Although DNS changes circulate through networks relatively quickly, the fact that it is not fully automated, and owing to the distributed nature of DNS, means that it may take several hours to distribute a DNS change. While this is enough for a service that only changes its IP address rarely, it can be an issue if your IP address changes more often. For instance, your public IP address will likely change more frequently if you are running a server on an ISP that assigns IP addresses via DHCP. This is where DDNS comes in handy, which is a way of rapidly updating DNS information.
DNS changes take place relatively quickly, and the amount of time it takes for changes to propagate to all DNS servers has improved drastically. Whereas in the past it may have taken days, now a DNS change might take effect in as little as an hour. Still, due to the number of DNS servers and the fact...