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NAME
host - query nameserver about domain names and zones
SYNOPSIS
host [-v] [-a] [-t querytype] [options] name [server]
host [-v] [-a] [-t querytype] [options] -l zone [server]
host [-v] [options] -H [-D] [-E] [-G] zone
host [-v] [options] -C zone
host [-v] [options] -A host
host [options] -x [name ...]
host [options] -X server [name ...]
OPTION SYNTAX
Besides the traditional short options (one letter with single dash,
and an optional value as separate argument), there are now also long
options in the format --keyword[=value]. Many (but not all) short
options have a long equivalent. There are several long options
without a short equivalent. The long options are not yet documented
in this manual page, but a summary of the existing long options, and
the mapping to their short alternative, is available via the command
host --help.
DESCRIPTION
host looks for information about Internet hosts and domain names. It
gets this information from a set of interconnected servers that are
spread across the world. The information is stored in the form of
"resource records" belonging to hierarchically organized "zones".
By default, the program simply converts between host names and
Internet addresses. However, with the -t, -a and -v options, it can be
used to find all of the information about domain names that is
maintained by the domain nameserver system. The information printed
consists of various fields of the associated resource records that
were retrieved.
The arguments can be either host names (domain names) or numeric
Internet addresses.
A numeric Internet address consists of four decimal numbers separated
by dots, e.g. 192.16.199.1, representing the four bytes of the 32-bit
address.
The default action is to look up the associated host name.
A host name or domain name consists of component names (labels)
separated by dots, e.g. nikhefh.nikhef.nl
The default action is to look up all of its Internet addresses.
For single names without a trailing dot, the local domain is
automatically tacked on the end. Thus a user in domain "nikhef.nl"
can say "host nikhapo", and it will actually look up
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"nikhapo.nikhef.nl". In all other cases, the name is tried unchanged.
Single names with trailing dot are considered top-level domain
specifications, e.g. "nl."
Note that the usual lookup convention for any name that does not end
with a trailing dot is to try first with the local domain appended,
and possibly other search domains. (As of BIND 4.9, names that have
embedded dots but no trailing dot are first tried ``as is'' before
appending search domains) This convention is not used by this program.
The actual suffix to tack on the end is usually the local domain as
specified in the /etc/resolv.conf file, but this can be overridden.
See below for a description of how to customize the host name lookup.
ARGUMENTS
The first argument is normally the host name (domain name) for which
you want to look up the requested information. If the first argument
is an Internet address, a query is done on the special "reverse
mapping" domain to look up its associated host name.
If the -l option is given, the first argument is a domain zone name
for which a complete listing is given. The program enters a special
zone listing mode which has several variants (see below).
The second argument is optional. It allows you to specify a particular
server to query. If you don't specify this argument, default servers
are used, as defined by the /etc/resolv.conf file.
EXTENDED SYNTAX
If the -x option is given, it extends the syntax in the sense that
multiple arguments are allowed on the command line. An optional
explicit server must now be specified using the -X option as it cannot
be given as an ordinary argument any more. The -X option implies -x.
The extended syntax allows no arguments at all, in which case the
arguments will be read from standard input. This can be a pipe,
redirection from a file, or an interactive terminal. Note that these
arguments are the names to be queried, and not command options.
Everything that appears after a '#' or ';' on an input line will be
skipped. Multiple arguments per line are allowed.
OPTIONS
There are a number of options that can be used before the specified
arguments. Some of these options are meaningful only to the people
who maintain the domain database zones. The first options are the
regularly used ones.
-v causes printout to be in a "verbose" format. All resource record
fields are printed. Without this option, the ttl and class fields
are not shown. Also the contents of the "additional information"
and "authority information" sections in the answer from the
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nameserver are printed, if present. Normally these sections are
not shown. In addition, the verbose option prints extra
information about the various actions that are taken by the
program. Note that -vv is "very verbose". This generates a lot of
output.
-t querytype
allows you to specify a particular type of resource record
information to be looked up. Supported types are listed below.
The wildcard may be written as either ANY or *. Types may be
given in upper or lower case. The default is type A for regular
lookups, and A, NS, and PTR for zone listings.
-a is equivalent to -t ANY. Note that this gives you "anything
available" (currently cached) and not "all defined data" if a
non-authoritative server is queried.
SPECIAL MODES
The following options put the program in a special mode.
-l zone
generates the listing of an entire zone.
E.g. the command
host -l nikhef.nl
will give a listing of all hosts in the "nikhef.nl" zone. The -t
option is used to filter what information is extracted, as you
would expect. The default is address information from A records,
supplemented with data from PTR and NS records.
The command
host -Z -a -l nikhef.nl
will give a complete download of the zone data for "nikhef.nl", in
the official master file format.
-H can be specified instead of the -l option. It will print the count
of the unique hostnames (names with an A record) encountered
within the zone. It will not count pseudo names like "localhost",
nor addresses associated with the zone name itself. Neither are
counted the "glue records" that are necessary to define
nameservers for the zone and its delegated zones.
By default, this option will not print any resource records.
Combined with the -S option, it will give a complete statistics
survey of the zone.
The host count may be affected by duplicate hosts (see below). To
compute the most realistic value, subtract the duplicate host
count from the total host count.
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-G implies -H, but lists the names of gateway hosts. These are the
hosts that have more than one address. Gateway hosts are not
checked for duplicate addresses.
-E implies -H, but lists the names of extrazone hosts. An extrazone
host in zone "foo.bar" is of the form "host.xxx.foo.bar" where
"xxx.foo.bar" is not defined as a delegated zone with an NS
record. This may be intentional, but also may be an error.
-D implies -H, but lists the names of duplicate hosts. These are
hosts with only one address, which is known to have been defined
also for another host with a different name, possibly even in a
different zone. This may be intentional, but also may be an
error.
-C can be specified instead of the -l option. It causes the SOA
records for the specified zone to be compared as found at each of
the authoritative nameservers for the zone (as listed in the NS
records). Nameserver recursion is turned off, and it will be
checked whether the answers are really authoritative. If a server
cannot provide an authoritative SOA record, a lame delegation of
the zone to that server is reported. Discrepancies between the
records are reported. Various sanity checks are performed.
-A enters a special address check mode.
If the first argument is a host name, its addresses will be
retrieved, and for each of the addresses it will be checked
whether they map back to the given host.
If the first argument is a dotted quad Internet address, its name
will be retrieved, and it will be checked whether the given
address is listed among the known addresses belonging to that
host.
If the -A flag is specified along with any zone listing option, a
reverse lookup of the address in each encountered A record is
performed, and it is checked whether it is registered and maps
back to the name of the A record. This applies to forward zones.
For reverse in-addr.arpa zones, it is checked whether the target
in PTR records maps to a canonical host name.
LISTING OPTIONS
The following options apply only to the special zone listing modes.
-L level
Recursively generate zone listings up to this level deep. Level 1
traverses the parent zone and all of its delegated zones. Each
additional level descends into another layer of delegated zones.
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-S prints statistics about the various types of resource records
found during zone listings, the number of various host
classifications, the number of delegated zones, and some total
statistics after recursive listings.
-p causes only the primary nameserver of a zone to be contacted for
zone transfers during zone listings. Normally, zone transfers are
obtained from any one of the authoritative servers that responds.
The primary nameserver is obtained from the SOA record of the
zone. If a specific server is given on the command line, this
option will query that server for the desired nameservers of the
zone. This can be used for testing purposes in case the zone has
not been registered yet.
-P prefserver
gives priority for zone transfers to preferred servers residing in
domains given by the comma-separated list prefserver. The more
domain component labels match, the higher the priority. If this
option is not present, priority is given to servers within your
own domain or parent domains. The order in which NS records are
issued may be unfavorable if they are subject to BIND 4.9 round-
robin reshuffling.
-N skipzone
prohibits zone transfers for the zones given by the comma-
separated list skipzone. This may be used during recursive zone
listings when certain zones are known to contain bogus information
which should be excluded from further processing.
COMMON OPTIONS
The following options can be used in both normal mode and domain
listing mode.
-d turns on debugging. Nameserver transactions are shown in detail.
Note that -dd prints even more debugging output.
-f filename
writes the resource record output to the given logfile as well as
to standard output.
-F filename
same as -f, but exchange the role of stdout and logfile. All
stdout output (including verbose and debug printout) goes to the
logfile, and stdout gets only the extra resource record output (so
that it can be used in pipes).
-I chars
suppresses warning messages about illegal domain names containing
invalid characters, by specifying such characters in the string
chars. The underscore is a good candidate.
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-i constructs a query for the "reverse mapping" in-addr.arpa domain
in case a numeric (dotted quad) address was specified. Useful
primarily for zone listing mode, since for numeric regular lookups
such query is done anyway (but with -i you see the actual PTR
resource record outcome).
-n constructs a query for the "reverse mapping" nsap.int domain in
case an nsap address was specified. This can be used to look up
the names associated with nsap addresses, or to list reverse nsap
zones. An nsap address consists of an even number of hexadecimal
digits, with a maximum of 40, optionally separated by interspersed
dots. An optional prefix "0x" is skipped. If this option is
used, all reverse nsap.int names are by default printed in forward
notation, only to improve readability. The -Z option forces the
output to be in the official zone file format.
-q be quiet and suppress various warning messages (the ones preceded
by " !!! "). Serious error messages (preceded by " *** ") are
never suppressed.
-Q selects quick mode, in which several potentially time consuming
special checks are not carried out, and statistics gathering is
skipped if not explicitly selected.
-T prints the time-to-live values during non-verbose output. By
default the ttl is shown only in verbose mode.
-Z prints the selected resource record output in full zone file
format, including trailing dot in domain names, plus ttl value and
class name.
OTHER OPTIONS
The following options are used only in special circumstances.
-c class
allows you to specify a particular resource record class.
Supported are IN, INTERNET, CS, CSNET, CH, CHAOS, HS, HESIOD, and
the wildcard ANY or *. The default class is IN.
-e excludes information about names that are not residing within the
given zone during zone listings, such as some glue records. For
regular queries, it suppresses the printing of the "additional
information" and "authority information" sections in the answer
from the nameserver.
-m is equivalent to -t MAILB, which filters any of types MB, MR, MG,
or MINFO. In addition, MR and MG records will be recursively
expanded into MB records.
-o suppresses the resource record output to stdout. Can be used in
combination with the -f option to separate the resource record
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output from verbose and debug comments and error messages.
-r causes nameserver recursion to be turned off in the request. This
means that the contacted nameserver will return only data it has
currently cached in its own database. It will not ask other
servers to retrieve the information. Note that nameserver
recursion is always turned off when checking SOA records using the
-C option. Authoritative servers should have all relevant
information available.
-R Normally querynames are assumed to be fully qualified and are
tried as such, unless it is a single name, which is always tried
(and only once) in the default domain. This option simulates the
default BIND behavior by qualifying any specified name by
repeatedly adding search domains, with the exception that the
search terminates immediately if the name exists but does not have
the desired querytype. The default search domains are constructed
from the default domain by repeatedly peeling off the first
component, until a final domain with only one dot remains.
-s seconds
specifies a new nameserver timeout value. The program will wait
for a nameserver reply in two attempts of this number of seconds.
Normally it does 2 attempts of 5 seconds per nameserver address
tried. The actual timeout algorithm is slightly more complicated,
extending the timeout value dynamically depending on the number of
tries and the number of nameserver addresses.
-u forces the use of virtual circuits (TCP) instead of datagrams
(UDP) when issuing nameserver queries. This is slower, but
potentially more reliable. Note that a virtual circuit is
automatically chosen in case a query exceeds the maximum datagram
packet size. Also if a datagram answer turns out to be truncated,
the query is retried using virtual circuit. A zone transfer is
always done via a virtual circuit.
-w causes the program to retry forever if the response to a regular
query times out. Normally it will time out after some 10 seconds
per nameserver address tried.
-V prints just the version number of the host program, and exits.
SPECIAL OPTIONS
The following options are used only in special circumstances.
-O srcaddr
Define an explicit source IP address for sending nameserver
queries. This may be necessary for multi-homed hosts with
asymmetric routing policy.
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-j minport -J maxport
Define a range of explicit port numbers to be assigned to the
source IP address of the client socket for sending the nameserver
queries and receiving the replies. Normally the kernel chooses a
random free port number. This may be an inappropriate number if
you are behind a firewall that filters random port numbers on
incoming traffic.
If only one of -j or -J is given, a single explicit port number is
defined. This is ok for UDP queries, but may not be sufficient for
TCP queries.
DEFAULT OPTIONS
Default options and parameters can be preset in an environment
variable HOST_DEFAULTS using the same syntax as on the command line.
They will be evaluated before the command line arguments.
QUERYTYPES
The following querytypes (resource record types) are supported.
Indicated within parentheses are the various kinds of data fields.
A Host address (dotted quad)
NS Authoritative nameserver (domain name)
MD Mail destination (domain name)
MF Mail forwarder (domain name)
CNAME Canonical name for an alias (domain name)
SOA Marks the start of a zone of authority (domain name of
primary, domain name of hostmaster, serial, refresh, retry,
expiration, default ttl)
MB Mailbox domain name (domain name)
MG Mail group member (domain name)
MR Mail rename domain name (domain name)
NULL Null resource record (no format or data)
WKS Well-known service description (dotted quad, protocol name,
list of services)
PTR Domain name pointer (domain name)
HINFO Host information (CPU type string, OS type string)
MINFO Mailbox or mail list information (request domain name, error
domain name)
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MX Mail exchanger (preference value, domain name)
TXT Descriptive text (one or more strings)
UINFO User information (string)
UID User identification (number)
GID Group identification (number)
UNSPEC Unspecified binary data (data)
ANY Matches information of any type available.
MAILB Matches any of types MB, MR, MG, or MINFO.
MAILA Matches any of types MD, or MF.
The following types have been defined in RFC 1183, but are not yet in
general use. They are recognized by this program.
RP Responsible person (domain name for MB, domain name for TXT)
AFSDB AFS database location (type, domain name)
X25 X25 address (address string)
ISDN ISDN address (address string, optional subaddress string)
RT Route through host (preference value, domain name)
The following types have been defined in RFC 1348, but are not yet in
general use. They are recognized by this program. RFC 1348 has
already been obsoleted by RFC 1637 and RFC 1706, which defines a new
experimental usage of NSAP records. This program has now hooks to
manipulate them.
NSAP NSAP address (encoded address)
NSAP-PTR NSAP pointer (domain name)
The following are new types as per RFC 1664 and RFC 1712. Note that
the GPOS type has been withdrawn already, and has been superseded by
the LOC type.
PX X400 to RFC822 mapping (preference value, rfc822 domain,
x400 domain)
GPOS Geographical position (longitude string, latitude string,
altitude string)
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The following types have been reserved in RFC 1700, and are defined in
RFC 2065 and revised per RFC 2035.
SIG Security signature
KEY Security key
NXT Next valid record
The IP v6 address architecture and DNS extensions are defined in RFC
1884 and RFC 1886.
AAAA IP v6 address (address spec with colons)
The following type is documented in RFC 1876.
LOC Geographical location (latitude, longitude, altitude,
precision)
The following types have been proposed, but are still in draft.
EID Endpoint identifier
NIMLOC Nimrod locator
ATMA ATM address
The following type is defined per RFC 2168.
NAPTR Naming authority URN
The following type is proposed in RFC 2052, updated by RFC 2782.
SRV Internet service information
The following type is proposed in RFC 2230.
KX Key exchanger (preference value, domain name)
The following type is defined in RFC 2538.
CERT
The following types have been proposed, but are still in draft.
A6
DNAME
SINK
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The following type is defined in RFC 2671.
OPT
EXAMPLES
A very good summary and validation of an entire zone can be obtained
with the following command:
host -G -S -C -A -L 1 zone
DIAGNOSTICS
FAILURE MESSAGES
The following messages are printed to show the reason of failure for a
particular query. The name of an explicit server, if specified, may be
included. If a special class was requested, it is also shown.
Nameserver [server] not running
The contacted server host does not have a nameserver running.
Nameserver [server] not responding
The nameserver at the contacted server host did not give a reply
within the specified time frame.
Nameserver [server] not reachable
The network route to the intended server host is blocked.
name does not exist [at server] (Authoritative answer)
The queryname does definitely not exist at all.
name does not exist [at server], try again
The queryname does not exist, but the answer was not
authoritative, so it is still undecided.
name has no type record [at server] (Authoritative answer)
The queryname is valid, but the specified type does not exist.
This status is here returned only in case authoritative.
name type record currently not present [at server]
The specified type does not exist, but we don't know whether the
queryname is valid or not. The answer was not authoritative.
Perhaps recursion was off, and no data was cached locally.
name type record not found [at server], try again
Some intermediate failure, e.g. timeout reaching a nameserver.
name type record not found [at server], server failure
Some explicit nameserver failure to process the query, due to
internal or forwarding errors. This may also be returned if the
zone data has expired at a secondary server, of when the server is
not authoritative for some class.
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name type record not found [at server], no recovery
Some irrecoverable format error, or server refusal.
name type record query refused [by server]
The contacted nameserver explicitly refused to answer the query.
Some nameservers are configured to refuse zone transfer requests
that come from arbitrary clients.
name type record not found [at server]
The exact reason for failure could not be determined. (This
should not happen).
zone has lame delegation to server
If we query a supposedly authoritative nameserver for the SOA
record of a zone, the information should be available and the
answer should be authoritative. If not, a lame delegation is
flagged. This is also done if the server turns out not to exist at
all. Ditto if we ask for a zone transfer and the server cannot
provide it.
No nameservers for zone found
It was not possible to retrieve the name of any nameserver for the
desired zone, in order to do a zone transfer.
No addresses of nameservers for zone found
We got some nameserver names, but it was not possible to retrieve
addresses for any of them.
No nameservers for zone responded
When trying all nameservers in succession to do a zone transfer,
none of them were able or willing to provide it.
WARNING AND ERROR MESSAGES
Miscellaneous warning messages may be generated. They are preceded by
" !!! " and indicate some non-fatal condition, usually during the
interpretation of the retrieved data. These messages can be
suppressed with the -q command line option.
Error messages are preceded by " *** " and indicate a serious problem,
such as format errors in the answers to queries, but also major
violations of the specifications. Those messages cannot be
suppressed.
zone has only one nameserver server
When retrieving the nameservers for a zone, it appears that only
one single nameserver exists. This is against the
recommendations.
zone nameserver server is not canonical (realserver)
When retrieving the nameservers for a zone, the name of the
specified server appears not to be canonical. This may cause
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serious operational problems. The canonical name is given between
parentheses.
empty zone transfer for zone from server
The zone transfer from the specified server contained no data,
perhaps only the SOA record. This could happen if we query the
victim of a lame delegation which happens to have the SOA record
in its cache.
extraneous NS record for name within zone from server
During a zone transfer, an NS record appears for a name which is
not a delegated subzone of the current zone.
extraneous SOA record for name within zone from server
During a zone transfer, an SOA record appears for a name which is
not the name of the current zone.
extraneous glue record for name within zone from server
During a zone transfer, a glue record is included for a name which
is not part of the zone or its delegated subzones. This is done in
some older versions of BIND. It is undesirable since
unauthoritative, or even incorrect, information may be propagated.
incomplete type record for name
When decoding the resource record data from the answer to a query,
not all required data fields were present. This is frequently the
case for HINFO records of which only one of the two data field is
encoded.
name has both NS and A records within zone from server
An A record has been defined for the delegated zone name. This is
signalled only during the transfer of the parent zone. It is not
an error, but the overall hostcount may be wrong, since the A
record is counted as a host in the parent zone. This A record is
not included in the hostcount of the delegated zone.
name type record has zero ttl
Resource records with a zero ttl value are special. They are not
cached after retrieval from an authoritative nameserver.
name type records have different ttl within zone from server
Resource records of the same name/type/class should have the same
ttl value in zone listings. This is sometimes not the case, due to
the independent definition of glue records or other information in
the parent zone, which is not kept in sync with the definition in
the delegated zone.
name type record has illegal name
The name of an A or MX record contains invalid characters. Only
alphanumeric characters and hyphen '-' are valid in components
(labels) between dots.
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name type host server has illegal name
The name of an NS or MX target host contains invalid characters.
Only alphanumeric characters and hyphen '-' are valid in
components (labels) between dots.
name type host server does not exist
The NS or MX target host server does not exist at all. In case of
NS, a lame delegation of name to server is flagged. It also
applies to the PTR target host in reverse zones.
name type host server has no A record
The NS or MX target host server has no address. In case of NS, a
lame delegation of name to server is flagged. It also applies to
the PTR target host in reverse zones.
name type host server is not canonical
The NS or MX target host server is not a canonical name. This may
cause serious operational problems during domain data retrieval,
or electronic mail delivery. It also applies to the PTR target
host in reverse zones.
name type target domain does not exist
The CNAME target domain does not exist at all.
name type target domain has no ANY record
The CNAME target domain does not seem to have any associated
resource record, although the name seems to exist.
name address A.B.C.D is not registered
The reverse lookup of the address of an A record failed in an
authoritative fashion. It was not present in the corresponding
in-addr.arpa zone.
name address A.B.C.D maps to realname
The reverse lookup of the address of an A record succeeded, but it
did not map back to the name of the A record. There may be A
records with different names for the same address. In the reverse
in-addr.arpa zone there is usually only one PTR to the
``official'' host name.
name address A.B.C.D maps to alias aliasname
In case of multiple PTR records, the first one encountered points
to the ``official'' host name. Subsequent ones are returned as
alias names via gethostbyaddr() as of BIND 4.9. Note that PTR
records are exempt from round-robin reshuffling.
zone SOA record at server is not authoritative
When checking the SOA for a zone at one of its supposedly
authoritative nameservers, the SOA information turns out to be not
authoritative. This could be determined by making a query without
nameserver recursion turned on.
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zone SOA primary server is not advertised via NS
The primary nameserver is not among the list of nameservers
retrieved via NS records for the zone. This is not an error per
se, since only publicly accessible nameservers may be advertised,
and others may be behind a firewall.
zone SOA primary server has illegal name
The name of the primary nameserver contains invalid characters.
zone SOA hostmaster mailbox has illegal mailbox
The name of the hostmaster mailbox contains invalid characters. A
common mistake is to use an RFC822 email address with a ``@'',
whereas the at-sign should have been replaced with a dot.
zone SOA serial has high bit set
Although the serial number is an unsigned 32-bit value, overflow
into the high bit can inadvertently occur by making inappropriate
use of the dotted decimal notation in the zone file. This may lead
to synchronization failures between primary and secondary servers.
zone SOA retry exceeds refresh
A failing refresh would be retried after it is time for the next
refresh.
zone SOA refresh+retry exceeds expire
The retry after a failing refresh would be done after the data has
already expired.
zone SOA expire is less than 1 week
The authoritative data at secondary servers expires after only one
week of failing refresh attempts. This is probably a little too
early under normal circumstances.
zone SOA expire is more than 6 months
Secondary servers will retry failing refresh attempts for a period
of more than 6 months before their authoritative data expires. As
BIND 8 concludes: war must have broken out.
server1 and server2 have different primary for zone
If the SOA record is different, the zone data is probably
different as well. What you get depends on which server you happen
to query.
server1 and server2 have different hostmaster for zone
If the SOA record is different, the zone data is probably
different as well. What you get depends on which server you happen
to query.
server1 and server2 have different serial for zone
This is usually not an error, but happens during the period after
the primary server has updated its zone data, but before a
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secondary performed a refresh. Nevertheless there could be an
error if a mistake has been made in properly adapting the serial
number.
server1 and server2 have different refresh for zone
If the SOA record is different, the zone data is probably
different as well. What you get depends on which server you happen
to query.
server1 and server2 have different retry for zone
If the SOA record is different, the zone data is probably
different as well. What you get depends on which server you happen
to query.
server1 and server2 have different expire for zone
If the SOA record is different, the zone data is probably
different as well. What you get depends on which server you happen
to query.
server1 and server2 have different defttl for zone
If the SOA record is different, the zone data is probably
different as well. What you get depends on which server you happen
to query.
EXIT STATUS
The program returns a zero exit status if the requested information
could be retrieved successfully, or in case zone listings or SOA
checks were performed without any serious error. Otherwise it returns
a non-zero exit status.
ENVIRONMENT
CUSTOMIZING HOST NAME LOOKUP
In general, if the name supplied by the user does not have any dots in
it, a default domain is appended to the end. This domain is usually
defined in the /etc/resolv.conf file. If not, it is derived by taking
the local hostname and taking everything after its first dot.
The user can override this, and specify a different default domain, by
defining it in the environment variable LOCALDOMAIN.
In addition, the user can supply his own single-word abbreviations for
host names. They should be in a file consisting of one line per
abbreviation. Each line contains an abbreviation, white space, and
then the fully qualified host name. The name of this file must be
specified in the environment variable HOSTALIASES.
SPECIAL CONSIDERATIONS
The complete set of resource record information for a domain name is
available from an authoritative nameserver only. Therefore, if you
query another server with the "-a" option, only a subset of the data
may be presented, since this option asks for any data that the latter
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host(1) host(1)
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server currently knows about, not all data that may possibly exist.
Note that the "-v" option shows whether an answer is authoritative or
not.
When listing a zone with the "-l" option, information will be fetched
from authoritative nameservers for that zone. This is implemented by
doing a complete zone transfer and then filtering out the information
that you have asked for. Note that direct contact with such
nameservers must be possible for this option to work. This option
should be used with caution. Servers may be configured to refuse zone
transfers if they are flooded with requests.
RELATED DOCUMENTATION
rfc819, Domain naming convention for internet applications
rfc883, Domain names - implementation and specification
rfc920, Domain requirements
rfc952, DOD Internet host table specification
rfc974, Mail routing and the domain system
rfc1032, Domain administrators guide
rfc1033, Domain administrators operations guide
rfc1034, Domain names - concepts and facilities
rfc1035, Domain names - implementation and specification
rfc1101, DNS encoding of network names and other types
rfc1122, Requirements for Internet hosts - comm. layers
rfc1123, Requirements for Internet hosts - application
rfc1183, New DNS RR definitions
rfc1348, DNS NSAP RRs
rfc1535, A security problem and proposed correction
rfc1536, Common DNS implementation errors
rfc1537, Common DNS data file configuration errors
rfc1591, Domain Name System structure and delegation
rfc1597, Address allocation for private internets
rfc1627, Network 10 considered harmful
rfc1637, DNS NSAP resource records
rfc1664, Using DNS to distribute X.400 address mappings
rfc1700, Assigned numbers
rfc1706, DNS NSAP resource records
rfc1712, DNS encoding of geographical location (GPOS)
rfc1713, Tools for DNS debugging
rfc1794, DNS support for load balancing
rfc1876, Expressing location information in the DNS (LOC)
rfc1884, IP v6 addressing architecture
rfc1886, DNS extensions to support IP v6 (AAAA)
rfc1912, Common DNS operational and configuration errors
rfc1982, Serial number arithmetic
rfc1995, Incremental zone transfer in DNS (IXFR)
rfc1996, Prompt notification of zone changes
rfc2010, Operational criteria for root nameservers
rfc2052, Specification of location of services (SRV)
rfc2065, DNS security extensions (KEY/SIG/NXT)
rfc2136, Dynamic updates in the DNS
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rfc2137, Secure DNS dynamic update
rfc2163, Using DNS to distribute global address mapping (PX)
rfc2168, Resolution of Uniform Resource Identifiers (NAPTR)
rfc2181, Clarifications to the DNS specification
rfc2230, Key exchange delegation record for the DNS (KX)
rfc2308, Negative cacheing of DNS queries
rfc2317, Classless in-addr.arpa delegation
rfc2535, DNS security extensions (KEY/SIG/NXT)
rfc2538, Storing certificates in the DNS (CERT)
rfc2541, DNS security operational considerations
rfc2671, Extension mechanisms for DNS (OPT)
rfc2782, Specifying the location of services (SRV)
AUTHOR
This program is originally from Rutgers University.
Rewritten by Eric Wassenaar, NIKHEF, <e07@nikhef.nl>
SEE ALSO
named(8), resolv.conf(5), resolver(3)
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