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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 ...]
        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 map‐
        ping 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 var‐
        ious fields of the associated resource records that were retrieved.
 
        The arguments can be either host names (domain names) or numeric Inter‐
        net addresses.
 
        A numeric Internet address consists of four numbers separated by dots,
        eg. 192.16.199.1, representing the four bytes of the 32-bit address.
        The numbers are interpreted in hexadecimal if they begin with "0x", in
        octal if they begin with "0" and in decimal otherwise.
        The default action is to look up the associated host name.
 
        A host name or domain name consists of component names (labels) sepa‐
        rated 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 automati‐
        cally tacked on the end.  Thus a user in domain "nikhef.nl" can say
        "host nikhapo", and it will actually look up "nikhapo.nikhef.nl".  In
        all other cases, the name is tried unchanged.  Single names with trail‐
        ing 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 embed‐
        ded 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 map‐
        ping" 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 mul‐
        tiple 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 argu‐
        ments 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 regu‐
        larly 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 name‐
            server 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 informa‐
            tion to be looked up.  Supported types are listed below.  The wild‐
            card 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 avail‐
            able" (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.
 
        -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 per‐
            formed, 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.
 
        -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 regis‐
            tered 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 list‐
        ing 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 std‐
            out output (including verbose and debug printout) goes to the log‐
            file, 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.
 
        -i  constructs a query for the "reverse mapping" in-addr.arpa domain in
            case a numeric (dotted quad) address was specified.  Useful primar‐
            ily 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 nota‐
            tion, 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 for‐
            mat, 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.  Sup‐
            ported 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 out‐
            put 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 recur‐
            sion 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 repeat‐
            edly adding search domains, with the exception that the search ter‐
            minates 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.
 
        -B  Normally the search through search domains enabled by the -R option
            is stopped whenever the specified name exists but does not have the
            desired type.  This option simulates the default BIND behavior to
            continue the search.
 
        -s seconds
            specifies a new nameserver timeout value. The program will wait for
            a nameserver reply in two attempts of this number of seconds.  Nor‐
            mally it does 2 attempts of 5 seconds per nameserver address tried.
            The actual timeout algorithm is slightly more complicated, extend‐
            ing 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 vir‐
            tual 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 asymmet‐
            ric routing policy.
 
        -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.  Indi‐
        cated 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 pri‐
                  mary, 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)
 
        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 experimen‐
        tal 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)
 
        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, preci‐
                  sion)
 
        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
 
        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.  Per‐
            haps 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.
 
        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 pro‐
            vide 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 viola‐
        tions 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 speci‐
            fied server appears not to be canonical. This may cause serious
            operational problems. The canonical name is given between parenthe‐
            ses.
 
        empty zone transfer for zone from server
            The zone transfer from the specified server contained no data, per‐
            haps 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 unauthorita‐
            tive, 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.
 
        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 authori‐
            tative nameservers, the SOA information turns out to be not author‐
            itative.  This could be determined by making a query without name‐
            server recursion turned on.
 
        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 sec‐
            ondary 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.
        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 abbre‐
        viation. 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.
        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
        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 name‐
        servers must be possible for this option to work.  This option should
        be used with caution. Servers may be configured to refuse zone trans‐
        fers if they are flooded with requests.
        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
        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>
resolver(3)
 
host(1)
 

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