Although DNS changes propagate through networks relatively quickly, the distributed nature of DNS and the fact that it is not fully automated means that it may take several hours to distribute a DNS change. While this is adequate for a service that only changes its IP address infrequently, it can be a problem if your IP address changes more often. For example, if you are running a server on an ISP that assigns IP addresses via DHCP, your public IP address will likely change more frequently. This is where DDNS, which provides a means of rapidly updating DNS information, comes in handy.
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 the...