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 that the process of updating DNS records is not fully automated, in many cases, it might take several hours for a DNS change to take effect. This may be a problem if the IP address associated with a domain name changes frequently. Consider, for example, a situation in which you are running a server (assuming your ISP allows this), and your ISP assigns your public IP address via DHCP. Perhaps your ISP does not give you the option of paying for a static public IP address, or perhaps you decided the cost of such an address was prohibitive. Whatever the case may be, your IP address is likely to change more frequently than it would otherwise, making traditional DNS undesirable. What you need is a means of rapidly (and if possible, automatically) updating DNS information. DDNS provides us with such a means.

DDNS actually refers to two separate services. The first involves using a client to push the DNS change out to a remote DNS server. The second involves updating traditional DNS records without manually editing them (this mechanism is specified by the IETF's RFC 2136). pfSense provides you with the ability to configure clients for use with both services, and we will cover both of them.