Dns redirection not work

being given that I can not make request on local ip address, I made ​​it on a public ip address.
it works
However, the public IP address changes every 72 hours
I thought using a dns address but it does not work …
how should he do

You both need an address, could be from dyn.com, and then a web server running to relay the incoming requests to your local device. Remember to also open port 80 in the router and route it to the internal web server IP. Or have the internal device exposed (not something I would do if it was just a little slow arduino)

my dnsdyns works

In an http request in the agent code
public IP address works but not the dyndns

Then something is wrong with the dyndns, I am using one of my imps which also contacts a dyndns address, got no problems with that.