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
Copyright (c) 2013 - 2019 Frederik Lindenaar. free for distribution under the GNU License, see below
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 on how to setup the client side including:
In case you have any comments / questions or issues, please raise them through my GitLab instance 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.
Installation
The setup of this solution consists of the following steps:
- 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
Install the file
dyndns.pl
either in your cgi-bin directory or in a separate folderUpdate the configuration section at the top of the script to match your environment (see the section on 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.-
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 for an example of that.
-
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 theinclude
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 updatesite.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 theallow-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
~~~
-
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]
- execute the command
-
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.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.
Configuration
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 so that modifying the script is no longer required.
Parameter | Description |
---|---|
$ConfigFile |
Enable/disable config file support, see below |
$DNSServer |
IP address of the DNS Server to send DNS update requests to |
@DNSDomain |
How to determine the host's domain name, see below |
$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
|
$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 |
$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.
Configuration File
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) |
$DeleteTXT |
delete_txt |
DynDNS cleared on |
$DNSServer |
dns_server |
192.168.1.1 |
@DNSDomain |
dns_domain |
?, !, 0 (see below) |
$DomainListKey |
domain_list_key |
off (domain list disabled) |
$ExpandCNAMEs |
expand_cnames |
1 (1 level, see below) |
$ExpireAfter |
expire_after |
1w (1 week, see below) |
$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.
DNS Zone (Domain Name) Selection
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.
CNAME Support
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.
Authentication Modes
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
Request Parameters
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!
Invoking the script
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 it becomes:
http://myserver.mydomain.tld/list?domain=mydomain.tld&debug=...
Which is how I use it.
Expiring Records
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:
-
mode
should be set toexpire
-
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.
Configure as Virtual Host
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>
Integration with devices
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 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 parametersip
/ipv4addr
andipv6
/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
Cisco Routers
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
and 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.
AVM Fritz!Box routers
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 andSERVER
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
- Update URL:
- Click 'Apply' to store and activate the DDNS registrations
Check this page 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.
Synology DSM (NAS)
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 andSERVER
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__
- Service Provider:
- 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
- Service Provider: select the name you have just added (
- 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.
License
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/.