What is Dynamic DNS?
Dynamic DNS, also referred to has DynDNS or just DDNS, is a method, that can update ressource records (RR) in the zone of a DNS. An example of this is updating the IP address of a hostname. DNS updates must be authenticated by a transaction signature (TSIG). The update is performed using a DNS update utility.
Where is DDNS used?
DDNS is a requirement, where a client needs to provide a service from a server or host, that does not have a static IP address from the ISP. DDNS is also a requirement, where a client has security devices, such as DVRs and IP security surveillance cameras, that can not be reached via a static IP address from the ISP.
Confirm connection to IP address.
Confirm, that the service can be reached via the currently assigned IP address from Internet. If the service is behind a router, the dashboard of the router will show the currently assigned IP address. If you are using a VPN service, you can not use the IP address from the VPN exit node. If necessary, you will also need to allow and map access from Internet via the router to the service on your LAN.
% ping 13.37.13.37
% ssh -p 1337 -l foobar 13.37.13.37
If the service is behind a 5G router, that is connected to a modern 5G network, that use carrier-grade NAT, also known as CG-NAT or just CGN, then you will not be able to reach the service via the assigned IP address from Internet. The reason is, that the assigned IP address is actually shared between other routers. In that case, DDNS is no longer a solution. You might want to use a VPN instead. This way, the client and server can connect to a VPN server on a VPS with a static IP address.
To be continued…