Figure out reliable and securely by use of consensus the public ip address
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Why use PublicIpChangeDetector?

Compared to shell scripts for figuring out the public IPv4 address PublicIpChangeDetector will
securely and more reliable detect the current public IPv4 address than using a single public ip service. It's more secure because it does not require to trust a single server and uses HTTPS for tamper protection. What makes PublicIpChangeDetector more secure is, that it requires consensus between two randomly selected public IPv4 address web services. Because of this it's not possible for a single public IPv4 address web service to fool the program incorrectly thinking the public ip address has been changed. And by using multiple public IPv4 address web services the current public IPv4 can still be discovered after some time even when one or more public IPv4 web services are down. PublicIpChangeDetector is written in C so it executes fast and efficiently.

How PublicIpChangeDetector detects public IPv4 address change?

PublicIpChangeDetector randomly selects a HTTPS public IPv4 address service from a list of known HTTPS public IPv4 address services for figuring out the public IPv4 address. It then compares the result with the previous result to detect if the public IPv4 address has changed. If change is detected from previous request, the change is confirmed with another randomly selected public IPv4 address HTTPS service so if one public IPv4 HTTPS service is lying, the lie is detected. If the public IPv4 address is valid and is different from last run the posthook command is executed with the new IPv4 address as first command line parameter.

Flowchart of PublicIpChangeDetector operations

A flowcharts of how PublicIpChangeDetector works: flowchart PublicIpChangeDetector

Compiling PublicIpChangeDetector from source

Install the required packages.

sudo apt-get install build-essential libcurl4-openssl-dev libsqlite3-dev git-core

Get the PublicIpChangeDetector sourcecode in the folder /opt/ with:

cd /opt/
git clone

Compile the program with:

cd PublicIpChangeDetector/

Use of PublicIpChangeDetector

To use PublicIpChangeDetector for check public IPv4 address change of a server and update the dynamic DNS entries with a bash script. Do the following:

  1. Run crontab -e to edit your crontab.
  2. Add the following line to run PublicIpChangeDetector every 10 minutes as current user.
*/10 * * * * /opt/PublicIpChangeDetector/publicipchangedetector --posthook "/bin/sh /opt/PublicIpChangeDetector/"

Edit the example bash script with your scripting for updating your dynamic DNS entries.

Questions and Answers

Why not just trust one good public IP service for updating the (Dynamic) DNS?

You could do that but you are putting a lot of trust on one public IP address service that could technically hijack your domain record that you are automatically updating. By using PublicIpChangeDetector you don't have to fully trust one public IP address service as lies or an errors from one public IP address service are spotted by using consensus with an other randomly selected public IP address service. This makes for example fooling your server on a dynamic public IPv4 address into thinking incorrectly it needs to update dynamic DNS records hardly impossible.

Why not ask my router for my public IP address?

Good question. Well technically you could get the public IPv4 address from your router. But sadly every router manufacturer has a different webinterface for providing this information via their webinterface. And often the information is secured by a login screen. PublicIpChangeDetector does not rely on the router and there fautures to provide the public IP address and because of this it just works for everyone where there is internet access.

What is the maximum downtime for my server could have if my public IP address changes?

It depends on how often you run the publicipchangedetector program for detecting your public ip change. Also note that if a public ip address service lies to you it will take an extra publicipchangedetector run longer. And if you are using PublicIpChangeDetector for DDNS then it also depends on how long the DNS entries that needs to change are cached by the DNS servers for the old DNS records to be removed from cache.

Should i run PublicIpChangeDetector as often as possible?

No, please be conservative on how often you run publicipchangedetector. Several public ip services are already serving a lot of requests. They don't like it you use too much bandwidth and they will ban/drop you or maybe send you a http error if you are making too many requests too quickly.

Does PublicIpChangeDetector makes two request on execution?

No, it only make 1 http request if previous public ip address from last run is known.

What about IPv6?

There is no need to support IPv6 as the server is given a internet routable IPv6 address from your router.

How do i get the current public IPv4 address from commandline?

Run publicipchangedetector with the -showip argument to always print the current public ip address.

What command-line arguments can i use?

Run publicipchangedetector with the -h command-line argument for help on all the possible command-line arguments to use.

Does PublicIpChangeDetector need root rights?

No, PublicIpChangeDetector can just run fine as a lower privilege user as long as it can read and write to the data.db sqlite database file. Data.db stores all ipservice PublicIpChangeDetector can use and the information on the the last used ipservice. etc.

Are all the pubic ip service's hardcoded in the application?

All the services that are used are stored in a SQLite database file. If the SQLite database file exists you can remove, disable or add any public ip services with standard SQL. If the SQLite database file does not exist then the SQLite database file is created and about 20 public ip services are added to the database file by default to use.

Can i use the sourcecode in closed source software?

No, the GNU Public License forbids it. You can contact me as copyright holder and ask me to provide you with a close source version(non GPL) version for a small fee.


This project is free as in freedom, if you get it as free as in free beer depends on you. Beerpay Beerpay