Open System Services Shell and Utilities Reference Manual (G06.29+, H06.08+, J06.03+)

Administrator Commands and Files nsupdate(8)
NAME
nsupdate - Starts the nonsecure BIND 9 dynamic domain name system (DNS) update utility
SYNOPSIS
/etc/dns923/nsupdate
[ -d ]
[ [-ykeyname:secret ][-kkeyfile ] ]
[ -v ]
[ filename ]
DESCRIPTION
nsupdate is used to submit Dynamic DNS Update requests (as defined in RFC2136) to a BIND 9
domain 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 flag makes nsupdate operate in debug mode. This mode 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 encryp-
tion 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 use TSIG authentication.
nsupdate does not read /etc/name d.conf.
nsupdate uses the -y or -k flag to provide the shared secret needed to generate a TSIG record for
authenticating Dynamic DNS update requests. These flags are mutually exclusive. With the -k
flag, nsupdate reads the shared secret from the file keyfile , whose name is of the form
Kname.+157.+random.private. For historical reasons, the file Kname.+157.+random.key must
also be present. When the -y flag is used, a signature is generated from keyname:secret. key-
name is the name of the key, and secret is the base64 encoded shared secret. Use of the -y flag 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.
By default, nsupdate uses UDP to send update requests to the name server. The -v flag makes
nsupdate use a TCP connection. This may be preferable when a batch of update requests is
made.
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. 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 con-
ditions 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
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