Name Server
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... We want name server transactions to be independent of the
communications system that carries them. Some systems may
...
... In any system that has a distributed database, a particular
name server may be presented with a query that can only be
answered by some other server. The two general approaches to
...
... local system administrators. Master files are text
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
...
... 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 which runs a name server ...
... name
server. The organization can maintain the master files locally using a
text editor, transfer them to a foreign host which runs a name server,
and then arrange with the system administrator of the name server ...
... name server,
and then arrange with the system administrator of the name server to get
the files loaded.
...
... includes the identity of local master files and instructions on which
non-local master files are to be loaded from foreign servers. The name
server uses the master files or copies to load its zones. For
resolvers, the configuration data identifies the name servers which
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... the domain tree's structure and set information. A name
server may cache structure or set information about any part
of the domain ...
... of the domain tree, but in general a particular name server
has complete information about a subset of the domain space,
...
... domain tree for which they have complete
information; a name server is said to be an AUTHORITY for
these parts of the name space ...
... servers in response to client requests. Resolvers must be
able to access at least one name server and use that name
server's information to answer a query directly, or pursue the
...
... client requests. Resolvers must be
able to access at least one name server and use that name
server's information to answer a query directly, or pursue the
query ...
... 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 tree's data,
...
... From a name server's point of view, the domain system consists
of separate sets of local information called zones. The name
server ...
... 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
must periodically refresh ...
... 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
must periodically refresh its zones from master copies in
...
... must periodically refresh its zones from master copies in
local files or foreign name servers. The name server must
concurrently process queries that arrive from resolvers.
...
... In the interests of performance, implementations may couple these
functions. For example, a resolver on the same machine as a name server
might share a database consisting of the the zones managed by the name
server ...
... name server
might share a database consisting of the the zones managed by the name
server and the cache managed by the resolver.
...
... the authoritative name server for the domain ...
... RRs are represented in binary form in the packets of the DNS protocol,
and are usually represented in highly encoded form when stored in a name
server or resolver. In this memo, we adopt a style similar to that used
in master files in order to show the contents of RRs. In this format,
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... CNAME RRs cause special action in DNS software. When a name server
fails to find a desired RR in the resource set associated with the
...
... CNAME
record with a matching class. If so, the name server includes the CNAME
record in the response and restarts ...
...
Queries are messages which may be sent to a name server to provoke a
response. In the Internet, queries ...
... datagrams or over
TCP connections. The response by the name server either answers the
question posed in the query, refers the requester to another set of name
...
... Using the query domain name, QTYPE, and QCLASS, the name server looks
for matching RRs. In addition to relevant records, the name server ...
... name server looks
for matching RRs. In addition to relevant records, the name server may
return RRs that point toward a name server ...
... name server may
return RRs that point toward a name server that has the desired
information or RRs that are expected to be useful in interpreting the
...
... RRs that are expected to be useful in interpreting the
relevant RRs. For example, a name server that doesn't have the
requested information may know a name server that does; a name server ...
... RRs. For example, a name server that doesn't have the
requested information may know a name server that does; a name server
that returns a domain name ...
... name server that doesn't have the
requested information may know a name server that does; a name server
that returns a domain name in a relevant RR ...
... Note that the QCLASS=* construct requires special interpretation
regarding authority. Since a particular name server may not know all of
the classes available in the domain ...
...
Implementation of this service is optional in a name server, but all
name servers must at least be able to understand an inverse query
...
... is divided up into sections called zones, which
are distributed among the name servers. While name servers can have
several optional functions and sources of data, the essential task of a
name server is to answer queries using data in its zones. By design,
name servers can answer queries ...
...
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. The name server marks its responses to queries
so that the requester can tell whether the response comes from
...
... of the zone are especially important to the zone's
management. These RRs are of two types: name server RRs that list, one
per RR ...
... the servers, but do not give their addresses. In particular, if the
name of the name server is itself in the subzone, we could be faced with
the situation where the NS RRs ...
... the situation where the NS RRs tell us that in order to learn a name
server's address, we should contact the server using the address we wish
...
... RRs for the servers.
These RRs are only necessary if the name server's name is "below" the
cut, and are only used as part of a referral response.
...
...
Once the proper name for the new subzone is selected, the new owners
should be required to demonstrate redundant name server support. Note
that there is no requirement that the servers for a zone reside in a
...
... Name server internals ...
...
The way that the name server answers the query depends upon whether it
is operating in recursive mode or not:
...
... The simplest mode for the client is recursive, since in this
mode the name server acts in the role of a resolver and
returns either an error or the answer, but never referrals.
...
... returns either an error or the answer, but never referrals.
This service is optional in a name server, and the name server
may also choose to restrict the clients ...
... This service is optional in a name server, and the name server
may also choose to restrict the clients which can use
...
... The use of recursive mode is limited to cases where both the client and
the name server agree to its use. The agreement is negotiated through
the use of two bits ...
... RA bit, is set or cleared by a
name server in all responses. The bit is true if the name
server is willing to provide recursive service ...
... name server in all responses. The bit is true if the name
server is willing to provide recursive service for the client,
...
... Clients may request recursive service
from any name server, though they should depend upon receiving
it only from servers which have previously sent an RA ...
... RA and RD are set in
the reply. Note that the name server should never perform recursive
service unless asked via RD, since this interferes with trouble shooting
...
... RRs that the name server thinks will prove useful to the
requester. ...
...
The actual algorithm used by the name server will depend on the local OS
and data structures used to store RRs ...
... Set or clear the value of recursion available in the response
depending on whether the name server is willing to provide
recursive service. If recursive service ...
... RRs can be thought of as instructions for synthesizing RRs.
When the appropriate conditions are met, the name server creates RRs
...
... cache, negative results with TTLs. For
example, a name server can distribute a TTL along with a name error
...
...
The method is that a name server may add an SOA RR to the additional
section of a response when that response is authoritative. The SOA must
...
...
A very important goal of the resolver is to eliminate network delay and
name server load from most requests by answering them from its cache of
prior results. It follows that caches ...
...
One option for implementing a resolver is to move the resolution
function out of the local machine and into a name server which supports
recursive queries. This can provide an easy method ...
...
All that the remaining stub needs is a list of name server addresses
that will perform the recursive requests. This type of resolver
...
... The user also needs to verify that the listed servers will perform the
recursive service; a name server is free to refuse to perform recursive
services for any or all clients. The user should consult the ...
... retransmission intervals to deal with both
lost UDP packets and dead servers; the name server can be easily
overloaded by too zealous a stub if it interprets retransmissions as new
...
...
In addition to its own resources, the resolver may also have shared
access to zones maintained by a local name server. This gives the
resolver the advantage of more rapid access, but the resolver must be
careful to never let cached information override zone data. In this
...
... configuration file, and
lists servers which should be used when the resolver
doesn't have any local information to guide name server
selection. The match count will be -1 to indicate that
no labels are known to match. ...
... ignore the cached data and consult with an authoritative server. This
is not recommended as the default. If the resolver has direct access to
a name server's zones, it should check to see if the desired data is
present in authoritative form, and if so, use the authoritative data in
preference to cached data.
...
... preference to cached data.
Step 2 looks for a name server to ask for the required data. The
general strategy is to look for locally-available name server RRs ...
... Step 2 looks for a name server to ask for the required data. The
general strategy is to look for locally-available name server RRs,
starting at SNAME, then the parent ...
... retransmission
policy actually slows response when used by multiple resolvers
contending for the same name server and even occasionally for a single
resolver. SLIST typically contains data values to control the timeouts
and keep track of previous transmissions.
...
...
In this example, the authoritative name server is shown in parentheses
at the point in the domain tree ...
... C.ISI.EDU name server ...
... RR
in a zone need specify the class. When a name server loads a zone, it
forces the TTL of all authoritative ...
...
Note the use of relative names here. The owner name for the ISI.EDU. is
stated using a relative name, as are two of the name server RR contents.
Relative and absolute domain names ...
...
The following queries and responses illustrate name server behavior.
Unless otherwise noted, the queries do not have recursion desired (RD ...
... The additional section contains the address RRs because the name server
at C.ISI.EDU guesses that the requester will need the addresses in order
...
...
This response has an empty answer section, but is not authoritative, so
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
...
... isn't very likely given that the query is for the host name of the name
server being asked, but would be common for other aliases.
...
... CNAME RR itself answers the query, and the name
server doesn't attempt to look up anything for C.ISI.EDU. (Except
possibly for the additional section.)
...
... J. Postel, "Internet Name Server", IEN-116, USC/Information Sciences Institute, August 1979.
A name service obsoleted by the Domain Name System ...
A name service obsoleted by the Domain Name System ...
... M. Solomon, L. Landweber, and D. Neuhengen, "The CSNET Name Server", Computer Networks, vol 6, nr 3, July 1982.
Describes a name service ...
Describes a name service ...