Updated: 2021/Apr/14


NSUPDATE(1)                         BIND 9                         NSUPDATE(1)



NAME
       nsupdate - dynamic DNS update utility

SYNOPSIS
       nsupdate [-d] [-D] [-i] [-L level] [ [-g] | [-o] | [-l] | [-y
       [hmac:]keyname:secret] | [-k keyfile] ] [-t timeout] [-u udptimeout]
       [-r udpretries] [-v] [-T] [-P] [-V] [ [-4] | [-6] ] [filename]

DESCRIPTION
       nsupdate is used to submit Dynamic DNS Update requests, as defined in
       RFC 2136, to a name server. This allows resource records to be added or
       removed from a zone without manually editing the zone file. A single
       update request can contain requests to add or remove more than one
       resource record.

       Zones that are under dynamic control via nsupdate or a DHCP server
       should not be edited by hand. Manual edits could conflict with dynamic
       updates and cause data to be lost.

       The resource records that are dynamically added or removed with
       nsupdate must be in the same zone. Requests are sent to the zone's
       primary server, which is identified by the MNAME field of the zone's
       SOA record.

       Transaction signatures can be used to authenticate the Dynamic DNS
       updates. These use the TSIG resource record type described in RFC 2845,
       the SIG(0) record described in RFC 2535 and RFC 2931, or GSS-TSIG as
       described in RFC 3645.

       TSIG relies on a shared secret that should only be known to nsupdate
       and the name server. For instance, suitable key and server statements
       are added to /etc/named.conf so that the name server can associate the
       appropriate secret key and algorithm with the IP address of the client
       application that is using TSIG authentication. ddns-confgen can
       generate suitable configuration fragments. nsupdate uses the -y or -k
       options to provide the TSIG shared secret; these options are mutually
       exclusive.

       SIG(0) uses public key cryptography. To use a SIG(0) key, the public
       key must be stored in a KEY record in a zone served by the name server.

       GSS-TSIG uses Kerberos credentials. Standard GSS-TSIG mode is switched
       on with the -g flag. A non-standards-compliant variant of GSS-TSIG used
       by Windows 2000 can be switched on with the -o flag.

OPTIONS

       -4     This option sets use of IPv4 only.

       -6     This option sets use of IPv6 only.

       -d     This option sets debug mode, which provides tracing information
              about the update requests that are made and the replies received
              from the name server.

       -D     This option sets extra debug mode.

       -i     This option forces interactive mode, even when standard input is
              not a terminal.

       -k keyfile
              This option indicates the file containing the TSIG
              authentication key. Keyfiles may be in two formats: a single
              file containing a named.conf-format key statement, which may be
              generated automatically by ddns-confgen; or a pair of files
              whose names are of the format K{name}.+157.+{random}.key and
              K{name}.+157.+{random}.private, which can be generated by
              dnssec-keygen. The -k option can also be used to specify a
              SIG(0) key used to authenticate Dynamic DNS update requests. In
              this case, the key specified is not an HMAC-MD5 key.

       -l     This option sets local-host only mode, which sets the server
              address to localhost (disabling the server so that the server
              address cannot be overridden). Connections to the local server
              use a TSIG key found in /var/run/named/session.key, which is
              automatically generated by named if any local primary zone has
              set update-policy to local. The location of this key file can be
              overridden with the -k option.

       -L level
              This option sets the logging debug level. If zero, logging is
              disabled.

       -p port
              This option sets the port to use for connections to a name
              server. The default is 53.

       -P     This option prints the list of private BIND-specific resource
              record types whose format is understood by nsupdate. See also
              the -T option.

       -r udpretries
              This option sets the number of UDP retries. The default is 3. If
              zero, only one update request is made.

       -t timeout
              This option sets the maximum time an update request can take
              before it is aborted. The default is 300 seconds. If zero, the
              timeout is disabled.

       -T     This option prints the list of IANA standard resource record
              types whose format is understood by nsupdate. nsupdate exits
              after the lists are printed. The -T option can be combined with
              the -P option.

              Other types can be entered using TYPEXXXXX where XXXXX is the
              decimal value of the type with no leading zeros. The rdata, if
              present, is parsed using the UNKNOWN rdata format, (<backslash>
              <hash> <space> <length> <space> <hexstring>).

       -u udptimeout
              This option sets the UDP retry interval. The default is 3
              seconds. If zero, the interval is computed from the timeout
              interval and number of UDP retries.

       -v     This option specifies that TCP should be used even for small
              update requests. By default, nsupdate uses UDP to send update
              requests to the name server unless they are too large to fit in
              a UDP request, in which case TCP is used. TCP may be preferable
              when a batch of update requests is made.

       -V     This option prints the version number and exits.

       -y [hmac:]keyname:secret
              This option sets the literal TSIG authentication key. keyname is
              the name of the key, and secret is the base64 encoded shared
              secret. hmac is the name of the key algorithm; valid choices are
              hmac-md5, hmac-sha1, hmac-sha224, hmac-sha256, hmac-sha384, or
              hmac-sha512. If hmac is not specified, the default is hmac-md5,
              or if MD5 was disabled, hmac-sha256.

              NOTE: Use of the -y option is discouraged because the shared
              secret is supplied as a command-line argument in clear text.
              This may be visible in the output from ps1 or in a history file
              maintained by the user's shell.

INPUT FORMAT
       nsupdate reads input from filename or standard input. Each command is
       supplied on exactly one line of input. Some commands are for
       administrative purposes; others are either update instructions or
       prerequisite checks on the contents of the zone. These checks set
       conditions that some name or set of resource records (RRset) either
       exists or is absent from the zone. These conditions must be met if the
       entire update request is to succeed. Updates are rejected if the tests
       for the prerequisite conditions fail.

       Every update request consists of zero or more prerequisites and zero or
       more updates. This allows a suitably authenticated update request to
       proceed if some specified resource records are either present or
       missing from the zone. A blank input line (or the send command) causes
       the accumulated commands to be sent as one Dynamic DNS update request
       to the name server.

       The command formats and their meanings are as follows:

       server servername port
              This command sends all dynamic update requests to the name
              server servername.  When no server statement is provided,
              nsupdate sends updates to the primary server of the correct
              zone. The MNAME field of that zone's SOA record identify the
              primary server for that zone.  port is the port number on
              servername where the dynamic update requests are sent. If no
              port number is specified, the default DNS port number of 53 is
              used.

       local address port
              This command sends all dynamic update requests using the local
              address. When no local statement is provided, nsupdate sends
              updates using an address and port chosen by the system. port can
              also be used to force requests to come from a specific port. If
              no port number is specified, the system assigns one.

       zone zonename
              This command specifies that all updates are to be made to the
              zone zonename.  If no zone statement is provided, nsupdate
              attempts to determine the correct zone to update based on the
              rest of the input.

       class classname
              This command specifies the default class. If no class is
              specified, the default class is IN.

       ttl seconds
              This command specifies the default time-to-live, in seconds, for
              records to be added. The value none clears the default TTL.

       key hmac:keyname secret
              This command specifies that all updates are to be TSIG-signed
              using the keyname-secret pair. If hmac is specified, it sets the
              signing algorithm in use. The default is hmac-md5; if MD5 was
              disabled, the default is hmac-sha256. The key command overrides
              any key specified on the command line via -y or -k.

       gsstsig
              This command uses GSS-TSIG to sign the updates. This is
              equivalent to specifying -g on the command line.

       oldgsstsig
              This command uses the Windows 2000 version of GSS-TSIG to sign
              the updates. This is equivalent to specifying -o on the command
              line.

       realm [realm_name]
              When using GSS-TSIG, this command specifies the use of
              realm_name rather than the default realm in krb5.conf. If no
              realm is specified, the saved realm is cleared.

       check-names [yes_or_no]
              This command turns on or off check-names processing on records
              to be added.  Check-names has no effect on prerequisites or
              records to be deleted.  By default check-names processing is on.
              If check-names processing fails, the record is not added to the
              UPDATE message.

       prereq nxdomain domain-name
              This command requires that no resource record of any type exist
              with the name domain-name.

       prereq yxdomain domain-name
              This command requires that domain-name exist (as at least one
              resource record, of any type).

       prereq nxrrset domain-name class type
              This command requires that no resource record exist of the
              specified type, class, and domain-name. If class is omitted, IN
              (Internet) is assumed.

       prereq yxrrset domain-name class type
              This command requires that a resource record of the specified
              type, class and domain-name exist. If class is omitted, IN
              (internet) is assumed.

       prereq yxrrset domain-name class type data
              With this command, the data from each set of prerequisites of
              this form sharing a common type, class, and domain-name are
              combined to form a set of RRs. This set of RRs must exactly
              match the set of RRs existing in the zone at the given type,
              class, and domain-name. The data are written in the standard
              text representation of the resource record's RDATA.

       update delete domain-name ttl class type data
              This command deletes any resource records named domain-name. If
              type and data are provided, only matching resource records are
              removed.  The Internet class is assumed if class is not
              supplied. The ttl is ignored, and is only allowed for
              compatibility.

       update add domain-name ttl class type data
              This command adds a new resource record with the specified ttl,
              class, and data.

       show   This command displays the current message, containing all of the
              prerequisites and updates specified since the last send.

       send   This command sends the current message. This is equivalent to
              entering a blank line.

       answer This command displays the answer.

       debug  This command turns on debugging.

       version
              This command prints the version number.

       help   This command prints a list of commands.

       Lines beginning with a semicolon (;) are comments and are ignored.

EXAMPLES
       The examples below show how nsupdate can be used to insert and delete
       resource records from the example.com zone. Notice that the input in
       each example contains a trailing blank line, so that a group of
       commands is sent as one dynamic update request to the primary name
       server for example.com.

          # nsupdate
          > update delete oldhost.example.com A
          > update add newhost.example.com 86400 A 172.16.1.1
          > send

       Any A records for oldhost.example.com are deleted, and an A record for
       newhost.example.com with IP address 172.16.1.1 is added. The newly
       added record has a TTL of 1 day (86400 seconds).

          # nsupdate
          > prereq nxdomain nickname.example.com
          > update add nickname.example.com 86400 CNAME somehost.example.com
          > send

       The prerequisite condition tells the name server to verify that there
       are no resource records of any type for nickname.example.com. If there
       are, the update request fails. If this name does not exist, a CNAME for
       it is added. This ensures that when the CNAME is added, it cannot
       conflict with the long-standing rule in RFC 1034 that a name must not
       exist as any other record type if it exists as a CNAME. (The rule has
       been updated for DNSSEC in RFC 2535 to allow CNAMEs to have RRSIG,
       DNSKEY, and NSEC records.)

FILES

       /etc/resolv.conf
              Used to identify the default name server

       /var/run/named/session.key
              Sets the default TSIG key for use in local-only mode

       K{name}.+157.+{random}.key
              Base-64 encoding of the HMAC-MD5 key created by dnssec-keygen.

       K{name}.+157.+{random}.private
              Base-64 encoding of the HMAC-MD5 key created by dnssec-keygen.

SEE ALSO
       RFC 2136, RFC 3007, RFC 2104, RFC 2845, RFC 1034, RFC 2535, RFC 2931,
       named(8), ddns-confgen(8), dnssec-keygen(8).

BUGS
       The TSIG key is redundantly stored in two separate files. This is a
       consequence of nsupdate using the DST library for its cryptographic
       operations, and may change in future releases.

AUTHOR
       Internet Systems Consortium

COPYRIGHT
       2021, Internet Systems Consortium



9.16.20                                                            NSUPDATE(1)