nsupdate – Dynamic DNS update utility

       nsupdate [ -d ]  [  [ -y keyname:secret ]  [ -k keyfile ]  ]  [ -v ]  [ filename ]

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 con-
flict 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  algo-
rithms  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.

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 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 option makes nsupdate use a  TCP  connec-
tion.  This may be preferable when a batch of update requests is made.

nsupdate  reads  input from filename or standard input.  Each command is supplied on exactly one line of input.  Some com-
mands 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 authenti-
cated 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

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 iden-
tify 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 chosen 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.

class classname
Specify the default class.  If no class is specified the default class is IN.

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 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. 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 [ 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

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.

       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.

  1. # nsupdate
  2. > update delete oldhost.example.com A
  3. > update add newhost.example.com 86400 A
  4. > send

Any  A  records  for oldhost.example.com are deleted.  and an A record for newhost.example.com it IP address is
added.  The newly-added record has a 1 day TTL (86400 seconds)

  1. # nsupdate
  2. > prereq nxdomain nickname.example.com
  3. > update add nickname.example.com 86400 CNAME somehost.example.com
  4. > send

The prerequisite condition gets the name server to check that there are no resource records of any type for nickname.exam-
ple.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 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.)

              used to identify default name server

base-64 encoding of HMAC-MD5 key created by dnssec-keygen(8).

base-64 encoding of HMAC-MD5 key created by dnssec-keygen(8).

       RFC2136, RFC3007, RFC2104, RFC2845, RFC1034, RFC2535, named(8), dnssec-keygen(8).

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.

LINUX环境下:man nsupdate