Binary representation:

 X25 type code: 19     +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+     /                 PSDN ADDRESS                  /     +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+

where:

PSDN ADDRESS: A character-string that identifies the PSDN (Public Switched Data Network) address in the X.121 numbering plan associated with owner .

A.1.4 New Types from RFC 1664

PX (pointer to X.400/RFC 822 mapping information)

Textual representation:

  owner ttl class  PX  preference RFC822 address X.400 address

Example:

 ab.net2.it.  IN  PX  10   ab.net2.it.  O-ab.PRMD-net2.ADMDb.C-it.

Binary representation:

 PX type code: 26     +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+                       PREFERENCE                        +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+     /                    MAP822                     /     /                                               /     +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+     /                    MAPX400                    /     /                                               /     +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+

where:

PREFERENCE: A 16 bit integer which specifies the preference given to this RR among others at the same owner. Lower values are preferred.
MAP822: A domain-name element containing rfc822-domain , the RFC 822 part of the RFC 1327 mapping information.
MAPX400: A domain-name element containing the value of x400-in-domain-syntax derived from the X.400 part of the RFC 1327 mapping information.

A.1.5 New Types from RFC 2052

SRV (service location)

Textual representation:

  owner ttl class  SRV  priority weight port target

Example:

 _http._tcp.movie.edu.  IN  SRV 1 2 80 www.fx.movie.edu.                        IN  SRV 1 1 8080 www1.fx.movie.edu.

Binary representation:

 SRV type code: 33     +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+                        PRIORITY                         +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+                         WEIGHT                          +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+                          PORT                           +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+     /                    TARGET                     /     /                                               /     +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+

where:

PRIORITY: As for MX, the priority of this target host. A client MUST attempt to contact the target host with the lowest -numbered priority it can reach; target hosts with the same priority SHOULD be tried in pseudorandom order. The range is 0-65535.
WEIGHT: Load balancing mechanism. When selecting a target host among those that have the same priority, the chance of trying this one first SHOULD be proportional to its weight. The range of this number is 1-65535. Domain administrators are urged to use Weight 0 when there isn't any load balancing to do, to make the RR easier to read for humans (less noisy ).
PORT: The port on this target host of this service. The range is 0-65535. This is often as specified in Assigned Numbers but need not be.
TARGET: As for MX, the domain name of the target host. There MUST be one or more A records for this name. Implementors are urged, but not required, to return the A record(s) in the Additional Data section. Name compression is to be used for this field. A Target of "." means that the service is decidedly not available at this domain.

A.1.6 Classes

(From RFC 1035, page 13)

CLASS fields appear in resource records. The following CLASS mnemonics and values are defined:

IN: 1: the Internet
CS: 2: the CSNET class (obsoleteused only for examples in some obsolete RFCs)
CH: 3: the CHAOS class
HS: 4: the Hesiod class


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