Normally my work involves offices with fixed IP addresses. Recently I have been working with an office that has a dynamic IP address that can change. It does not change often, but anytime the router restarts it may come back online with a new address.

That is really a pain if you have security that is managed by IP address. Without a site to site VPN to process traffic you can find yourself updating firewall rules often; which is not much fun.

I found that both pfSense and csf can accept FQDN (fully qualified domain names) for granting permissions through the firewalls. So if you have a dynamic IP address, but use a dynamic name resolution service you can grant permissions that will follow your IP address changes.

Hopefully you find a use for this, it really has made my life much easier.