I have 3 ISPs(Internet service provider).
I’m from Argentina
One of them is TELECENTRO.
The other 2 are different PERSONAL (is an ISP from here) plans.
To open the router ports you have to do “port forwarding”.
TELECENTRO has CG-NAT, you must contact the ISP and ask them to disable it.
CG-NAT is used to avoid using so many public IPv4 IPs and to prevent them from running out.
There is IPV6 and a lot of it, but they resist change, which is why IPV4 is currently used.
A router works with a system called NAT.
CG-NAT is a technique used by the ISP, it must be disabled to open ports on the router.
Do not confuse CG-NAT with double NAT.
Double NAT is when you have two routers.
PERSONAL does not have CGNAT, you can do “port forwarding” directly
That is to redirect a port on the router to a port on a device that is connected to that router.
This is so that you can communicate remotely with another PC from the Internet using its public IP or router IP and external port or router port.
Those packets sent to the router’s IP and router port will be sent to a device you choose from the local network created by the router and internal port or device port.
To configure the router you must be on a PC connected to the router’s local network.
In this case, I will redirect the router traffic on port 51000 to port 52000 of a PC connected to my router’s local network.
On the PC you must access a web browser and enter the URL 192.168.0.1 or 192.168.1.1. This is to access the router’s web configuration interface.
You must look for a section that says “port forwarding” in English and configure it.
You must use a tool like netcat or nc to listen to a port on the device for port forwarding to work.
nc -l -k 52000- nc: Starts the Netcat tool.
- -l: Tells Netcat to go into “listening” mode, waiting for incoming connections.
- -k: With this option, you tell Netcat to remain in listening mode, even after a client has disconnected.
- 52000 is the port of the router or external port.
- By adding the -k option, you make your Netcat act as a simple daemon.
nc -l -k :portTo check that a port is open given a public IP, you can use an online tool called port checker.
https://portchecker.co/check-v0
You must first listen to a port on the device with NC
If you are not listening to the internal port you port fowarding to, the external port will be “closed”.
With the online port checker tool, verify that the external port says open.
image that says the port is “closed”, this is if you are not listening to the internal port to which you did “port forwarding” or if you have CG-NAT from your ISP.
If it says open, ready, you can communicate to the device and internal port from the public IP or router IP and external port if you do not have CG-NAT or double-NAT and if you did “port forwarding”