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.TH "NSUPDATE" "1" "2024-02-02" "9.19.21-1-Debian" "BIND 9"
.SH NAME
nsupdate \- dynamic DNS update utility
.SH SYNOPSIS
.sp
\fBnsupdate\fP [\fB\-d\fP] [\fB\-D\fP] [\fB\-i\fP] [\fB\-L\fP level] [ [\fB\-g\fP] | [\fB\-o\fP] | [\fB\-l\fP] | [\fB\-y\fP [hmac:]keyname:secret] | [\fB\-k\fP keyfile] ] [ [\fB\-S\fP] [\fB\-K\fP tlskeyfile] [\fB\-E\fP tlscertfile] [\fB\-A\fP tlscafile] [\fB\-H\fP tlshostname] [\-O] ] [\fB\-t\fP timeout] [\fB\-u\fP udptimeout] [\fB\-r\fP udpretries] [\fB\-v\fP] [\fB\-T\fP] [\fB\-P\fP] [\fB\-V\fP] [ [\fB\-4\fP] | [\fB\-6\fP] ] [filename]
.SH DESCRIPTION
.sp
\fBnsupdate\fP is used to submit Dynamic DNS Update requests, as defined in
\fI\%RFC 2136\fP, 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.
.sp
Zones that are under dynamic control via \fBnsupdate\fP or a DHCP server
should not be edited by hand. Manual edits could conflict with dynamic
updates and cause data to be lost.
.sp
The resource records that are dynamically added or removed with
\fBnsupdate\fP must be in the same zone. Requests are sent to the
zone\(aqs primary server, which is identified by the MNAME field of the
zone\(aqs SOA record.
.sp
Transaction signatures can be used to authenticate the Dynamic DNS
updates. These use the TSIG resource record type described in \fI\%RFC 2845\fP,
the SIG(0) record described in \fI\%RFC 2535\fP and \fI\%RFC 2931\fP, or GSS\-TSIG as
described in \fI\%RFC 3645\fP\&.
.sp
TSIG relies on a shared secret that should only be known to \fBnsupdate\fP
and the name server. For instance, suitable \fBkey\fP and \fBserver\fP
statements are added to \fB/etc/bind/named.conf\fP 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. \fI\%ddns\-confgen\fP can generate suitable
configuration fragments. \fBnsupdate\fP uses the \fI\%\-y\fP or \fI\%\-k\fP options
to provide the TSIG shared secret; these options are mutually exclusive.
.sp
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.
.sp
GSS\-TSIG uses Kerberos credentials. Standard GSS\-TSIG mode is switched
on with the \fI\%\-g\fP flag. A non\-standards\-compliant variant of GSS\-TSIG
used by Windows 2000 can be switched on with the \fI\%\-o\fP flag.
.SH OPTIONS
.INDENT 0.0
.TP
.B \-4
This option sets use of IPv4 only.
.UNINDENT
.INDENT 0.0
.TP
.B \-6
This option sets use of IPv6 only.
.UNINDENT
.INDENT 0.0
.TP
.B \-A tlscafile
This option specifies the file of the certificate authorities (CA) certificates
(in PEM format) in order to verify the remote server TLS certificate when
using DNS\-over\-TLS (DoT), to achieve Strict or Mutual TLS. When used, it will
override the certificates from the global certificates store, which are
otherwise used by default when \fI\%\-S\fP is enabled. This option can not
be used in conjuction with \fI\%\-O\fP, and it implies \fI\%\-S\fP\&.
.UNINDENT
.INDENT 0.0
.TP
.B \-C
Overrides the default \fIresolv.conf\fP file. This is only intended for testing.
.UNINDENT
.INDENT 0.0
.TP
.B \-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.
.UNINDENT
.INDENT 0.0
.TP
.B \-D
This option sets extra debug mode.
.UNINDENT
.INDENT 0.0
.TP
.B \-E tlscertfile
This option sets the certificate(s) file for authentication for the
DNS\-over\-TLS (DoT) transport to the remote server. The certificate
chain file is expected to be in PEM format. This option implies \fI\%\-S\fP,
and can only be used with \fI\%\-K\fP\&.
.UNINDENT
.INDENT 0.0
.TP
.B \-g
This option enables standard GSS\-TSIG mode.
.UNINDENT
.INDENT 0.0
.TP
.B \-H tlshostname
This option makes \fBnsupdate\fP use the provided hostname during remote
server TLS certificate verification. Otherwise, the DNS server name
is used. This option implies \fI\%\-S\fP\&.
.UNINDENT
.INDENT 0.0
.TP
.B \-i
This option forces interactive mode, even when standard input is not a terminal.
.UNINDENT
.INDENT 0.0
.TP
.B \-k keyfile
This option indicates the file containing the TSIG authentication key. Keyfiles may be in
two formats: a single file containing a \fI\%named.conf\fP\-format \fBkey\fP
statement, which may be generated automatically by \fI\%ddns\-confgen\fP;
or a pair of files whose names are of the format
\fBK{name}.+157.+{random}.key\fP and
\fBK{name}.+157.+{random}.private\fP, which can be generated by
\fI\%dnssec\-keygen\fP\&. The \fI\%\-k\fP 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.
.UNINDENT
.INDENT 0.0
.TP
.B \-K tlskeyfile
This option sets the key file for authenticated encryption for the
DNS\-over\-TLS (DoT) transport with the remote server. The private key file is
expected to be in PEM format. This option implies \fI\%\-S\fP, and can only
be used with \fI\%\-E\fP\&.
.UNINDENT
.INDENT 0.0
.TP
.B \-l
This option sets local\-host only mode, which sets the server address to localhost
(disabling the \fBserver\fP so that the server address cannot be
overridden). Connections to the local server use a TSIG key
found in \fB/run/session.key\fP, which is automatically
generated by \fI\%named\fP if any local \fBprimary\fP zone has set
\fBupdate\-policy\fP to \fBlocal\fP\&. The location of this key file can be
overridden with the \fI\%\-k\fP option.
.UNINDENT
.INDENT 0.0
.TP
.B \-L level
This option sets the logging debug level. If zero, logging is disabled.
.UNINDENT
.INDENT 0.0
.TP
.B \-o
This option is deprecated. Previously, it enabled a
non\-standards\-compliant variant of GSS\-TSIG that was used by Windows
2000. Since that OS is now long past its end of life, this option is
now treated as a synonym for \fI\%\-g\fP\&.
.UNINDENT
.INDENT 0.0
.TP
.B \-O
This option enables Opportunistic TLS. When used, the remote peer\(aqs TLS
certificate will not be verified. This option should be used for debugging
purposes only, and it is not recommended to use it in production. This
option can not be used in conjuction with \fI\%\-A\fP, and it implies
\fI\%\-S\fP\&.
.UNINDENT
.INDENT 0.0
.TP
.B \-p port
This option sets the port to use for connections to a name server. The default is
53.
.UNINDENT
.INDENT 0.0
.TP
.B \-P
This option prints the list of private BIND\-specific resource record types whose
format is understood by \fBnsupdate\fP\&. See also the \fI\%\-T\fP option.
.UNINDENT
.INDENT 0.0
.TP
.B \-r udpretries
This option sets the number of UDP retries. The default is 3. If zero, only one update
request is made.
.UNINDENT
.INDENT 0.0
.TP
.B \-S
This option indicates whether to use DNS\-over\-TLS (DoT) when querying
name servers specified by \fBserver servername port\fP syntax in the input
file, and the primary server discovered through a SOA request. When the
\fI\%\-K\fP and \fI\%\-E\fP options are used, then the specified TLS
client certificate and private key pair are used for authentication
(Mutual TLS). This option implies \fI\%\-v\fP\&.
.UNINDENT
.INDENT 0.0
.TP
.B \-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 for TCP mode. For UDP mode,
the option \fI\%\-u\fP takes precedence over this option, unless the option \fI\%\-u\fP
is set to zero, in which case the interval is computed from the \fI\%\-t\fP timeout interval
and the number of UDP retries. For UDP mode, the timeout can not be disabled, and will
be rounded up to 1 second in case if both \fI\%\-t\fP and \fI\%\-u\fP are set to zero.
.UNINDENT
.INDENT 0.0
.TP
.B \-T
This option prints the list of IANA standard resource record types whose format is
understood by \fBnsupdate\fP\&. \fBnsupdate\fP exits after the lists
are printed. The \fI\%\-T\fP option can be combined with the \fI\%\-P\fP
option.
.sp
Other types can be entered using \fBTYPEXXXXX\fP where \fBXXXXX\fP 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>).
.UNINDENT
.INDENT 0.0
.TP
.B \-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.
.UNINDENT
.INDENT 0.0
.TP
.B \-v
This option specifies that TCP should be used even for small update requests. By default, \fBnsupdate\fP 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.
.UNINDENT
.INDENT 0.0
.TP
.B \-V
This option prints the version number and exits.
.UNINDENT
.INDENT 0.0
.TP
.B \-y [hmac:]keyname:secret
This option sets the literal TSIG authentication key. \fBkeyname\fP is the name of the key,
and \fBsecret\fP is the base64 encoded shared secret. \fBhmac\fP is the
name of the key algorithm; valid choices are \fBhmac\-md5\fP,
\fBhmac\-sha1\fP, \fBhmac\-sha224\fP, \fBhmac\-sha256\fP, \fBhmac\-sha384\fP, or
\fBhmac\-sha512\fP\&. If \fBhmac\fP is not specified, the default is
\fBhmac\-md5\fP, or if MD5 was disabled, \fBhmac\-sha256\fP\&.
.sp
NOTE: Use of the \fI\%\-y\fP 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\(aqs shell.
.UNINDENT
.SH INPUT FORMAT
.sp
\fBnsupdate\fP reads input from \fBfilename\fP 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.
.sp
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 \fBsend\fP command) causes the
accumulated commands to be sent as one Dynamic DNS update request to the
name server.
.sp
The command formats and their meanings are as follows:
.INDENT 0.0
.TP
.B \fBserver servername port\fP
This command sends all dynamic update requests to the name server \fBservername\fP\&.
When no server statement is provided, \fBnsupdate\fP sends updates
to the primary server of the correct zone. The MNAME field of that
zone\(aqs SOA record identify the primary server for that zone.
\fBport\fP is the port number on \fBservername\fP where the dynamic
update requests are sent. If no port number is specified, the default
DNS port number of 53 is used.
.sp
\fBNOTE:\fP
.INDENT 7.0
.INDENT 3.5
This command has no effect when GSS\-TSIG is in use.
.UNINDENT
.UNINDENT
.TP
.B \fBlocal address port\fP
This command sends all dynamic update requests using the local \fBaddress\fP\&. When
no local statement is provided, \fBnsupdate\fP sends updates using
an address and port chosen by the system. \fBport\fP can also
be used to force requests to come from a specific port. If no port number
is specified, the system assigns one.
.TP
.B \fBzone zonename\fP
This command specifies that all updates are to be made to the zone \fBzonename\fP\&.
If no \fBzone\fP statement is provided, \fBnsupdate\fP attempts to
determine the correct zone to update based on the rest of the input.
.TP
.B \fBclass classname\fP
This command specifies the default class. If no \fBclass\fP is specified, the default
class is \fBIN\fP\&.
.TP
.B \fBttl seconds\fP
This command specifies the default time\-to\-live, in seconds, for records to be added. The value
\fBnone\fP clears the default TTL.
.TP
.B \fBkey hmac:keyname secret\fP
This command specifies that all updates are to be TSIG\-signed using the
\fBkeyname\fP\-\fBsecret\fP pair. If \fBhmac\fP is specified, it sets
the signing algorithm in use. The default is \fBhmac\-md5\fP; if MD5
was disabled, the default is \fBhmac\-sha256\fP\&. The \fBkey\fP command overrides any key
specified on the command line via \fI\%\-y\fP or \fI\%\-k\fP\&.
.TP
.B \fBgsstsig\fP
This command uses GSS\-TSIG to sign the updates. This is equivalent to specifying
\fI\%\-g\fP on the command line.
.TP
.B \fBoldgsstsig\fP
This command is deprecated and will be removed in a future release.
Previously, it caused \fBnsupdate\fP to use the Windows 2000 version of
GSS\-TSIG to sign updates. It is now treated as a synonym for \fBgsstsig\fP\&.
.TP
.B \fBrealm [realm_name]\fP
When using GSS\-TSIG, this command specifies the use of \fBrealm_name\fP rather than the default realm
in \fBkrb5.conf\fP\&. If no realm is specified, the saved realm is
cleared.
.TP
.B \fBcheck\-names [boolean]\fP
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.
.TP
.B \fBcheck\-svbc [boolean]\fP
This command turns on or off check\-svcb processing on records to be added.
Check\-svcb has no effect on prerequisites or records to be deleted.
By default check\-svcb processing is on. If check\-svcb processing
fails, the record is not added to the UPDATE message.
.TP
.B \fBprereq nxdomain domain\-name\fP
This command requires that no resource record of any type exist with the name
\fBdomain\-name\fP\&.
.TP
.B \fBprereq yxdomain domain\-name\fP
This command requires that \fBdomain\-name\fP exist (as at least one resource
record, of any type).
.TP
.B \fBprereq nxrrset domain\-name class type\fP
This command requires that no resource record exist of the specified \fBtype\fP,
\fBclass\fP, and \fBdomain\-name\fP\&. If \fBclass\fP is omitted, IN (Internet)
is assumed.
.TP
.B \fBprereq yxrrset domain\-name class type\fP
This command requires that a resource record of the specified \fBtype\fP,
\fBclass\fP and \fBdomain\-name\fP exist. If \fBclass\fP is omitted, IN
(internet) is assumed.
.TP
.B \fBprereq yxrrset domain\-name class type data\fP
With this command, the \fBdata\fP from each set of prerequisites of this form sharing a
common \fBtype\fP, \fBclass\fP, and \fBdomain\-name\fP 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 \fBtype\fP, \fBclass\fP, and
\fBdomain\-name\fP\&. The \fBdata\fP are written in the standard text
representation of the resource record\(aqs RDATA.
.TP
.B \fBupdate delete domain\-name ttl class type data\fP
This command deletes any resource records named \fBdomain\-name\fP\&. If \fBtype\fP and
\fBdata\fP are provided, only matching resource records are removed.
The Internet class is assumed if \fBclass\fP is not supplied. The
\fBttl\fP is ignored, and is only allowed for compatibility.
.TP
.B \fBupdate add domain\-name ttl class type data\fP
This command adds a new resource record with the specified \fBttl\fP, \fBclass\fP, and
\fBdata\fP\&.
.TP
.B \fBshow\fP
This command displays the current message, containing all of the prerequisites and
updates specified since the last send.
.TP
.B \fBsend\fP
This command sends the current message. This is equivalent to entering a blank
line.
.TP
.B \fBanswer\fP
This command displays the answer.
.TP
.B \fBdebug\fP
This command turns on debugging.
.TP
.B \fBversion\fP
This command prints the version number.
.TP
.B \fBhelp\fP
This command prints a list of commands.
.UNINDENT
.sp
Lines beginning with a semicolon (;) are comments and are ignored.
.SH EXAMPLES
.sp
The examples below show how \fBnsupdate\fP can be used to insert and
delete resource records from the \fBexample.com\fP 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 \fBexample.com\fP\&.
.INDENT 0.0
.INDENT 3.5
.sp
.nf
.ft C
# nsupdate
> update delete oldhost.example.com A
> update add newhost.example.com 86400 A 172.16.1.1
> send
.ft P
.fi
.UNINDENT
.UNINDENT
.sp
Any A records for \fBoldhost.example.com\fP are deleted, and an A record
for \fBnewhost.example.com\fP with IP address 172.16.1.1 is added. The
newly added record has a TTL of 1 day (86400 seconds).
.INDENT 0.0
.INDENT 3.5
.sp
.nf
.ft C
# nsupdate
> prereq nxdomain nickname.example.com
> update add nickname.example.com 86400 CNAME somehost.example.com
> send
.ft P
.fi
.UNINDENT
.UNINDENT
.sp
The prerequisite condition tells the name server to verify that there are
no resource records of any type for \fBnickname.example.com\fP\&. 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 \fI\%RFC 1034\fP 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 \fI\%RFC 2535\fP to allow CNAMEs to have RRSIG,
DNSKEY, and NSEC records.)
.SH FILES
.INDENT 0.0
.TP
.B \fB/etc/resolv.conf\fP
Used to identify the default name server
.TP
.B \fB/run/session.key\fP
Sets the default TSIG key for use in local\-only mode
.TP
.B \fBK{name}.+157.+{random}.key\fP
Base\-64 encoding of the HMAC\-MD5 key created by \fI\%dnssec\-keygen\fP\&.
.TP
.B \fBK{name}.+157.+{random}.private\fP
Base\-64 encoding of the HMAC\-MD5 key created by \fI\%dnssec\-keygen\fP\&.
.UNINDENT
.SH SEE ALSO
.sp
\fI\%RFC 2136\fP, \fI\%RFC 3007\fP, \fI\%RFC 2104\fP, \fI\%RFC 2845\fP, \fI\%RFC 1034\fP, \fI\%RFC 2535\fP, \fI\%RFC 2931\fP,
\fI\%named(8)\fP, \fI\%dnssec\-keygen(8)\fP, \fI\%tsig\-keygen(8)\fP\&.
.SH BUGS
.sp
The TSIG key is redundantly stored in two separate files. This is a
consequence of \fBnsupdate\fP using the DST library for its cryptographic
operations, and may change in future releases.
.SH AUTHOR
Internet Systems Consortium
.SH COPYRIGHT
2024, Internet Systems Consortium
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