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]
[-R randomdev] [-v] [-T]
[-P] [-V] [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 have to be in the same zone. Requests are sent to the zone's
master server. This 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 or
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 would be 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 will be using TSIG authentication.
You can use ddns-confgen to 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¶
-d
Debug mode. This provides tracing information about the
update requests that are made and the replies received from the name
server.
-D
Extra debug mode.
-i
Force interactive mode, even when standard input is not a
terminal.
-k keyfile
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 may 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
Local-host only mode. This sets the server address to
localhost (disabling the server so that the server address cannot be
overridden). Connections to the local server will use a TSIG key found in
/var/run/named/session.key, which is automatically generated by named
if any local master zone has set update-policy to local. The
location of this key file can be overridden with the -k option.
-L level
Set the logging debug level. If zero, logging is
disabled.
-p port
Set the port to use for connections to a name server. The
default is 53.
-P
Print the list of private BIND-specific resource record
types whose format is understood by nsupdate. See also the -T
option.
-r udpretries
The number of UDP retries. The default is 3. If zero,
only one update request will be made.
-R randomdev
Where to obtain randomness. If the operating system does
not provide a /dev/random or equivalent device, the default source of
randomness is keyboard input. randomdev specifies the name of a character
device or file containing random data to be used instead of the default. The
special value keyboard indicates that keyboard input should be used. This
option may be specified multiple times.
-t timeout
The maximum time an update request can take before it is
aborted. The default is 300 seconds. Zero can be used to disable the
timeout.
-T
Print the list of IANA standard resource record types
whose format is understood by
nsupdate.
nsupdate will exit 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, will be parsed using the UNKNOWN rdata format,
(<backslash> <hash> <space> <length> <space>
<hexstring>).
-u udptimeout
The UDP retry interval. The default is 3 seconds. If
zero, the interval will be computed from the timeout interval and number of
UDP retries.
-v
Use TCP 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 will be used. TCP
may be preferable when a batch of update requests is made.
-V
Print the version number and exit.
-y [hmac:]keyname:secret
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 ps(1) or in a history file maintained
by the user's shell.
nsupdate reads input from filename or standard
input. Each command is supplied on exactly one line of input. Some commands
are for administrative purposes. The 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 will be 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 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 meaning are as follows:
server {servername} [port]
Sends all dynamic update requests to the name server
servername. When no server statement is provided, nsupdate will
send updates to the master server of the correct zone. The MNAME field of that
zone's SOA record will identify the master server for that zone. port
is the port number on servername where the dynamic update requests get
sent. If no port number is specified, the default DNS port number of 53 is
used.
local {address} [port]
Sends all dynamic update requests using the local
address. When no local statement is provided, nsupdate will send
updates using an address and port chosen by the system. port can
additionally be used to make requests come from a specific port. If no port
number is specified, the system will assign one.
zone {zonename}
Specifies that all updates are to be made to the zone
zonename. If no zone statement is provided, nsupdate will
attempt determine the correct zone to update based on the rest of the
input.
class {classname}
Specify the default class. If no class is
specified, the default class is IN.
ttl {seconds}
Specify the default time to live for records to be added.
The value none will clear the default ttl.
key [hmac:] {keyname} {secret}
Specifies that all updates are to be TSIG-signed using
the keyname secret pair. If hmac is specified, then it
sets the signing algorithm in use; the default is hmac-md5 or if MD5 was
disabled hmac-sha256. The key command overrides any key specified on
the command line via -y or -k.
gsstsig
Use GSS-TSIG to sign the updated. This is equivalent to
specifying -g on the command line.
oldgsstsig
Use the Windows 2000 version of GSS-TSIG to sign the
updated. This is equivalent to specifying -o on the command line.
realm {[realm_name]}
When using GSS-TSIG use 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]}
Turn 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 will not be added to the UPDATE message.
[prereq] nxdomain {domain-name}
Requires that no resource record of any type exists with
name domain-name.
[prereq] yxdomain {domain-name}
Requires that domain-name exists (has as at least
one resource record, of any type).
[prereq] nxrrset {domain-name} [class] {type}
Requires that no resource record exists of the specified
type, class and domain-name. If class is omitted,
IN (internet) is assumed.
[prereq] yxrrset {domain-name} [class] {type}
This requires that a resource record of the specified
type, class and domain-name must exist. If class
is omitted, IN (internet) is assumed.
[prereq] yxrrset {domain-name} [class] {type}
{data...}
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] del[ete] {domain-name} [ttl] [class]
[type [data...]]
Deletes any resource records named domain-name. If
type and data is provided, only matching resource records will
be 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...}
Adds a new resource record with the specified ttl,
class and data.
show
Displays the current message, containing all of the
prerequisites and updates specified since the last send.
send
Sends the current message. This is equivalent to entering
a blank line.
answer
Displays the answer.
debug
Turn on debugging.
version
Print version number.
help
Print a list of commands.
Lines beginning with a semicolon are comments and are ignored.
EXAMPLES¶
The examples below show how nsupdate could 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 are sent as one dynamic update request to the master 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 1 day TTL (86400 seconds).
# nsupdate
> prereq nxdomain nickname.example.com
> update add nickname.example.com 86400 CNAME somehost.example.com
> send
The prerequisite condition gets the name server to check 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 default name server
/var/run/named/session.key
sets the default TSIG key for use in local-only
mode
K{name}.+157.+{random}.key
K{name}.+157.+{random}.private
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, Inc.
COPYRIGHT¶
Copyright © 2000-2012, 2014-2021 Internet Systems
Consortium, Inc. ("ISC")