nsupdate(8)
NAME
nsupdate - Dynamic DNS update utility
SYNOPSIS
nsupdate [ -d ] [ [ -y keyname:secret ] [ -k keyfile ] ] [ -v ] [ filename ]
DESCRIPTION
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 manu
ally 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. 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, appli
cations 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.
nsupdate 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. 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
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 sup
plied 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 option 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 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 prerequi
sites 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 accumu
lated 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 choosen 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. - 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 speci
fied 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 represen
tation 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. - show Displays the current message, containing all of the
prerequisites and updates specified since the last
send. - send Sends the current message. This is equivalent to
entering a blank line. - Lines beginning with a semicolon are comments, and are
ignored.
EXAMPLES
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. and an
A record for newhost.example.com it 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.ex - ample.com
> - The prerequisite condition gets the name server to check
that there are no resource records of any type for nick
name.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 con
flict 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
- /etc/resolv.conf
- used to identify default name server
- K{name}.+157.+{random}.keybase-64 encoding of HMAC-MD5 key created by dnsseckeygen(8).
- K{name}.+157.+{random}.privatebase-64 encoding of HMAC-MD5 key created by dnsseckeygen(8).
SEE ALSO
RFC2136, RFC3007, RFC2104, RFC2845, RFC1034, RFC2535,
named(8), dnssec-keygen(8).
BUGS
- 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.