nsupdate(1) nsupdate(1)
NAME [Toc] [Back]
nsupdate - Dynamic DNS update utility
SYNOPSIS [Toc] [Back]
nsupdate [-d] [-v] [-y keyname:secret | -k keyfile]
DESCRIPTION [Toc] [Back]
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.
Options [Toc] [Back]
-d This 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. The signatures rely
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. nsupdate does not read
/etc/named.conf.
-k This option is used to provide the shared secret needed
to generate a TSIG record for authenticating Dynamic
DNS update requests. With this option, nsupdate reads
the shared secret from the file keyfile, whose name is
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of the form Kname.+157.+random.private. For historical
reasons, the file Kname.+157.+random.key must also be
present. This option is mutually exclusive with the -y
option.
-v This option makes nsupdate use a TCP connection to send
update requests to the name server. By default,
nsupdate uses UDP to send update requests. This may be
preferable when a batch of update requests is made.
-y This option is used to generate a signature from
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.
Input Format [Toc] [Back]
nsupdate reads commands from its 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 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.
zone zonename Specifies that all updates are to be made to the
zone zonename. If no zone statement is provided,
nsupdate will attempt to determine the correct
zone to update based on the rest of the input.
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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 (resource
records). 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 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 (IN) is assumed if class is not supplied.
update add domain-name ttl class type data..
Adds a new resource record with the specified ttl,
class and data.
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 set a specific port from where requests
are sent. If port number is not specified, the
system will assign one.
key name secret
Specifies that all updates need to be TSIG signed
using the keyname keysecret pair. The key command
overrides any key specified on the command line
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via -y or -k.
show Displays the current message, containing all the
pre-requisites and updates specified since the
last send operation.
send Sends the current message. This is equivalent to
entering a blank line.
EXAMPLES [Toc] [Back]
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
>
Any A records for oldhost.example.com are deleted. An A record for
newhost.example.com with IP address 172.16.1.1 is added. The newlyadded
record has a 1 day TTL (86400 seconds)
# nsupdate
> prereq nxdomain nickname.example.com
> update add nickname.example.com CNAME somehost.example.com
>
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 record 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 SIG, KEY and NXT records.)
FILES [Toc] [Back]
/etc/resolv.conf Used to identify default name
server.
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nsupdate(1) nsupdate(1)
Kname.+157.+random.key Base-64 encoding of HMAC-MD5 key
created by dnssec-keygen.
Kname.+157.+random.private Base-64 encoding of HMAC-MD5 key
created by dnssec-keygen.
SEE ALSO [Toc] [Back]
RFC2136 , RFC2137 , RFC2104 , RFC2845 , RFC1034 , RFC2535 , named(1M),
dnssec-keygen(1).
BUGS [Toc] [Back]
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.
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