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.

-C Overrides the default resolv.conf file. This is only intended
for testing.

-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.

-g This option enables standard GSS-TSIG 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/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.

-o This option enables a non-standards-compliant variant of
GSS-TSIG used by Windows 2000.

-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 for TCP mode. For UDP mode, the option -u
takes precedence over this option, unless the option -u is set
to zero, in which case the interval is computed from the -t
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 -t and -u are set to zero.

-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.

NOTE:
This command has no effect when GSS-TSIG is in use.

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 [boolean]
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/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), dnssec-keygen(8), tsig-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

2025, Internet Systems Consortium

9.18.34 2025-02-11 NSUPDATE(1)