Duck DNS is a free dynamic DNS hosted on Amazon EC2.
To get it working is quite easy. Add a sub domain and update your current ip address to it.
In above screenshot, I created 51sec.duckdns.org as a DNS to point to my home network ISP ip.
On one of my home internal machines, just installed a client to update the ip on 51sec.duckdns.org this dns name dynamically. The DuckDNS settings is shown in below screenshot. Put into your sub domain name and token. After all done, just click ok button, then it will automatically update it every 5 minutes.