NAME
nsupdate — Dynamic DNS update utility
SYNOPSIS
nsupdate
[-d]
[-v]
[-y
keyname:secret
|
-k
keyfile]
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 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
- -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 RFC2104.
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 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
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.
- 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 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
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.
> 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 newly-added record has a 1 day TTL (86400 seconds)
> 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.)
WARNINGS
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.
FILES
- /etc/resolv.conf
Used to identify default name server.
- 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.