DDNS, dynamic DNS, or more specifically, a dynamic domain name system, is a service that maintains and translates domain names into dynamic IP addresses. Through such a service, you can access your computer or files in your home from anywhere in the world.
DDNS serves a similar purpose to DNS. DDNS allows ftp servers, or other services, to access these services by "calling" a domain name instead of the IP address that changes at regular intervals.
However, unlike DNS, which only works with static IPs, DDNS is designed to work with dynamic IPs, which are used in most home-based internet connections. So a DDNS service is ideal if you want to access your home network from another network.
How do these services work?
To use this type of service, you should initially choose one such as NO-IP, and then create an account. Depending on the service you choose, there will be detailed instructions on how to set up the service. Usually there are software programs that the user needs to download and install on his server. Also, in some of these services, it is possible to set up directly on the router, so you do not need to run the software.
The way the software works is simple. Once it is running, it constantly checks whether the public IP has changed, and when it becomes aware that it has changed, it communicates with the DDNS service, updating it and updating its records.
In this way, while there is an active connection, and as the program is running, it is certain that whoever calls the domain you have created will be routed to the right place.
DNS VS DDNS
The reason static addresses use DNS, not DDNS, is because their domain name does not need to be updated. Static IPs, unlike IP dynamics, do not change.
Why you may need a DDNS service
Using dynamic DNS is the ideal solution for you if you maintain a webserver in your home, if you want access to your computer files regardless of where you are, or for any other reason.