nsupdate − Dynamic DNS update utility

nsupdate [−d] [[−y [hmac:]keyname:secret] | [−k keyfile]] [−t timeout]
[−u udptimeout] [−r udpretries] [−v] [filename]

     nsupdate is used to submit Dynamic DNS Update requests as defined in
RFC2136 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.

     The −d option makes nsupdate operate in debug mode. This provides tracing
information about the update requests that are made and the replies received
from the name server.

     Transaction signatures can be used to authenticate the Dynamic DNS updates.
These use the TSIG resource record type described in RFC2845 or the SIG(0)
record described in RFC3535 and RFC2931. TSIG relies on a shared secret that
should only be known to nsupdate and the name server. Currently, the only
supported encryption algorithm for TSIG is HMAC−MD5, which is defined in RFC
2104. Once other algorithms are defined for TSIG, applications will need to
ensure they select the appropriate algorithm as well as the key when
authenticating each other. 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. 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.  nsupdate does not read /etc/named.conf.

     nsupdate uses the −y or −k option to provide the shared secret needed to
generate a TSIG record for authenticating Dynamic DNS update requests, default
type HMAC−MD5. These options are mutually exclusive. With the −k option,
nsupdate reads the shared secret from the file keyfile, whose name is of the
form K{name}.+157.+{random}.private. For historical reasons, the file
K{name}.+157.+{random}.key must also be present. When the −y option is used, a
signature is generated from [hmac:]keyname:secret.  keyname is the name of the
key, and secret is the base64 encoded shared secret. 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.

     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


     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. The −v option makes nsupdate use a TCP connection. This may be preferable
when a batch of update requests is made.

     The −t option sets the maximum time a update request can take before it is
aborted. The default is 300 seconds. Zero can be used to disable the timeout.

     The −u option sets the UDP retry interval. The default is 3 seconds. If
zero the interval will be computed from the timeout interval and number of UDP

     The −r option sets the number of UDP retries. The default is 3. If zero
only one update request will be made.

     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

     key {name} {secret}
     Specifies that all updates are to be TSIG signed using the keyname
     keysecret pair. The key command overrides any key specified on the command
     line via −y or −k.

     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 delete {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.

     Displays the current message, containing all of the prerequisites and
     updates specified since the last send.

     Sends the current message. This is equivalent to entering a blank line.

     Displays the answer.

     Lines beginning with a semicolon are comments and are ignored.


     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
     > send

     Any A records for oldhost.example.com are deleted. and an A record for
newhost.example.com it IP address 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 RFC1034 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 RFC2535 to allow CNAMEs to
have RRSIG, DNSKEY and NSEC records.)

     used to identify default name server

     base−64 encoding of HMAC−MD5 key created by dnssec−keygen(8).

     base−64 encoding of HMAC−MD5 key created by dnssec−keygen(8).

     RFC2136(), RFC3007(), RFC2104(), RFC2845(), RFC1034(), RFC2535(),
RFC2931(), named(8), dnssec−keygen(8).

     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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Copyright © 2000−2003 Internet Software Consortium.