The Dynamic DNS client built into pfSense® software registers the IP address of a WAN interface with a variety of dynamic DNS service providers. This is used to remotely access services on hosts that have WANs with dynamic IP addresses, most commonly VPNs, web servers, and so on.
Any number of Dynamic DNS clients may be configured using any of over 20 different Dynamic DNS providers, or even custom Dynamic DNS providers. Dynamic DNS clients can use any WAN, and can even register the real public IP address in environments where the firewall receives a private IP address for its WAN and is NATed upstream.
In addition to the typical HTTP/HTTPS-based Dynamic DNS providers, pfSense also supports RFC 2136 style Dynamic DNS updates directly to DNS servers.