nsupdate - dynamic DNS update utility
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]
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/bind/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.
- -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
/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.
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.
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.)
- /etc/resolv.conf
- Used to identify the default name server
- /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.
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.
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