scripts / DynDNS

dyndns.pl
=========

Perl CGI-BIN script to handle Dynamic DNS updates through HTTP (e.g. from a

router), updating DNS records through secure DNS update statements to run your
own Dynamic DNS Service.

**Version 1.1**, latest version, documentation and bugtracker available on my

[GitLab instance](https://gitlab.lindenaar.net/scripts/dyndns)

Copyright (c) 2013 - 2019 Frederik Lindenaar. free for distribution under the

GNU License, see [below](#license)


Introduction
------------

`dyndns.pl` provides a simple interface to allow Dynamic DNS updates for DNS
zones through HTTP requests. It is intended  for routers and (aDSL) modems to
register their IP address by simply opening a URL (this is supported by most
modern devices) but can also be used by end-users (either directly by using a
client). The script itself uses DNS' `nsupdate` calls to perform the update.
With this script you can integrate devices not supporting `nsupdate` and
environments where the master DNS server is not publicly available. The script
suits my setup/and needs and still might have glitches, but turned out to be a
very stable solution the last 6 years on both Linux as well as MacOS.

Please [see below](#integration) on how to setup the client side including:
  * [Cisco Routers](#cisco_integration)
  * [AVM Fritz!Box routers](#fritzbox_integration)
  * [Synology DSM](#synology_integration) (NAS)

In case you have any comments / questions or issues, please raise them through
my [GitLab instance](https://gitlab.lindenaar.net/scripts/dyndns) so that other
users can benefit and respond. Please also use this to submit setup instructions
for other devices you have set up for inclusion in this document.


Setup of the server side
========================

This script is to be executed as CGI-BIN script by a web server. As it is

written in Perl, it requires that installed (which is pretty standard on \*nix
platforms). This description covers the installation on Apache 2.4 and should be
similar for other web servers, with ISC Bind v9. For performance reasons
consider using the Apache mod_perl module for highly a volatile domain.

<a name=installation>Installation</a>
-------------------------------------

The setup of this solution consists of the following steps:

  1. Ensure that the Perl modules CGI and Net::DNS are installed.

     * on Debian/Ubuntu linux this can be done with:

~~~

       sudo apt-get install libcgi-pm-perl libnet-dns-perl

~~~

     * or directly from CPAN (assuming that is installed):

~~~

       cpan CGI Net::DNS

~~~

  2. Install the file `dyndns.pl` either in your cgi-bin directory or in a
     separate folder

  3. Update the configuration section at the top of the script to match your
     environment (see the section on [configuration](#configuration) below).
     The least you need to change `$DNSServer` to point to your DNS server and
     you probably want to have a look at the `$AllowDebugKey` (useful for
     getting things started but you want to set this to 'off' in production.

  4. To have a nicer URL (or in case the script is not installed in the web
     server's cgi-bin directory) add the following line to your Apache virtual
     host configuration (replacing `[INSTALL_DIR]` with the install directory):

     ~~~

     ScriptAlias /dyndns   [INSTALL_DIR]/dyndns.pl

     ~~~

     in case you have installed the script in a non-standard folder, you will
     also need the following to make this work on Apache 2.4 (again replacing
     `[INSTALL_DIR]` with the install directory):

     ~~~

     <Directory [INSTALL_DIR]/>
           AllowOverride None
           Options +ExecCGI -MultiViews -Indexes
           Require all granted
     </Directory>

     ~~~

     reload apache with `/etc/init.d/apache reload` to make the script

     available at <http://myserver.mydomain.tld/dyndns>.

     It is also possible to run as a virtual host, [see below](#VirtualHost) for
     an example of that.

  5. To setup your Bind nameserver, either update `named.conf` direcly or create
     a separate file (e.g. `named.dyndns.conf` in the Bind configuration
     directory and include that in your setup with the `include` directive
     (e.g. `include "named.dyndns.conf";`). For a basic dynamic DNS setup a
     configuration like below is required:

     ~~~

     // Define the keys for DynDNS
     key "dyndns.mydomain.tld" {
         algorithm hmac-md5; secret "QdDJC7QVYmsCxgWoSAUmBg==";
     };

     key "siteuser" {
         algorithm hmac-md5; secret "R6Xkbn+FP85Hq3EDNmv+GQ==";
     };

     // Define the DDNS zone
     zone "dyndns.mydomain.tld" IN {
          type master;
          file "dyndns/db.dyndns.mydomain.tld";

          // enable this for list and expire support
          // allow-transfer { 192.168.0.2; };

          update-policy {
                 grant dyndns.mydomain.tld zonesub ANY;
                 grant siteuser name site.dyndns.mydomain.tld ANY;
          };
     };

     ~~~

     The above defines a domain zone file `dyndns/db.dyndns.mydomain.tld` with
     two signer/keys. *siteuser* only can update `site.dyndns.mydomain.tld`
     while *dyndns.mydomain.tld* can update all entries in the domain (intended
     for expiry). If you intend to use expiry or want to be able to retrieve a

     list of all entries, uncomment the `allow-transfer` statement and update

     the IP adres to that of your web server.

     To seed these entries with fresh keys), use the following
     commands and copy the generated keys into the config file.

       * to generate a new key *dyndns.mydomain.tld*:

         ~~~

         ddns-confgen -a hmac-md5 -k dyndns.mydomain.tld -z dyndns.mydomain.tld

         ~~~

       * generate the required configuration for *siteuser* (or any new user):

         ~~~

         ddns-confgen -a hmac-md5 -k siteuser -s site.dyndns.mydomain.tld

         ~~~

  6. Generate an initial zone file like the one below for the dyndns domain in
     the location specified in the config file above.

     ~~~

     $TTL 3600       ; 1 hour
     @               IN  SOA auth.dns.mydomain.tld. hostmaster.mydomain.tld. (

                         2019000001 ; serial

                         43200      ; refresh (12 hours)
                          3600      ; retry (1 hour)
                         86400      ; expire (24 hours)
                           900      ; minimum (15 minutes)
                     )
                     TXT   "Dynamic DNS zone for mydomain.tld"

     site            A       1.2.3.4

     ~~~

     Please note that Bind will rewrite this file and you need to be careful
     with it. Entries do not need to exist initially, as long as the signer/key
     has access to a hostname, the entry can be created (so the only thing
     required to setup a new host is to register a signer/key).

     If you do need to update the zone file to change entries, consider using
     the bind `nsupdate` command instead. If that is inconvenient, the following
     steps must be followed not to get our of sync with Bind's zone database
     (please note that when you have views this works slightly differently):
       * execute the command `rndc freeze [zone]`
       * edit the zone file for [zone]
       * execute the command `rndc unfreeze [zone]`

  7. Last step is to instruct bind to reload it's configuration (`rndc reload`)
     and test the setup. please see [below how to invoke the script](#invoking).

     URLs / checks to perform are:
     * <http://myserver.mydomain.tld/dyndns/list?domain=dyndns.mydomain.tld>
       to list the entries in the domain (requires zone transfer rights!)

     * <http://myserver.mydomain.tld/dyndns/update?host=site.dyndns.mydomain.tld&user=siteuser&secret=......>

       to add/update a site and

     * <http://myserver.mydomain.tld/dyndns/delete?host=site.dyndns.mydomain.tld&user=siteuser&secret=......>

       to delete (clear) it.

Please read the section below as well on the configuration and different modes
(operations) available.

<a name=configuration>Configuration</a>
---------------------------------------
At the top of the script is a "Configuration" section, which contains the

configurable options of the scripts. As of version 1.1 the script also supports
a [configuration file](#config_file) so that modifying the script is no longer
required.

Parameter        | Description

:----------------|:-------------------------------------------------------------
`$ConfigFile`    | Enable/disable config file support, [see below](config_file)

`$DNSServer`     | IP address of the DNS Server to send DNS update requests to

`@DNSDomain`     | How to determine the host's domain name, [see below](#conf_dnszone)
`$DomainListKey` | Secret required to use the list mode, set to '' to always enable and to 'off' to disable this mode
`$ExpandCNAMEs`  | Max. CNAME lookups for `$host` (0 to disable), [see below](#conf_cname)

`$AllowDebugKey` | Output debug log after result when `debug` parameter equals this value. Set to '' to always enable and to 'off' to disable debugging

`$AuthMode`      | Defines how to authenticate DNS update requests, [see below](#conf_auth)

`$StaticSigner`  | Static signer ID to be used for AuthMode `static` or `both`
`$StaticKey`     | Static signing key to be used for AuthMode `static` or `both`

`$RequireRR`     | Require an existing DNS record of this type to allow updates
`$ExpireAfter`   | Expire time for registrations in minutes, hours, weeks or seconds. Format is number optionally followed by m, h, w, s (seconds is default)

`@ReplaceRR`     | List of DNS Record types to remove (clear) as part of update.
`$UpdateTXT`     | Add host TXT record during update with this text followed by a timestamp. Used for expiry (so don't change!), leave empty to not add this

`$DeleteTXT`     | Set TXT record upon deletion with this text and a timestamp.
`$RecordTTL`     | TTL for created records in minutes, hours, weeks or seconds. Format is number optionally followed by m, h, w, s (seconds is default)

Please note: when changing the script all values must be correctly quoted, etc.
not to break the script. Therefore as of version 1.1 a config file is supported
(preferred), [see below](config_file).


#### <a name=config_file>Configuration File</a>
The script can read its settings from a config located in the same directory as
the script and with the extension `.cfg` (ignoring a `.pl` extension) so the
default config file would be `dyndns.cfg`. The behavior of how to support the
config file is configured through the variable `$ConfigFile` and can be one of:
  * `optional` - config file is read if it exists, this is the default
  * `required` - config file is read and must exist (or the script will fail)
  * `ignore` - config file is ignored and not read, configuration in the script

The general format of the config file is `keyword = value`, see the table below
for a mapping of the parameters to keywords. For lists (variables starting with
a `@`) the value is comma-separated. The config file supports comments, ignores
empty lines, starting/trailing spaces and everything following a `#`. Refer to
`dyndns.cfg.dist` for an example config file. Please note that the script will
fail if it encounters an error or unknown keyword in the config file.

Parameter         | Config Setting     | Default value
:-----------------|:-------------------|:------------------------------
`$AllowDebugKey`  | `allow_debug_key`  | `off` (debugging disabled)
`$AuthMode`       | `auth_mode`        | `remote` ([see below](#conf_auth))
`$DeleteTXT`      | `delete_txt`       | `DynDNS cleared on`
`$DNSServer`      | `dns_server`       | `192.168.1.1`
`@DNSDomain`      | `dns_domain`       | `?, !, 0` ([see below](#conf_dnszone))
`$DomainListKey`  | `domain_list_key`  | `off` (domain list disabled)
`$ExpandCNAMEs`   | `expand_cnames`    | `1` (1 level, [see below](#conf_cname))
`$ExpireAfter`    | `expire_after`     | `1w` (1 week, [see below](#expire))
`$RecordTTL`      | `record_ttl`       | `1h` (1 hour)
`$RequireRR`      | `require_rr`       |
`@ReplaceRR`      | `replace_rr`       | `A, AAAA, TXT`
`$StaticKey`      | `static_key`       |
`$StaticSigner`   | `static_signer`    |
`$UpdateTXT`      | `update_txt`       | `Last DynDNS update on`

Please note that since `$ConfigFile` determines config file support, it cannot
be configured in the file. By default the config file is optional not to break
existing configurations.


#### <a name=conf_dnszone>DNS Zone (Domain Name) Selection</a>
In order to send the right update request to the DNS server, the correct DNS
zone to update must be determined based on the request's hostname. Most of the
time an update for `hostname.subdomain.mydomain.tld` is an update of `hostname`
the DNS zone `subdomain.mydomain.tld` and then the defaults are sufficient.
However, in some scenarios (e.g. one of my use cases) an update should be sent
for hostname `hostname.subdomain` in the zone `mydomain.tld` instead. The DNS
server cannot figure this out itself (at least ISC's Bind9 can not) so it is
implemented here.

The array `@DNSDomain` contains a list of values matched against the hostname
to determine the DNS zone to update and can contain:

Value            | match hostname ending with
:----------------|:-------------------------------------------------------
`"?"`            | the domain name from parameter `domain`
`"!"`            | server name the HTTP(S) request was sent to
`0`              | domain from hostname (strip of everythin till first `.`)
positive number  | last # parts from hostname
negative number  | last # parts of server name the HTTP(S) request was sent to
any other string | use value specified

The first parameter matching the hostname's end will be used. The default is
`( '?', '!', 0 )`, which should be OK in most cases.


#### <a name=conf_cname>CNAME Support</a>

The script supports using separate subdomain (e.g. dyndns.mydomain.tld) for
dynamic DNS and CNAMEs to entries in that subdomain from another zone (e.g.
mydomain.tld). The advantage of such a setup is that only one zone (SOA file)
within the domain will have frequent updates (and hence requires a short TTL
so prevent it from being cached) while the rest of the domain's zones can be
cached.

The user does not have to notice this at all as script supports check whether
the host provided is a CNAME and if so, performs the request for the actual
hostname instead of the provided one. The value of `$ExpandCNAMEs` determines
the maximum number of CNAME lookups supported (so nesting is allowed and this
limits the level of nesting to prevent loops).

To disable lookups for CNAME expansion, set `$ExpandCNAMEs` to 0.

#### <a name=conf_auth>Authentication Modes</a>

For signing DNS update requests sent to the DNS server the script supports 3
ways to obtain the signer and key:

AuthMode | Description

:--------|:---------------------------------------------------------------------

*static* | use only static authentication information from `$StaticSigner` and`$StaticKey` (and ignore authentication information provided in the request)

*remote* | use only authentication information provided in the request

*both*   | use authentication information provided in the request (fields `user` and `secret`) when provided, otherwise use static values from `$StaticSigner` and `$StaticKey`. Please note that this is checked per parameter


Supported Operations
--------------------
The script can perform the following operations (modes):

Mode   | Description            | Required Parameters | Optional Parameters
:------|:-----------------------|:--------------------|:----------------------
list   | List zone __***__      | `secret` __***__    | `domain`__**__
view   | Show host's DNS entry  | `host`              |
update | Update/add a DDNS host | `host` + auth.__*__ | `ipv4addr`, `ipv6addr`
delete | Remove registration    | `host` + auth.__*__ |
expire | Expire registrations   | `domain`__**__ + auth.__*__

__*__   modes that change DNS require authentication, depending on the value of
        `$AuthMode` the parameters `user` and `secret` may be required

        (`$AuthMode` *remote*) required or optional (`$AuthMode` *both*)

__**__  in case `domain` is omitted, it will be determined using the `host`

        parameter, if provided, or by using the virtualhost the script runs on
        based on the `@DNSDomain` setting

__***__ list mode is only available when `$DomainListKey` is not set to `off`,
        in case `$DomainListKey` is not empty, `secret` is required and must
        equal the key in `$DomainListKey`


#### <a name=req_params>Request Parameters</a>
The script supports (requires) the following parameters (please see the table
above for which is needed for what mode):

Parameter  | Description
:----------|:-------------------------------------------------------------------
`mode`     | the action to perform (if not provided as part of the path name)
`domain`   | domain for list/expire request, determined from `host` if ommitted
`host`     | hostname to act on, expand CNAMEs max. `$ExpandCNAMEs` levels deep
`ip`       | alias / shortcut for `ipv4addr`
`ipv4addr` | The IPv4 address to register for the host (update mode only) __*__
`ipv6`     | alias / shortcut for `ipv6addr`
`ipv6addr` | The IPv6 address to register for the host (update mode only) __*__
`user`     | signer of the DNS Update, used for `AuthMode` *remote* and *both*
`secret`   | key to sign the DNS Update, used for `AuthMode` *remote* and *both*, also used as `$DomainListKey` for list mode.
`debug`    | debug key, show debug information if this equals `$AllowDebugKey`

__*__   in update mode, if `ipv4addr` or `ipv6addr` is set to `auto` in the

        request, the CGI variable `$REMOTE_ADDR` (the client address), its value

        will be used instead as IPv4/IPv6 address. __Please Note__ that if both
        are omitted existing addresses will be removed!

#### <a name=invoking>Invoking the script</a>

The script is implemented using the perl CGI module so for testing purposes it
can be called from the command line with parameters as arguments, i.e.

    ./dyndns.pl mode=expire domain=mydomain.tld debug=....

Which is quite handy for debugging. Please note that the Perl CGI library sets
`$REMOTE_ADDR` to 127.0.0.1, the server name in this case will be `localhost`
and that the output is the HTML result.

The standard way to use the script is to place it in the cgi-bin folder your
server, which allows it to be called as:

    http://myserver.mydomain.tld/cgi-bin/dyndns.pl?mode=list&domain=mydomain.tld&debug=...

As per the setup instruction above, there are various ways to make the URL
cleaner, i.e.

    http://myserver.mydomain.tld/dyndns?mode=list&domain=mydomain.tld&debug=...

The script also supports include the mode variable as part of the location
(using and the CGI variable `$PATH_INFO` to set the mode), i.e.

    http://myserver.mydomain.tld/cgi-bin/dyndns.pl/list?domain=mydomain.tld&debug=...

When combining the setup would become:

    http://myserver.mydomain.tld/dyndns/list?domain=mydomain.tld&debug=...

If using a dedicated virtual host [see below](#VirtualHost) it becomes:

    http://myserver.mydomain.tld/list?domain=mydomain.tld&debug=...

Which is how I use it.

### <a name=expire>Expiring Records</a>
The script can expire registrations after a while. For this, it must add a TXT
record containing the date of the last change (on by default) and when requested
it will remove any entry older than the value configured in `$ExpireAfter`.

Please note that:
  * as this is dependent on the value of a TXT record, it may fail if these
    records are updated through another method.
  * there is no security implemented (other than the value of `$ExpireAfter`)

To initiate the expiry, the script must be called with two parameters:
  1. `mode` should be set to `expire`
  2. `domain` must be set to the DNS Zone (domain) to run against.

Both can be setup easily in cron with entries like:

~~~
# Samples to run the expiry every hour

# Cron fields definition:
#.---------------- minute (0 - 59)
#| .------------- hour (0 - 23)
#| |  .---------- day of month (1 - 31)
#| |  |  .------- month (1 - 12) OR jan,feb,mar,apr ...
#| |  |  |  .---- day of week (0 - 6) (Sunday=0 or 7) OR sun,mon,tue,wed,thu,fri,sat
#| |  |  |  |
#* *  *  *  * user-name command to be executed

# Directly run the script, does not require specific permissions
15 *  *  *  * www-data  [INSTALL_DIR]/dyndns.pl mode=expire domain=mydomain.tld

# example using curl
15 *  *  *  * www-data  curl https://myserver.mydomain.tld/expire?domain=mydomain.tld > /dev/null
~~~

Name Server Setup Requirements
------------------------------
As the script is only translating requests, depends heavily on the setup of the
nameserver. The DNS server (obviously) needs to allow DNS updates. In addition

to the setup described above, please note that:

  * For the modes list and expire to work, the script needs to perform a DNS
    zone transfer (AXFR). This must be allowed for the host running the script.
  * for each DDNS host, a signer and key must have the rights to change the
    entry (one signer/key can be setup to change multiple hosts).
  * The expire mode requires a signer and key that can change all DDNS hosts
    within the domain.
  * The script currently only supports HMAC-MD5 type keys (limitation of the
    used Perl Net::DNS library). The keys setup in the nameservers must
    therefore be of the same time or authentication won't work.

This setup has been tested against ISC Bind version 9 and scales pretty well.
Adding the keys to the nameserver configuration is still manual in my setup but
bit difficult script, if needed.


<a name=VirtualHost>Configure as Virtual Host</a>
-------------------------------------------------
Running dyndns.pl on a Virtual Host is possible using `mod_rewrite`. This is how
I use it as it allows the URLs to become even more simple, e.g.:

  * to update: `https://dyndns.mydomain.tld/update/hostname.mydomain.tld?secret=...`
  * to delete: `https://dyndns.mydomain.tld/delete/hostname.mydomain.tld?secret=...`
  * to view:   `https://dyndns.mydomain.tld/view/hostname.mydomain.tld`
  * to list:   `https://dyndns.mydomain.tld/list/mydomain.tld?secret=...`
  * to expire: `https://dyndns.mydomain.tld/expire/mydomain.tld`

An example Apache 2.4 config is shown below (please replace `[INSTALL_DIR]` with
the install directory and obviously replace the server name as well):

~~~
<VirtualHost *:80 *:443>
  ServerName dyndns.mydomain.tld

  # Enable URL Rewriting
  RewriteEngine On

  # Enforce HTTPS access
  RewriteCond %{HTTPS} off
  RewriteRule /         https://%{HTTP_HOST}%{REQUEST_URI}      [R]

  # re-route everything to the dyndns script
  RewriteRule (.*)      /dyndns/$1                              [PT]

  ScriptAlias /dyndns           [INSTALL_DIR]/dyndns.pl

  <Directory [INSTALL_DIR]>
        AllowOverride None
        Options +ExecCGI -MultiViews
        Require all granted
  </Directory>

</VirtualHost>
~~~


<a name=integration>Integration with devices</a>
================================================
Integration on routers and other devices is straigtforward, provided do support
DDNS registrations using a custom URL. The Basic format for the registration
URL to register is:

~~~

https://SERVER/cgi-bin/dyndns/update?host=HOSTNAME&ip=IPADDRESS&secret=KEY

~~~

Check the [list of parameters supported](req_params) for all available options,
the above URL contains the absolute minimum where:

Parameter   | Value
:-----------|:---------------------------------------------------------------
`SERVER`    | is the host the script is installed on
`HOSTNAME`  | is the client's hostname as configured in the DNS server
`SECRET`    | is the secret key as configured in the DNS server
`IPADDRESS` | is the ipv4 address (often dynamic, can also be set to `auto`)

Depending on how you have configured the URL of the script to be, the path
(`/cgi-bin/dyndns/` may need to be altered as per your setup).

Please note that:
  * The generated secret may contain a `+`, which must be encoded correctly in
    the request or it will fail. I found that not all clients (e.g. a Fritz!Box)
    do this correctly, make sure that your secrets either don't contain a `+`
    or encode it manually (replace any `+` with `%2B` in that case).
  * In case the IP address of the device is behind NAT and you want to have the
    public address register, use the `auto` value for parameters `ip`/`ipv4addr`
    and `ipv6`/`ipv6addr` to have the script auto-detect it (though that this
    can only be used for either an IPv4 or an IPv6 address and will only work
    for devices registering using that protocol!)
  * Some devices have a preference to connect over IPv6 (e.g. Cisco routers).
    This can be used to register the IPv4 and IPv6 addresses together by passing
    the IPv4 address as parameter en setting the IPv6 parameter to `auto`.
  * Some devices (e.g. a Fritz!Box) support a separate URL for IPv4 and IPv6
    registrations. Unfortunately this script cannot handle this yet and will
    unregister a previous registration when the second request comes in. Please
    raise a ticket if you have such a situation to work on a solution together.

To check whether the client's registration was successful (and correct) visit:

~~~
https://SERVER/cgi-bin/dyndns/view?host
~~~


<a name=cisco_integration>Cisco Routers</a>
-------------------------------------------
For Cisco routers add the following config:

~~~

ip ddns update method DYNDNS
 HTTP
  add https://SERVER/cgi-bin/dyndns/update?host=<h>&ip=<a>&secret=SECRET
  remove https://SERVER/cgi-bin/dyndns/delete?host=<h>&secret=SECRET
 interval maximum 0 1 0 0

~~~

replacing `SERVER` for the host the script is installed on and `SECRET`
for a DNS key authorized to update the record. The cisco router will replace <a>
and <h> with the IPv4 address and hostname.

To setup interface `Dialer0` to register as `hostname.dyndns.mydomain.tld` add:

~~~

interface Dialer0
 ip ddns update hostname hostname.dyndns.mydomain.tld
 ip ddns update DYNDNS

~~~

Which instructs to register using the address of Dialer0 as soon as that is up
or changes (this also works for non-dialer devices).

Please note that before entering the `?` as part of the URL, a `CTRL`-`V` is
required to prevent the Cisco CLI to list the available command parameters.


<a name=fritzbox_integration>AVM Fritz!Box routers</a>
------------------------------------------------------
To setup DynDNS on a Fritz!Box perform the following steps:
  * Login to your Fritz!Box as an admin user
  * Open the 'Internet' menu an go through the 'External Access' page
  * Open the 'DynDNS' tab
  * Enable the 'Use DynDNS' checkbox
  * Select DynDNS Provider: 'User-defined'
  * Enter the following data (replacing `YOURDOMAIN` with your DynDNS domain
    and `SERVER` with your server name - check the rest of the URL as well!)
    - Update URL: `https://SERVER/cgi-bin/dyndns/update?host=<domain>&ip=<ipaddr>&secret=<pass>`
    - Domain name: hostname setup in DNS
    - Username/Email: put here something, not used unless you add it to the URL
    - Password: secret key setup in DNS
  * Click 'Apply' to store and activate the DDNS registrations

Check [this page](https://service.avm.de/help/en/FRITZ-Box-7581/017p2/hilfe_dyndns)
for the available parameters that can be substituted in the URL.

The status of the DynDNS registrations can be seen in the 'Internet' menu on the
'Online Monitor' page.

To stop DynDNS registrations, uncheck 'Use DynDNS' from the same screen.


<a name=synology_integration>Synology DSM (NAS)</a>
---------------------------------------------------
To setup DynDNS on a Synology NAS (DSM 6 or later) perform the following steps:
  * Login to your Synology NAS DSM as an admin user
  * Open the Control Panel and go to 'External Access'
  * Click 'Customize' to add a new DDNS provider
  * Enter the following data (replacing `YOURDOMAIN` with your DynDNS domain
    and `SERVER` with your server name - check the rest of the URL as well!)
    - Service Provider: `YOURDOMAIN`
    - Query URL `https://SERVER/cgi-bin/dyndns/update?host=__HOSTNAME__&ip=__MYIP__&secret=__PASSWORD__`
  * Click Save to store the custom DDNS provider
  * Click Add to register the DDNS registration and enter:
    - Service Provider: select the name you have just added (`*YOURDOMAIN`)
    - Hostname: hostname setup in DNS
    - Username/Email: put here something, not used unless you add it to the URL
    - Password/Key: secret key setup in DNS
  * Click 'OK' to store and activate the DDNS registrations

After a while the screen should display that the status is Normal and when the
last update occurred.

To stop DDNS registrations, 'Delete' the registration from the same screen.


<a name=license>License</a>
=============================
This script, documentation and configuration examples are free software: you can

redistribute and/or modify it under the terms of the GNU General Public License
as published by the Free Software Foundation, either version 3 of the License,
or (at your option) any later version.

This script, documentation and configuration examples are distributed in the

hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied
warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
General Public License for more details.

You should have received a copy of the GNU General Public License along with
this program.  If not, download it from <http://www.gnu.org/licenses/>.