2014-04-18
ISC Internet Systems Consortium, Inc.
nsupdate 1 BIND9
nsupdate Dynamic DNS update utility
2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2014 2015 2016 2017 2018 Internet Systems Consortium, Inc. ("ISC")
`nsupdate` `-d` `-D` `-i` `-L level` `-g` `-o` `-l` `-y hmac:keyname:secret` `-k keyfile` `-t timeout` `-u udptimeout` `-r udpretries` `-R randomdev` `-v` `-T` `-P` `-V` `-4` `-6` filename

## DESCRIPTION

`nsupdate` is used to submit Dynamic DNS Update requests as defined in RFC 2136 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.

Transaction signatures can be used to authenticate the Dynamic DNS updates. These use the TSIG resource record type described in RFC 2845 or the SIG(0) record described in RFC 2535 and RFC 2931 or GSS-TSIG as described in RFC 3645.

TSIG relies on a shared secret that should only be known to `nsupdate` and the name server. 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. You can use `ddns-confgen` to generate suitable configuration fragments. `nsupdate` uses the `-y` or `-k` options to provide the TSIG shared secret. These options are mutually exclusive.

SIG(0) uses public key cryptography. To use a SIG(0) key, the public key must be stored in a KEY record in a zone served by the name server.

GSS-TSIG uses Kerberos credentials. Standard GSS-TSIG mode is switched on with the `-g` flag. A non-standards-compliant variant of GSS-TSIG used by Windows 2000 can be switched on with the `-o` flag.

## OPTIONS

-4

  Use IPv4 only.

-6

  Use IPv6 only.

-d

  Debug mode. This provides tracing information about the update requests that are made and the replies received from the name server.

-D

  Extra debug mode.

-i

  Force interactive mode, even when standard input is not a terminal.

-k keyfile

  The file containing the TSIG authentication key. Keyfiles may be in two formats: a single file containing a `named.conf`-format `key` statement, which may be generated automatically by `ddns-confgen`, or a pair of files whose names are of the format `K{name}.+157.+{random}.key` and `K{name}.+157.+{random}.private`, which can be generated by `dnssec-keygen`. The `-k` may also be used to specify a SIG(0) key used to authenticate Dynamic DNS update requests. In this case, the key specified is not an HMAC-MD5 key.

-l

  Local-host only mode. This sets the server address to localhost (disabling the `server` so that the server address cannot be overridden). Connections to the local server will use a TSIG key found in `/var/run/named/session.key`, which is automatically generated by `named` if any local master zone has set `update-policy` to `local`. The location of this key file can be overridden with the `-k` option.

-L level

  Set the logging debug level. If zero, logging is disabled.

-p port

  Set the port to use for connections to a name server. The default is 53.

-P

  Print the list of private BIND-specific resource record types whose format is understood by `nsupdate`. See also the `-T` option.

-r udpretries

  The number of UDP retries. The default is 3. If zero, only one update request will be made.

-R randomdev

  Where to obtain randomness. If the operating system does not provide a `/dev/random` or equivalent device, the default source of randomness is keyboard input. `randomdev` specifies the name of a character device or file containing random data to be used instead of the default. The special value `keyboard` indicates that keyboard input should be used. This option may be specified multiple times.

-t timeout

  The maximum time an update request can take before it is aborted. The default is 300 seconds. Zero can be used to disable the timeout.

-T

  Print the list of IANA standard resource record types whose format is understood by `nsupdate`. `nsupdate` will exit after the lists are printed. The `-T` option can be combined with the `-P` option.

  Other types can be entered using "TYPEXXXXX" where "XXXXX" is the decimal value of the type with no leading zeros. The rdata, if present, will be parsed using the UNKNOWN rdata format, (<backslash> <hash> <space> <length> <space> <hexstring>).

-u udptimeout

  The UDP retry interval. The default is 3 seconds. If zero, the interval will be computed from the timeout interval and number of UDP retries.

-v

  Use TCP even for small update requests. By default, `nsupdate` uses UDP to send update requests to the name server unless they are too large to fit in a UDP request in which case TCP will be used. TCP may be preferable when a batch of update requests is made.

-V

  Print the version number and exit.

-y hmac:keyname:secret

  Literal TSIG authentication key. keyname is the name of the key, and secret is the base64 encoded shared secret. hmac is the name of the key algorithm; valid choices are `hmac-md5`, `hmac-sha1`, `hmac-sha224`, `hmac-sha256`, `hmac-sha384`, or `hmac-sha512`. If hmac is not specified, the default is `hmac-md5` or if MD5 was disabled `hmac-sha256`.

  NOTE: 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 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 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 (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

  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 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.

`ttl` seconds

  Specify the default time to live for records to be added. The value none will clear the default ttl.

`key` hmac: keyname secret

  Specifies that all updates are to be TSIG-signed using the keyname secret pair. If hmac is specified, then it sets the signing algorithm in use; the default is `hmac-md5` or if MD5 was disabled `hmac-sha256`. The `key` command overrides any key specified on the command line via `-y` or `-k`.

`gsstsig`

  Use GSS-TSIG to sign the updated. This is equivalent to specifying `-g` on the command line.

`oldgsstsig`

  Use the Windows 2000 version of GSS-TSIG to sign the updated. This is equivalent to specifying `-o` on the command line.

`realm` realm_name

  When using GSS-TSIG use realm_name rather than the default realm in `krb5.conf`. If no realm is specified the saved realm is cleared.

`check-names` yes_or_no

  Turn on or off check-names processing on records to be added. Check-names has no effect on prerequisites or records to be deleted. By default check-names processing is on. If check-names processing fails the record will not be added to the UPDATE message.

`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 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.

`answer`

  Displays the answer.

`debug`

  Turn on debugging.

`version`

  Print version number.

`help`

  Print a list of commands.

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
    > send

Any A records for oldhost.example.com are deleted. And 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 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 RRSIG, DNSKEY and NSEC records.)

## FILES

`/etc/resolv.conf`

  used to identify default name server

`/var/run/named/session.key`

  sets the default TSIG key for use in local-only mode

`K{name}.+157.+{random}.key`

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

`K{name}.+157.+{random}.private`

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

## SEE ALSO

RFC 2136, RFC 3007, RFC 2104, RFC 2845, RFC 1034, RFC 2535, RFC 2931, named 8 , ddns-confgen 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.