What Does Dynamic Domain Name System (DDNS) Mean?
Dynamic DNS (DDNS or DynDNS) is a mechanism by which the name server in the Domain Name System (DNS) is automatically updated with the custom domain name and the ever-changing IP addresses. The DNS method is helpful in the case of dynamic IP addresses, where the IP address is mapped to a custom domain that changes frequently. However, in the case of a static IP address mapped to a custom domain, DDNS is not required. In general, a dynamic IP address is provided to residential or small business users. Big enterprises generally use static IP with their domain names.
Techopedia Explains Dynamic Domain Name System (DDNS)
In the early days of DNS, databases were small and it was easy to manage them manually. However, when a domain database grows, it becomes difficult to manage and update globally. The DNS system and domain name registers are distributed in nature, so it could take hours to update. In this scenario, The DNS system is suitable for static IP addresses mapped with custom domains.
But problems arise when the IP address changes frequently. Dynamic DNS is introduced to address this issue of rapid IP changes. When a domain name is searched, a dynamic IP address mapped with that domain is returned. This dynamic IP is provided by the internet service provider. At a later point of time when that same domain is searched again, a different IP address could be returned, because the ISP may be provided a different IP address from the IP address pool. Here, the DDNS system updates the DNS database every time the IP changes, and always keeps it updated with the domain-IP mapping. That way the outside world can access the domain name all the time without worrying about the IP changes.