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nsupdate - Dynamic DNS update utility
nsupdate [-dv] [-y keyname:secret | -k keyfile] [-t timeout]
[-u udptimeout] [-r udpretries] [filename]
The nsupdate utility submits Dynamic DNS Update requests as defined in RFC 2136 to a name server. This utility 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 with 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 master servers identified by the MNAME field of the zone's SOA record.
Transaction signatures can be used to authenticate the Dynamic DNS updates using the TSIG resource record type described in RFC 2845. 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 that 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. The nsupdate utility does not read /etc/named.conf.
The nsupdate utility uses the -y or -k option to provide the shared secret needed to generate a TSIG record for authenticating Dynamic DNS update requests. These options are mutually exclusive. See OPTIONS.
The following options are supported:
-d
-k keyfile
-r udpretries
-t timeout
-u udptimeout
-v
-y keyname:secret
Use of the -y option is discouraged because the shared secret is supplied as a command line argument in clear text and could be visible in the output from ps(1) or in a history file maintained by the user's shell.
The nsupdate utility reads input from filename or the 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 condition 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 ]
local address [ port ]
zone zonename
class classname
key name secret
prereq nxdomain domain-name
prereq yxdomain domain-name
prereq nxrrset domain-name [ class ] type
prereq yxrrset domain-name [ class ] type
prereq yxrrset domain-name [ class ] type data...
update delete domain-name [ ttl ] [ class ] [ type [ data... ] ]
update add domain-name ttl [ class ] type data...
show
send
Lines beginning with a semicolon are comments and are ignored.
Example 1 Insert and delete resource records from the zone.
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. 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 action 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 SIG, KEY, and NXT records.)
/etc/resolv.conf
K{name}.+157.+{random}.key
K{name}.+157.+{random}.private
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 could change in future releases.
See attributes(5) for descriptions of the following attributes:
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named(1M), dnssec-keygen(1M), attributes(5)
RFC 2136, RFC 3007, RFC 2104, RFC 2845, RFC 1034, RFC 2535, RFC 2931
Source for BIND9 is available in the SUNWbind9S package.
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