[SOLVED] Do DDNS Services Work Through CGNAT?

[Boris_yo]

Hi,

I can't configure DDNS from NO IP to work with my IP address. I think my cable modem's IP is static but it is never shown on websites that show your IP. The IP I see is very different there and it is dynamic.

I read on Reddit mixed opinions. Some say DDNS works thtough NAT, others say that it doesn't.

 

[bill001g]

The purpose of DDNS is to register your public IP to some name. When you do not actually have a public IP being assigned to your router it servers no purpose. So very technically you can get DDNS to assign some name to the shared public IP address you are using when there is NAT in the path but I can't see what benefit it provides.
The only reason to use DDNS is to keep track of what public IP is being assigned to your router. If you do not have a public IP to start with then none of the rest really matters.

 

[Boris_yo]

@bill001g With it I can use NextDNS service in full configuration because it requires linked IP that is up to date. I can also connect through internet to my home smart devices like camera and control it in real time, connect to my computer, watch videos, access photos. Assuming I can still port-forward...

 

[bill001g]

You miss the main point.

You must first have a public IP address.

Without that nothing else matters. If there is any form of NAT between you and your router you do not have a public IP address.

 

[Boris_yo]

So very technically you can get DDNS to assign some name to the shared public IP address you are using when there is NAT in the path but I can't see what benefit it provides.

Does that mean CGNAT and public IP assigned to cable modem can both exist at the same time? My understanding of CGNAT is to translate private IP of cable modem to public IP.

 

[bill001g]

That is what it does it translates the private IP to a public IP. BUT the private IP of many cable modems is being translated into the same public IP. The reason they use CGNAT is they do not have enough public IP to assign to everyone.

This means you would have to put port forwarding rules in the ISP router which will never be allowed.

Because you can never get a incoming session though a NAT router you do not control any form of DDNS is pointless.

 

[Boris_yo]

This means you would have to put port forwarding rules in the ISP router which will never be allowed.

I see. My DDNS dashboard at NO IP gets successfully updated but with cable modem's private IP (I believe it's static). Is port forwarding required for that IP to be forwarded through CGNAT and be seen as public IP in my dashboard?

 

[bill001g]

Yes there would need to be port forwarding rules in the ISP router. The ISP will never do that so it really doesn't matter.