domain
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...
This RFC is an introduction to the Domain Name System (DNS), and omits
many details which can be found in a companion RFC, "Domain Names ...
... Domain Name System (DNS), and omits
many details which can be found in a companion RFC, "Domain Names -
Implementation and Specification" [RFC-1035std13]. That RFC assumes that the
...
...
However, the domain system is intentionally extensible. Researchers are
continuously proposing, implementing and experimenting with new data
...
... host address support, and the protocols and servers used to implement
domain name facilities.
...
... The history of domain names ...
...
The terms "domain" or "domain name" are used in many contexts beyond the
DNS described here. Very often, the term ...
... " are used in many contexts beyond the
DNS described here. Very often, the term domain name is used to refer
to a name with structure indicated by dots, but no relation to the DNS.
...
...
The organization of the domain system derives from some assumptions
about the needs and usage patterns of its user community and is designed
to avoid many of the the complicated problems found in general purpose
...
... organizations that have one or more hosts. Each organization
that has responsibility for a particular set of domains will
provide redundant name servers, either on the organization's
own hosts ...
... Clients of the domain system should be able to identify
trusted name servers they prefer to use before accepting
referrals to name servers outside of this "trusted" set. ...
... update
process allows updates to percolate out through the users of
the domain system rather than guaranteeing that all copies are
simultaneously updated. When updates are unavailable due to
...
... have advantages and disadvantages, but the iterative approach
is preferred for the datagram style of access. The domain
system requires implementation of the iterative approach, but
allows the recursive approach as an option. ...
...
The domain system assumes that all data originates in master files
scattered through the hosts that use the domain ...
... domain system assumes that all data originates in master files
scattered through the hosts that use the domain system. These master
files are updated by local system administrators ...
... files that are read by a local name server, and hence become available
through the name servers to users of the domain system. The user
programs access name servers through standard programs called resolvers.
...
... between
hosts (via FTP, mail, or some other mechanism); this facility is useful
when an organization wants a domain, but doesn't want to support a name
server. The organization can maintain the master files locally using a
text editor, transfer them to a foreign host ...
...
The domain system defines procedures for accessing the data and for
referrals to other name servers. The domain system also defines
...
... The domain system defines procedures for accessing the data and for
referrals to other name servers. The domain system also defines
procedures for caching retrieved data and for periodic refreshing of
data defined by the system administrator ...
...
The domain system provides:
...
... associated with the names. Conceptually, each node and leaf
of the domain name space tree names a set of information, and
query ...
... query operations are attempts to extract specific types of
information from a particular set. A query names the domain
name of interest and describes the type of resource
information that is desired. For example, the Internet
...
... information that is desired. For example, the Internet
uses some of its domain names to identify hosts; queries for
...
... NAME SERVERS are server programs which hold information about
the domain tree's structure and set information. A name
server may cache ...
... name
server may cache structure or set information about any part
of the domain tree, but in general a particular name server
...
... tree, but in general a particular name server
has complete information about a subset of the domain space,
and pointers to other name servers that can be used to lead to
information from any part of the domain ...
... domain space,
and pointers to other name servers that can be used to lead to
information from any part of the domain tree. Name servers
know the parts of the domain ...
... domain tree. Name servers
know the parts of the domain tree for which they have complete
information; a name server ...
...
These three components roughly correspond to the three layers or views
of the domain system:
...
... From the user's point of view, the domain system is accessed
through a simple procedure or OS call to a local resolver.
The domain ...
... domain system is accessed
through a simple procedure or OS call to a local resolver.
The domain space consists of a single tree and the user can
request information from any section of the tree ...
... From the resolver's point of view, the domain system is
composed of an unknown number of name servers. Each name
server has one or more pieces of the whole domain ...
... domain system is
composed of an unknown number of name servers. Each name
server has one or more pieces of the whole domain tree's data,
but the resolver views each of these databases ...
... From a name server's point of view, the domain system consists
of separate sets of local information called zones. The name
server has local copies of some of the zones. The name server ...
... DOMAIN NAME SPACE and RESOURCE RECORDS ...
... . Each node and leaf on the
tree corresponds to a resource set (which may be empty). The domain
system makes no distinctions between the uses of the interior nodes and
...
... to the root of the tree. By convention, the labels that compose a
domain name are printed or read left to right, from the most specific
(lowest, farthest from the root) to the least specific (highest, closest
...
...
Internally, programs that manipulate domain names should represent them
as sequences of labels, where each label is a length octet followed by
an octet string. Because all domain ...
... domain names should represent them
as sequences of labels, where each label is a length octet followed by
an octet string. Because all domain names end at the root, which has a
null string for a label, these internal representations can use a length
...
... root, which has a
null string for a label, these internal representations can use a length
byte of zero to terminate a domain name.
...
...
By convention, domain names can be stored with arbitrary case, but
domain name comparisons for all present domain functions are done in a
...
...
By convention, domain names can be stored with arbitrary case, but
domain name comparisons for all present domain functions are done in a
case-insensitive manner, assuming an ...
... By convention, domain names can be stored with arbitrary case, but
domain name comparisons for all present domain functions are done in a
case-insensitive manner, assuming an ASCII character set, and a high
...
... label "A" or a node with label "a", but not both as brothers; you could
refer to either using "a" or "A". When you receive a domain name or
label, you should preserve its case. The rationale for this choice is
that we may someday need to add full binary domain names ...
... domain name or
label, you should preserve its case. The rationale for this choice is
that we may someday need to add full binary domain names for new
services; existing services would not be changed.
...
...
When a user needs to type a domain name, the length of each label is
omitted and the labels are separated by dots ("."). Since a complete
domain name ends with the ...
... When a user needs to type a domain name, the length of each label is
omitted and the labels are separated by dots ("."). Since a complete
domain name ends with the root label, this leads to a printed form which
ends in a dot. We use this property to distinguish between:
...
... a character string which represents a complete domain name
(often called "absolute"). For example, "poneria.ISI.EDU."
...
... a character string that represents the starting labels of a
domain name which is incomplete, and should be completed by
local software using knowledge of the local domain (often
...
... domain name which is incomplete, and should be completed by
local software using knowledge of the local domain (often
called "relative"). For example, "poneria" used in the
ISI.EDU domain ...
...
Relative names are either taken relative to a well known origin, or to a
list of domains used as a search list. Relative names appear mostly at
the user interface ...
... user interface, where their interpretation varies from
implementation to implementation, and in master files, where they are
relative to a single origin domain name. The most common interpretation
uses the root "." as either the single origin or as one of the members
...
...
To simplify implementations, the total number of octets that represent a
domain name (i.e., the sum of all label octets and label lengths) is
limited to 255.
...
...
A domain is identified by a domain name, and consists of that part of
the domain name space that is at or below the domain name ...
... domain is identified by a domain name, and consists of that part of
the domain name space that is at or below the domain name which
specifies the domain ...
... domain name, and consists of that part of
the domain name space that is at or below the domain name which
specifies the domain. A domain ...
... domain name space that is at or below the domain name which
specifies the domain. A domain is a subdomain of another domain if it
...
... domain name which
specifies the domain. A domain is a subdomain of another domain if it
is contained within that domain ...
... specifies the domain. A domain is a subdomain of another domain if it
is contained within that domain. This relationship can be tested by
...
... domain is a subdomain of another domain if it
is contained within that domain. This relationship can be tested by
seeing if the subdomain's name ends with the containing domain's name.
...
... is contained within that domain. This relationship can be tested by
seeing if the subdomain's name ends with the containing domain's name.
For example, A.B.C.D is a subdomain of B.C.D, C.D, D, and " ".
...
... can have different implied
semantics. For example, the IN-ADDR.ARPA domain is organized and
distributed by network and host ...
... network or host numbers to names; NetBIOS domains [RFC-1001, RFC-1002] are flat because that is appropriate for that application.
...
...
Lower domains which will eventually be broken into multiple zones should
provide branching at the top of the domain so that the eventual
...
... Lower domains which will eventually be broken into multiple zones should
provide branching at the top of the domain so that the eventual
decomposition can be done without renaming. Node labels which use
...
... A convention for mapping between object names and domain
names. This describes how information about an object is
accessed.
...
... hosts, the mapping depends on the existing syntax for host names
which is a subset of the usual text representation for domain names,
together with RR formats for describing host ...
... For mailboxes, the mapping is slightly more complex. The usual mail
address <local-part>@<mail-domain> is mapped into a domain name by
converting <local-part> into a single label (regardles of dots it
...
... , the mapping is slightly more complex. The usual mail
address <local-part>@<mail-domain> is mapped into a domain name by
converting <local-part> into a single label (regardles of dots it
contains), converting <mail-domain ...
... domain name by
converting <local-part> into a single label (regardles of dots it
contains), converting <mail-domain> into a domain name using the usual
text format for domain names ...
... converting <local-part> into a single label (regardles of dots it
contains), converting <mail-domain> into a domain name using the usual
text format for domain names (dots denote label breaks), and
...
... domain> into a domain name using the usual
text format for domain names (dots denote label breaks), and
concatenating the two to form a single domain name. Thus the mailbox ...
... text format for domain names (dots denote label breaks), and
concatenating the two to form a single domain name. Thus the mailbox
HOSTMASTER@SRI-NIC ...
...
The following figure shows a part of the current domain name space, and
is used in many examples in this RFC. Note that the tree is a very
...
...
In this example, the root domain has three immediate subdomains: MIL,
EDU, and ARPA. The LCS.MIT ...
... EDU, and ARPA. The LCS.MIT.EDU domain has one immediate subdomain named
XX.LCS.MIT.EDU. All of the leaves are also domains ...
... domain has one immediate subdomain named
XX.LCS.MIT.EDU. All of the leaves are also domains.
...
... The DNS specifications attempt to be as general as possible in the rules
for constructing domain names. The idea is that the name of any
existing object can be expressed as a domain name with minimal changes.
...
... for constructing domain names. The idea is that the name of any
existing object can be expressed as a domain name with minimal changes.
However, when assigning a domain name for an object, the prudent user
...
... existing object can be expressed as a domain name with minimal changes.
However, when assigning a domain name for an object, the prudent user
will select a name which satisfies both the rules of the domain system
...
... However, when assigning a domain name for an object, the prudent user
will select a name which satisfies both the rules of the domain system
and any existing rules for the object, whether these rules are published
or implied by existing programs.
...
...
For example, when naming a mail domain, the user should satisfy both the
rules of this memo and those in RFC-822std11(-> 2822prop). When creating a new host name ...
... the old rules for HOSTS.TXT should be followed. This avoids problems
when old software is converted to use domain names.
...
...
The following syntax will result in fewer problems with many
applications that use domain names (e.g., mail, TELNET).
...
...
Note that while upper and lower case letters are allowed in domain
names, no significance is attached to the case. That is, two names with
the same spelling but different case are to be treated as if identical.
...
... which is the domain name where the RR is found. ...
... the authoritative name server for the domain ...
... a pointer to another part of the domain name space ...
... a domain name. ...
... a domain name. ...
... RDATA section of RRs is carried as a combination of
binary strings and domain names. The domain names are frequently used
as "pointers" to other data in the DNS ...
... RRs is carried as a combination of
binary strings and domain names. The domain names are frequently used
as "pointers" to other data in the DNS.
...
... RDATA section which consists of a 16 bit number
followed by a domain name. The address RRs use a standard IP address ...
...
fails to find a desired RR in the resource set associated with the
domain name, it checks to see if the resource set consists of a CNAME
record with a matching class ...
... record in the response and restarts the query at the domain name
specified in the data field of the CNAME ...
...
Domain names in RRs which point at another name should always point at
the primary name and not the alias ...
... rather than pointing at USC-ISIC.ARPA. Of course, by the robustness
principle, domain software should not fail when presented with CNAME
chains or loops; CNAME ...
... name server that does; a name server
that returns a domain name in a relevant RR may also return the RR that
...
... name server may not know all of
the classes available in the domain system, it can never know if it is
authoritative for all classes. Hence responses to QCLASS=* queries ...
... Name servers may also support inverse queries that map a particular
resource to a domain name or domain names that have that resource. For
example, while a standard query ...
... queries that map a particular
resource to a domain name or domain names that have that resource. For
example, while a standard query might map a domain name ...
... domain names that have that resource. For
example, while a standard query might map a domain name to a SOA RR, the
corresponding inverse query ...
...
The domain system cannot guarantee the completeness or uniqueness of
inverse queries because the domain ...
... domain system cannot guarantee the completeness or uniqueness of
inverse queries because the domain system is organized by domain name
rather than by host ...
... inverse queries because the domain system is organized by domain name
rather than by host address ...
...
Name servers are the repositories of information that make up the domain
database. The database is divided up into sections called zones, which
...
... A given name server will typically support one or more zones, but this
gives it authoritative information about only a small section of the
domain tree. It may also have some cached non-authoritative data about
other parts of the tree ...
...
These rules mean that every zone has at least one node, and hence domain
name, for which it is authoritative, and all of the nodes in a
particular zone are connected. Given, the tree structure ...
... It would be possible, though not particularly useful, to partition the
name space so that each domain name was in a separate zone or so that
all nodes were in a single zone. Instead, the database ...
...
When some organization wants to control its own domain, the first step
is to identify the proper parent zone, and get the parent zone's owners
to agree to the delegation ...
... that there is no requirement that the servers for a zone reside in a
host which has a name in that domain. In many cases, a zone will be
more accessible to the internet at large if its servers are widely
...
... by the same organization that manages the zone. For example, in the
current DNS, one of the name servers for the United Kingdom, or UK
domain, is found in the US. This allows US hosts to get UK data without
using limited transatlantic bandwidth ...
... query will be assumed to exist, with certain properties, unless explicit
evidence exists to the contrary. Note that the use of the term zone
here, instead of domain, is intentional; such defaults do not propagate
across zone boundaries, although a subzone may choose to achieve that
appearance by setting up ...
... wildcard RRs is of
the form "*.<anydomain>", where <anydomain> is any domain name.
<anydomain> should not contain other * labels, and should be in the
authoritative data of the zone. The wildcards ...
... When the query name or a name between the wildcard domain and
the query name is know to exist. For example, if a wildcard ...
...
This would cause any MX query for any domain name ending in X.COM to
return an MX RR pointing at A.X.COM. Two wildcard ...
...
Resolvers are programs that interface user programs to domain name
servers. In the simplest case, a resolver receives a request from a
user program (e.g., mail programs, TELNET ...
... link failure or gateway problem, or less often by coincident failure or
unavailability of all servers for a particular domain.
...
... recursive queries. This can provide an easy method of providing domain
service in a PC which lacks the resources to perform the resolver
...
... presumably needs the information in a configuration file, since it
probably lacks the sophistication to locate it in the domain database.
The user also needs to verify that the listed servers will perform the
...
... the domain name we are searching for. ...
... RRs,
starting at SNAME, then the parent domain name of SNAME, the
grandparent, and so on toward the root. Thus if SNAME were
...
... Although there are special situations, the usual choice is two of the
root servers and two of the servers for the host's domain. The reason
for two of each is for redundancy. The root servers ...
... redundancy. The root servers will provide
eventual access to all of the domain space. The two local servers will
allow the resolver to continue to resolve local names if the local
network becomes isolated from the ...
...
In our sample domain space, suppose we wanted separate administrative
control for the root, MIL, EDU, MIT ...
... In this example, the authoritative name server is shown in parentheses
at the point in the domain tree at which is assumes control.
...
... NIC.ARPA and A.ISI.EDU. The
EDU domain is served by SRI-NIC.ARPA. and C.ISI.EDU. Note that servers
...
... may have zones which are contiguous or disjoint. In this scenario,
C.ISI.EDU has contiguous zones at the root and EDU domains. A.ISI.EDU
has contiguous zones at the root and MIL domains ...
... domains. A.ISI.EDU
has contiguous zones at the root and MIL domains, but also has a non-
contiguous zone at ISI.EDU.
...
... C.ISI.EDU is a name server for the root, MIL, and EDU domains of the IN
class, and would have zones for these ...
... of the IN
class, and would have zones for these domains. The zone data for the
root domain might be:
...
... RRs marking
delegation of the MIL and EDU domains, together with the glue RRs for
the servers host ...
... The NS RRs for the MIL and EDU domains mark the boundary between the
root zone and the MIL and EDU zones. Note that in this example, the
lower zones happen to be supported by name servers which also support
...
...
The master file for the EDU zone might be stated relative to the origin
EDU. The zone data for the EDU domain might be:
...
... name server RR contents.
Relative and absolute domain names may be freely intermixed in a master
...
... it is a referral. The name server on C.ISI.EDU, realizing that it is
not authoritative for the MIL domain, has referred the requester to
servers on A.ISI.EDU and SRI-NIC.ARPA ...
... for C.ISI.EDU is authoritative. This complete reply is possible because
A.ISI.EDU happens to be authoritative for both the ARPA domain where
USC-ISIC.ARPA is found and the ISI.EDU domain ...
... Suppose the first request to the resolver comes from the local mailer,
which has mail for PVM@ISI.EDU. The mailer might then ask for type MX
RRs for the domain name ISI.EDU.
...
... search would look for NS RRs for the domains ISI.EDU, EDU,
and the root. These searches of the cache ...
... , so the
resolver would look for foreign servers to ask. No servers would match,
so it would use SBELT again. (Note that the servers for the ISI.EDU
domain are in the cache, but ISI.EDU is not an ancestor of
65.0.6.26.IN-ADDR.ARPA ...
... Name Server", IEN-116, USC/Information Sciences Institute, August 1979.
A name service obsoleted by the Domain Name System, but still in use. ...
A name service obsoleted by the Domain Name System, but still in use. ...
... D. Mills, "Internet Name Domains", RFC-799, COMSAT, September 1981. Suggests introduction of a hierarchy in place of a flat name space for the Internet ...
... Z. Su, and J. Postel, "The Domain Naming Convention for Internet User Applications", RFC-819, Network ...
... 819, Network Information Center, SRI International, August 1982.
Early thoughts on the design of the domain system. Current implementation is completely different. ...
Early thoughts on the design of the domain system. Current implementation is completely different. ...
... 830, Network Information Center, SRI International, October 1982.
Early thoughts on the design of the domain system. Current implementation is completely different. ...
Early thoughts on the design of the domain system. Current implementation is completely different. ...
... P. Mockapetris, "Domain names - Concepts and Facilities," RFC-882(-> 1035std13 | 1034std13), USC/Information Sciences Institute, November 1983.
Superceeded by this memo. ...
Superceeded by this memo. ...
... P. Mockapetris, "Domain names - Implementation and Specification," RFC-883(-> 1035std13 | 1034std13), USC/Information Sciences Institute, November 1983. Superceeded by this memo. ...
... J. Postel and J. Reynolds, "Domain Requirements", RFC-920, USC/Information Sciences Institute October 1984. Explains the naming scheme for top level domains ...
... Domain Requirements", RFC-920, USC/Information Sciences Institute October 1984. Explains the naming scheme for top level domains. ...
... P. Mockapetris, "Domain System Changes and Observations", RFC-973(-> 1035std13 | 1034std13), USC/Information Sciences Institute, January 1986.
Describes changes to RFC-882(-> 1035std13 | 1034std13) ...
Describes changes to RFC-882(-> 1035std13 | 1034std13) ...
... C. Partridge, "Mail routing and the domain system", RFC-974(-> 2821prop), CSNET CIC BBN Labs, January 1986. Describes the transition from HOSTS.TXT based mail addressing ...
... 974(-> 2821prop), CSNET CIC BBN Labs, January 1986. Describes the transition from HOSTS.TXT based mail addressing to the more powerful MX system used with the domain system. ...
... W. Lazear, "MILNET Name Domain Transition", RFC-1031, November 1987. Describes a plan for converting the MILNET to the DNS. ...
... M. K. Stahl, "Establishing a Domain - Guidelines for Administrators", RFC-1032, November 1987.
...
...
... registration policies used by the NIC to administer the top level domains and delegate subzones. ...
... Administrators Operations Guide", RFC-1033, November 1987.
A cookbook for domain administrators. ...
A cookbook for domain administrators. ...