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RR
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... domain system, its original case should be
preserved whenever possible. In certain circumstances this cannot be
done. For example, if two RRs are stored in a database, one at x.y and
one at X.Y, they are actually stored at the same place in the database ...
... DOMAIN NAME SPACE AND RR DEFINITIONS ...
... RR definitions ...
... two octets containing one of the RR TYPE codes. ...
... resource record may be cached before the source
of the information should again be consulted. Zero
values are interpreted to mean that the RR can only be
used for the transaction in progress, and should not be
...
... 10 a null RR (EXPERIMENTAL) ...
... Standard RRs ...
...
The following RR definitions are expected to occur, at least
potentially, in all classes. In particular, NS ...
...
CNAME RRs cause no additional section processing, but name servers may
choose to restart the query ...
...
MB records cause additional section processing which looks up an A type
RRs corresponding to MADNAME.
...
... RFC-974] for details of
the new scheme. The recommended policy for dealing with MD RRs found in
a master file is to reject them, or to convert them to MX RRs with a
...
... MD RRs found in
a master file is to reject them, or to convert them to MX RRs with a
preference of 0.
...
... RFC-974] for details ofw
the new scheme. The recommended policy for dealing with MD RRs found in
a master file is to reject them, or to convert them to MX RRs with a
...
... MD RRs found in
a master file is to reject them, or to convert them to MX RRs with a
preference of 10.
...
... domain name names the root, the owner of the MINFO RR is
responsible for itself. Note that many existing mailing
lists use a mailbox ...
... 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 ...
... 16 bit integer which specifies the preference given to
this RR among others at the same owner. Lower values
are preferred. ...
... MX records cause type A additional section processing for the host
specified by EXCHANGE. The use of MX RRs is explained in detail in
[RFC-974].
...
...
NULL records cause no additional section processing. NULL RRs are not
allowed in master files. NULLs are used as placeholders in some
experimental extensions of the ...
...
The NS RR states that the named host should be expected to have a zone
starting at owner name of the specified ...
...
PTR records cause no additional section processing. These RRs are used
in special domains to point to some other location in the domain ...
... operations. However, MINIMUM is used in all query operations that
retrieve RRs from a zone. Whenever a RR is sent in a response to a
query, the ...
... query operations that
retrieve RRs from a zone. Whenever a RR is sent in a response to a
query, the TTL field is set to the maximum of the ...
... query, the TTL field is set to the maximum of the TTL field from the RR
and the MINIMUM field in the appropriate SOA. Thus MINIMUM is a lower
bound on the TTL ...
... and the MINIMUM field in the appropriate SOA. Thus MINIMUM is a lower
bound on the TTL field for all RRs in a zone. Note that this use of
MINIMUM should occur when the RRs are copied into the response and not
...
... TTL field for all RRs in a zone. Note that this use of
MINIMUM should occur when the RRs are copied into the response and not
when the zone is loaded from a master file or via a zone transfer. The
reason for this provison is to allow future dynamic update ...
... reason for this provison is to allow future dynamic update facilities to
change the SOA RR with known semantics.
...
...
WKS RRs cause no additional section processing.
...
... at full address nodes use the PTR RR to point back to the primary domain
names of the corresponding hosts.
...
...
The present system uses multiple RRs to represent multiple values of a
type rather than storing multiple values in the RDATA section of a
...
... type rather than storing multiple values in the RDATA section of a
single RR. This is less efficient for most applications, but does keep
RRs shorter. The multiple RRs assumption is incorporated in some
...
... section of a
single RR. This is less efficient for most applications, but does keep
RRs shorter. The multiple RRs assumption is incorporated in some
experimental work on ...
... single RR. This is less efficient for most applications, but does keep
RRs shorter. The multiple RRs assumption is incorporated in some
experimental work on dynamic update ...
...
In defining a new type of data, multiple RR types should not be used to
create an ordering between entries or express different formats for
equivalent ...
... equivalent bindings, instead this information should be carried in the
body of the RR and a single type used. This policy avoids problems with
caching multiple types and defining QTYPEs to match multiple types.
...
...
For example, the original form of mail exchange binding used two RR
types one to represent a "closer" exchange (MD) and one to represent a
...
... ) and one to represent a
"less close" exchange (MF). The difficulty is that the presence of one
RR type in a cache doesn't convey any information about the other
because the query ...
... service used a single type (MX) with a "preference" value in the RDATA
section which can order different RRs. However, if any MX RRs are found
in the cache ...
... RDATA
section which can order different RRs. However, if any MX RRs are found
in the cache, then all should be there.
...
... name server
+---------------------+
| Answer | RRs answering the question
+---------------------+
| Authority ...
... +---------------------+
| Authority | RRs pointing toward an authority
+---------------------+
...
... authority
+---------------------+
| Additional | RRs holding additional information
+---------------------+
...
... (QNAME). The last three
sections have the same format: a possibly empty list of concatenated
resource records (RRs). The answer section contains RRs that answer the
question; the authority ...
... sections have the same format: a possibly empty list of concatenated
resource records (RRs). The answer section contains RRs that answer the
question; the authority section contains RRs ...
... RRs that answer the
question; the authority section contains RRs that point toward an
authoritative name server; the additional records section contains RRs ...
... RRs that point toward an
authoritative name server; the additional records section contains RRs
which relate to the query, but are not strictly answers for the
...
... TYPE field, together with some more general codes which
can match more than one type of RR. ...
... two octets containing one of the RR type codes. This
field specifies the meaning of the data in the RDATA
...
... resource record may be
cached before it should be discarded. Zero values are
interpreted to mean that the RR can only be used for the
transaction in progress, and should not be cached. ...
... class specific. If this were not the case, a name server
or resolver would be required to know the format of all RRs it handled.
As yet, there are no such cases, but they may occur in future RDATA
...
... message subject to a
length field (such as the RDATA section of an RR), and compression is
used, the length of the compressed name is used in the length
...
...
Master files are text files that contain RRs in text form. Since the
contents of a zone can be expressed in the form of a list of RRs a
...
... Master files are text files that contain RRs in text form. Since the
contents of a zone can be expressed in the form of a list of RRs a
master file is most often used to define a zone, though it can be used
to list a cache ...
... to list a cache's contents. Hence, this section first discusses the
format of RRs in a master file, and then the special considerations when
a master file is used to create a zone in some name server ...
...
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
...
... 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 ...
... 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.
...
... mnemonics are disjoint, the parse is unique. (Note that this
order is different from the order used in examples and the order used in
the actual RRs; the given order allows easier parsing and defaulting.)
...
... any errors are encountered in the master file. The
rationale for this is that a single error can have widespread
consequences. For example, suppose that the RRs defining a delegation
have syntax errors; then the server will return authoritative name
...
... Exactly one SOA RR should be present at the top of the zone. ...
...
Note the use of the \ character in the SOA RR to specify the responsible
person mailbox "Action.domains ...
... and cache data structures, the data will be RRs. In designing the tree
framework the designer should recognize that ...
... vulnerable to corruption during system restarts. It can also
become full of expired RR data. In either case, it can easily
be discarded without disturbing zone data. ...
...
Both the TTL data for RRs and the timing data for refreshing activities
depends on 32 bit timers ...
... use positive 32 bit numbers for one type and negative numbers for the
other. The RRs in zones use relative times; the refresh timers and
...
...
When composing a response, RRs which are to be inserted in the
additional section, but duplicate RRs in the answer or authority ...
... When composing a response, RRs which are to be inserted in the
additional section, but duplicate RRs in the answer or authority
sections, may be omitted from the additional section.
...
...
Inverse queries take the form of a single RR in the answer section of
the message, with an empty question section. The owner name of the
query ...
... in the answer section of
the message, with an empty question section. The owner name of the
query RR and its TTL are not significant. The response carries
questions in the question section which identify all names possessing
...
... questions in the question section which identify all names possessing
the query RR WHICH THE NAME SERVER KNOWS. Since no name server knows
...
... for inverse queries. Thus an inverse query asking for an MX RR of
"Venera.isi.edu" should get the same response as a query for
...
... produce the same result as an inverse query for "IBM-pc unix". However,
this cannot be guaranteed because name servers may possess RRs that
contain character strings but the name server does not know that the
...
... query contains one or more QNAMEs, the
owner name and TTL of the RR in the answer section which defines the
inverse query is modified to exactly match an RR ...
... RR in the answer section which defines the
inverse query is modified to exactly match an RR found at the first
QNAME.
...
...
RRs returned in the inverse queries cannot be cached using the same
mechanism as is used for the replies to standard queries ...
... mechanism as is used for the replies to standard queries. One reason
for this is that a name might have multiple RRs of the same type, and
only one would appear. For example, an inverse query for a single
...
... root, is usually used because it minimizes the length of
the message. The TTL of the RR is not significant. The response to
this query might be:
...
... inverse queries may contain multiple questions when the inverse is not
unique. If the question section in the response is not empty, then the
RR in the answer section is modified to correspond to be an exact copy
of an RR at the first QNAME.
...
... unique. If the question section in the response is not empty, then the
RR in the answer section is modified to correspond to be an exact copy
of an RR at the first QNAME.
...
... stated in a format suitable to the local OS, into a search specification
for RRs at a specific name which match a specific QTYPE and QCLASS.
Where possible, the QTYPE and QCLASS should correspond to a single type
and a single class ...
... timestamp indicating the time the request began.
The timestamp is used to decide whether RRs in the database
can be used or are out of date. This timestamp ...
... can be used or are out of date. This timestamp uses the
absolute time format previously discussed for RR storage in
zones and caches. Note that when an RRs ...
... RRs TTL indicates a
relative time, the RR must be timely, since it is part of a
zone. When the RR has an absolute time, it is part of a
...
... relative time, the RR must be timely, since it is part of a
zone. When the RR has an absolute time, it is part of a
cache, and the TTL ...
... Note that using the timestamp is superior to using a current
time, since it allows RRs with TTLs of zero to be entered in
the cache ...
... hints about which servers to ask, in
the form of NS RRs, and may have to revise the query, in response to
CNAMEs, or revise the set of name servers the resolver is asking, in
...
... query (SLIST).
This list will be all NS RRs which correspond to the nearest ancestor
zone that the resolver knows about. To avoid startup problems, the
resolver should have a set of default servers which it will ask should
...
... resolver should have a set of default servers which it will ask should
it have no current NS RRs which are appropriate. The resolver then adds
to SLIST all of the known addresses for the name servers, and may start ...
... addresses. This
situation typically occurs when the glue address RRs have a
smaller TTL than the NS ...
... Parse the sections of the message, and insure that all RRs are
correctly formatted. ...
... As an optional step, check the TTLs of arriving data looking
for RRs with excessively long TTLs. If a RR has an
...
... for RRs with excessively long TTLs. If a RR has an
excessively long TTL, say greater than 1 week, either discard
...
... name server will occasionally not have a current copy of a
zone which it should have according to some NS RRs. The
resolver should simply remove the name server ...
... When several RRs of the same type are available for a
particular owner name, the resolver should either cache them
...
... resolver doesn't know whether it has a complete set, it should
not cache a possibly partial set of RRs. ...
... reason is that the cache does not necessarily contain existing
RRs or zone boundary information which is necessary to
restrict the application of the wildcard RRs ...
... RRs or zone boundary information which is necessary to
restrict the application of the wildcard RRs.
...
... RR data in responses of dubious reliability. When a resolver
receives unsolicited responses or RR ...
... RR data in responses of dubious reliability. When a resolver
receives unsolicited responses or RR data other than that
requested, it should discard it without caching it. The basic
implication is that all sanity checks ...
...
In a similar vein, when a resolver has a set of RRs for some name in a
response, and wants to cache the RRs ...
... RRs for some name in a
response, and wants to cache the RRs, it should check its cache for
already existing RRs ...
... RRs, it should check its cache for
already existing RRs. Depending on the circumstances, either the data
in the response or the cache is preferred, but the two should never be
...
... method is that the <mail-domain> is used as a domain
name to locate type MX RRs which list hosts willing to accept mail for
<mail-domain ...
... VENERA.ISI.EDU and VAXA.ISI.EDU as mail exchanges for
ISI.EDU. If a mailer had a message for Mockapetris@ISI.EDU, it would
route it by looking up MX RRs for ISI.EDU. The MX RRs at ISI.EDU name
VENERA.ISI.EDU and VAXA.ISI.EDU, and type A queries ...
... ISI.EDU. If a mailer had a message for Mockapetris@ISI.EDU, it would
route it by looking up MX RRs for ISI.EDU. The MX RRs at ISI.EDU name
VENERA.ISI.EDU and VAXA.ISI.EDU, and type A queries can find the host ...
... host
specified by the MB RR, which will in turn do the delivery to
all members, or the mailer can use the MG ...
...
In any of these cases, the response may include a Mail Information
(MINFO) RR. This RR is usually associated with a mail group, but is
...
... In any of these cases, the response may include a Mail Information
(MINFO) RR. This RR is usually associated with a mail group, but is
legal with a MB ...
... group, but is
legal with a MB. The MINFO RR identifies two mailboxes. One of these
identifies a responsible person for the original mailbox name ...
... group, etc.
The second mailbox name in the MINFO RR identifies a mailbox that should
receive error messages ...
...
New fields may be added to this RR in the future.
...