nsd-dyndns

Introduction

nsd-dyndns is a simple script that adds dynamic DNS dunctionality to NSD (authoritative DNS name server).

Requirements

The following is required or suggested:

• OpenBSD (or another BSD or some Linux distro) with HTTPD and NSD installed (pkg_add nsd), configured and running
• (sub-)domain for your webserver. Needed for updating the NS record of your actual DynDNS domain.
  • In this example: update.example.com
• (sub-)domain that is updated dynamically.
  • In this example: dyn.example.com
• A router capable of sending custom GET-requests to your DynDNS server.
  • In this example: A FritzBox

Installation

Configure your web server

Apache/httpd

Add the following new virtual host to your /etc/httpd.conf:

server "update.example.com" {
        listen on $ext_addr port 80
        root "/htdocs/dyndns"
        log access dyndns.log
}

nginx

Add the following to your nginx.conf. The "access" log format isn't avaliable by default so you have to define it.

http {
    ...
    log_format access '$host $remote_addr - $remote_user [$time_local] '
                               '"$request" $status $body_bytes_sent '
                               '"$http_referer" "$http_user_agent" "$gzip_ratio"';
    ...

    server {
        listen 80;

        server_name update.example.com;

        root /htdocs/dyndns;
        access_log /var/www/logs/dyndns.log access;

        ...
    }
}

Create an empty update.html:

# mkdir /var/www/htdocs/dyndns/
# touch /var/www/htdocs/dyndns/update.html

After reloading webserver, try to access http://update.example.com/update.html The request should show up in /var/www/logs/dyndns.log

Create a zone file for dyn.example.com

Create a new zone file (e.g. at /var/nsd/zones/dyn.example.com.zone) with the following content

$ORIGIN example.com.
$TTL 300
@       IN      SOA     ns1.example.com.      admin.example.com. (
1524952218
                        300                     ; refresh
                        900                     ; retry
                        1209600                 ; expire
                        1800                    ; ttl
                        )
; Name servers
                    IN      NS      ns1.example.com.
                    IN      NS      ns2.example.com.

; A records
@ IN A 123.123.123.123
update IN A 123.123.123.123
dyn IN A 123.123.123.123

Don't forget to set your own domain names, name servers and ip addresses Furthermore, add this zone file to your /var/nsd/etc/nsd.conf

Configure and Install nsd-dyndns

• Copy dyndns.conf-dist to /etc/dyndns.conf
  • # cp dyndns.conf-dist /etc/dyndns.conf
• Edit /etc/dyndns.conf to your needs
• Copy dyndns.sh to /usr/local/bin/dyndns.sh
  • # cp dyndns.sh /usr/local/bin/dyndns.sh
• Make the script executable:
  • # chmod u+x /usr/local/bin/dyndns.sh
• Add /usr/local/bin/dyndns.sh to your crontab

Configure your router

Configure your router to query the following URL:

update.example.com/update.html?qwertzuiop1234567890

Don't forgert to set your own domain name and to replace the string after "?" with the password you configured in the config file.

What it does

When your router gets a new IP and therefore sends an HTTP request to your server, a similar entry should appear in your /var/www/logs/dyndns.log:

update.example.com 123.123.123.123 - - [29/Apr/2018:20:48:19 +0200] "GET /update.html?qwertzuiop1234567890 HTTP/1.1" 200 6

When the script is executed e.g. via cron, the following happens:

• It greps the last line of /var/www/logs/dyndns.log where the correct password was found and extracts the requesting IP address
• It checks if this IP is the same than the last time
• If it's a new IP, then it replaces the forth line in your zone file - the line with the version number - with a new version (current unix time stamp)
• As a second step, it updates the A record of you DynDNS domain (dyn.example.com in our example)
• It then stores the new IP in the file /tmp/last_dyndns_ip.txt
• Finally it reloads NSD