# dyndns - simple dynamic DNS Update the given dynamic DNS A record remotely.

A remote HTTP(S) URI is used to determine the public IP address of the host. A crypto key is used to secure the communication with the DNS server that hosts the DNS zone to update.

• author: Didier Barvaux
• homepage: https://github.com/didier-barvaux/dyndns
• license: Simplified BSD License (see COPYING)

Features

• support Bind nsupdate
• support secure updates
• lightweight (no daemon, only shell script and a cron task)

Installation

Installation at DNS server

Create a new DNS zone within bind:

# cd /etc/named/dyn/
# touch dyn.example.com.zone
# chgrp named dyn.example.com.zone
# chmod g+w dyn.example.com.zone
# vim dyn.example.com.zone

Copy/paste the following content:

$ORIGIN .
$TTL 10 ; 10 seconds
dyn.example.com         IN SOA  ns1.example.com. root.example.com. (
                                1          ; serial
                                14400      ; refresh (4 hours)
                                3600       ; retry (1 hour)
                                604800     ; expire (1 week)
                                10         ; minimum (10 seconds)
                                )
$TTL 3600       ; 1 hour
                        NS      ns1.example.com.
                        NS      ns2.example.com.
                        MX      1 mail.example.com.

$ORIGIN dyn.example.com.
$TTL 600        ; 10 minutes

Create a crypto key:

# cd /etc/named/
# dnssec-keygen -b 512 -a HMAC-SHA512 -v 2 -n HOST dyn.example.com.

You should now have 2 new files in the current directory:

Kdyn.example.com.+xxx+yyyyy.key
Kdyn.example.com.+xxx+yyyyy.private

Configure bind with the new zone and the capacity to update the zone with the crypto key:

# cd /etc/named/
# awk '$1 == "Key:" { print $2 }' Kdyn.example.com.+xxx+yyyyy.private
(copy/paste the printed line at next step)
# vim /etc/named/named.conf 

Add the following content:

key dyn.example.com. {
	algorithm "HMAC-SHA512";
	secret "<secret key here>";
};

zone "dyn.example.com" IN {
   type master;
   file "dyn/dyn.example.com.zone";
   allow-query { any; };
   update-policy {
      grant dyn.example.com. name myfirsthost.dyn.example.com. A;
      grant dyn.example.com. name my2ndhost.dyn.example.com. A;
   };
   notify yes;
};

Then reload bind configuration:

# /etc/init.d/named reload

Installation on the dynamic host(s)

Build the man page as normal user: make all

Then install as root: make install PREFIX=/usr

It requires help2man, bash, curl, logger, awk, grep, nsupdate, and mktemp.

Then copy the content of the 2 Kdyn.example.com.+xxx+yyyyy.{key,private} files on the host:

# mkdir /etc/dyndns/
# touch /etc/dyndns/Kdyn.example.com.+xxx+yyyyy.{key,private}
# chgrp -R nobody /etc/dyndns/
# chmod -R o-rwx,g-w /etc/dyndns/
# vim /etc/dyndns/Kdyn.example.com.+xxx+yyyyy.key
(copy/paste content)
# vim /etc/dyndns/Kdyn.example.com.+xxx+yyyyy.private
(copy/paste content)

Uninstall

Uninstallation at DNS server

# rm -f /etc/named/dyn/dyn.example.com.zone
# rm -f /etc/named/Kdyn.example.com.+xxx+yyyyy.{key,private}
# vim /etc/named/named.conf
(remove the key dyn.example.com. and zone "dyn.example.com" blocks)
# /etc/init.d/named reload

Uninstallation on the dynamic host(s)

Just run make uninstall PREFIX=/usr.

If you want, remove the crypto key too:

# rm -rf /etc/dyndns/

Usage

Run manually:

# runuser -u nobody /usr/bin/dyndns https://example.com/checkip.php /etc/dyndns/Kdyn.example.com.+xxx+yyyyy.key ns1.example.com dyn.example.com myfirsthost.dyn.example.com.

Use cron to update the host's IP address periodically:

# vim /etc/crontab

then add the line below to update the DNS entry every 15 minutes:

*/15 * * * * nobody  /usr/bin/dyndns https://example.com/checkip.php /etc/dyndns/Kdyn.example.com.+xxx+yyyyy.key ns1.example.com dyn.example.com myfirsthost.dyn.example.com.