Dynamic DNS or DDNS is a technique to update dynamic domains in the Domain Name System. The purpose is that a computer after changing its IP address automatically, quickly changes to the corresponding domain entry.
So your computer is always available at the same domain name, even if the current IP address for the user is unknown.
There are two different mechanisms:
Update over HTTP or HTTPS, popularized by providers such as DynDNS
Update on a system modeled on DNS message log , specified in RFC 2136 and used by the program nsupdate.
DDNS via HTTP
A typical use case for dynamic DNS over HTTP or HTTPS is the host of a home user who accesses the Internet through a dynamic IP address of the ISP.
If the user wishes to operate a game server or access via remote desktop on the computer from the outside, he would have to know the constantly changing IP address.
To update a DDNS entry in the name server of the operator, a client software can be installed on the computer, or a corresponding function to be used in the home router.
Once the client detects a change of the IP address, it transmits these via an HTTP or HTTPS interface to the provider. Authentication is done through username and password.
The implementation of a client is not very complicated , as the network protocol is simple and many software libraries for HTTP / HTTPS connections are available.
Constantly changing entries were not initially foreseen in the Domain Name System. To save network resources, DNS entries are cached. The lifetime of an entry is predetermined by the name server.
With dynamic DNS usually a time to live is used by a minute to short-term benefit from caching without obsolete entries over a longer period point to an incorrect IP address.