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README.md

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.

Version 1.0, latest version, documentation and bugtracker available on my GitLab instance

Introduction

This script provides a simple interface to allow Dynamic DNS updates for DNS zones. It is intended to be used for routers and (aDSL) modems to register their IP address by simply opening a URL (this is supported by many modern devices) but can also be used by end-users (either directly by using a client). Please bear in mind that this script suits my setup and still might have glitches, but so far turned out to be a quite stable solution for my needs and I use it in a production setup. In case you have any comments / questions or issues, please raise them through my GitLab instance so that all users benefit.

Setup

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 nowadays on all *nix platforms). This description covers the installation on Apache 2.4, which 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.

The setup of this solution consists of the following steps:

Ensure that the Perl modules CGI and Net::DNS are installed.
- on Debian/Ubunto linux this can be done by:
```
   sudo apt-get install libcgi-pm-perl libnet-dns-perl
```

 * or if you have cpan installed:

   ~~~
   cpan CGI Net::DNS
   ~~~

Install the file dyndns.pl either in your cgi-bin directory or in a separate folder
Update 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
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, comment out 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
     ~~~

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. (
                     2015051401 ; 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]`

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&key=......>
   to add/update a site and
 * <http://myserver.mydomain.tld/dyndns/delete?host=site.dyndns.mydomain.tld&user=siteuser&key=......>
   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.

Parameter	Description
`$DNSServer`	IP address of the DNS Server to send DNS update requests to
`$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.

Please note that the values must be correctly quoted, etc. not to break the script.

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	Show DDNS domain entries	`domain`**
view	Show DDNS hostname entry	`host`
update	Update/add a DDNS host	`host` + auth.*	`ipv4addr`, `ipv6addr`
delete	Remove DDNS registration	`host` + auth.*
expire	Expire registrations	`domain`** + auth.*

* Modes that change registrations 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

Parameters

The script supports 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. `$ExpandCNAMEs` levels deep
`ip`	alias / shortcut for `ipv4addr`
`ipv4addr`	The IPv4 address to register for the host (update mode only) *
`ipv6addr`	The IPv6 address to register for the host (update mode only) *
`user`	signer of the DNS Update, used for `AuthMode` remote and both
`key`	key to sign the DNS Update, used for `AuthMode` remote and both
`debug`	debug key, show debug information if this equals `$AllowDebugKey`

* in update mode, if ipv4addr or ipv6addr is not provided with the request, the CGI variable $REMOTE_ADDR (the client address), its value will be used instead as IPv4/IPv6 address.

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 purposes. Please note that the Perl CGI library sets $REMOTE_ADDR to 127.0.0.1 and that the output will always be the HTML-based 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=...

Which is how I use it.

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.

The solution scales reasonable well, although adding the keys to the nameserver configuration is still manual in my setup (but since it does not happen that often, it's no hassle). This setup has been tested against ISC Bind version 9.

License

This script, documentation and configration 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, documenatation 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/.