@TP-Link This not really a solution when all 4G suppliers use CGNAT.

@TP-Link 

I am trying to get to the bottom of the problems that I am having with this on a MR600 4G router but there does seem to be one thing at least which may not be working correctly within the firmware.

This issue is the DDNS client, for which I have an account with No-IP which the router logs into successfully. However the IP address that gets sent to No-IP is NOT the same as the IP address which the router says is its public IP address. I do understand about CGNAT but I am puzzled why the IP address that the DDNS client sends to No-IP is not the same as the one reported on the Status page of the router.

Onto the rest of the issue which I think I understand, which is that if I try to connect to the IP address given by the router on its Status page I get a 403 Forbidden message. I assume that this is probably because the device I am connecting to at that IP address is not the router, simply because of CGNAT.

If I were getting to the router it should not be responding with such a message because I have Remote Management enabled (assuming this works!). I therefore think the most likely explanation is that CGNAT is causing the IP address to be translated without the knowledge of the router, and the connection is therefore going to some other random device rather than to the router.

Finally, is there any prospect that the DDNS client will also implement PCP to punch a route through the CGNAT - what I don't know is whether the carrier needs to do anything so that the PCP transaction isn't simply discarded?

@TP-Link Most (possibly All) mobile data providers “such as Three & EE” do not provide a static or public IP.  Their mobile networks use Carrier Grade NAT (CGNAT) resulting in a double NAT, which means that you don't get your own public IP address but share it with other users. So, you can't be uniquely identified on the Net & therefore your LAN cannot be addressed from outside for unsolicited accesses.  You are provided with a private IP address on the mobile network.  This can't be used to remotely access the router or to port forward access to network devices.

Steve

@SteveF2 Thanks, yes, I do know about CG-NAT.

However I have now been told that Three uniquely do not use CGNAT if you use the an APN of "3internet". In this case your connection apparently bypasses CGNAT and has a public IP address. Whether this will continue is unknown and may possibly depend on how many IPv4 addresses Three can afford to use in this way. Given that it is not widely known about it is possible that this is not a big problem for them.

What I have been questioning is why the MR600 DDNS client is not reporting the IP address which the UI says is the "internet" address (on its status page) to No-IP. Where is it getting the IP address which it is sending?

My  speculation now after thinking about it is that this may be the actual public IP address the other side of the CGNAT translation, which it is picking up from the information fed to it when the connection is established. 

This would not, however, be enough to establish an inbound connection to my device because without a route to my device the packets will just go to (probably) port 80 at the public IP address, which will be blocked for obvious reasons. I can only imagine that this is the explanation.

I will be obtaining a Three data-only SIM shortly and will see whether it all works or not.

There are two things which it would be helpful to have in the DDNS client - firstly an indication of which IP address it will report, and secondly the ability to prompt a DDNS update. At present there is no indication of why and when the DDNS information gets reported to the server.

  @TP-Link Mmmm! "Not widely known about!"  That's the answer then??  I'll check that out.

Steve

  @TP-Link I am doing the same. My Three SIM is winging its way to me as we speak.

  @SuperFocus 

you have literally saved me on the back end of 8 hrs of troubleshooting. Couldn't connect to any Escape From Tarkov games AT ALL. I tried absolutely EVERYTHING. 
 

low and behold.

change APN to 3internet. I'm running an unlimited sim from Smarty which uses Three as a carrier,  £20/pm. Can confirm this 100% worked for me you legend!!! 

  @SuperFocus  Hi did any one get a solution to the TL-MR6400 router not being able to send its public IP address to the NO IP server. i have the seem problem and yet my router seem to hv the latest firmware v5.2.

I would wish to connect to my router remotely but apperantly i didnt have any success. Yet the DNS NO IP log in shows successful.

Any kind help i will be happy.