DNS which is know as Domain Name System which the record is key in manually and fix. When the DNS record is edited, it will always take 1-2 hours to fully resolved. By using the DNS, the server need to have a fixed IP. If you use the dynamic IP, the domain DNS record need to edit if the server dynamic IP is change to other dynamic IP. To address the issue of rapid change of dynamic IP (if the server is using the dynamic IP), Dynamic DNS might be the solution.
Dynamic Domain Name System or DDNS, is the solution if the server is using the dynamic IP. The basic idea is replace the IP by hostname, and the hostname A record will rapid change when the IP of that server is change. For the domain that use the DNS , the A record insert manually which normally use the fixed IP. The reason is because the A record will not change if there is no edit done. For the DDNS, the domain A record will change if the server IP is change. Here is the diagram.
To use the Dynamic DNS, the server need to install with DDNS agent and have the domain create on Dynamic DNS server. For example, the server.kcyeap.net is created on Dynamic DNS server, and it setup on web server as the hostname. The web server is installed with DDNS client and server.ihatetheory.com is configure as DDNS hostname. The DDNS client on web server will auto check the server IP and update to DDNS server for the latest server IP. When internet user use the server.kcyeap.net, it will auto check with DDNS server for the latest IP and connect to the correct IP.
The advantage for using the Dynamic IP is cost saving , where it was difficult/expensive to obtain a static IP. Other then that , by using the dynamic DNS is efficient where it do not need to configure again if there is any IP changes. With this NO-IP service, server admin can access the server by hostname and not to remember the number.