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So I've been looking into NAT traversing for my IoT project, and I'm a little confused. Here's how it goes:

When I go out to ask google "what is my public ip address?", I get an address like 46.114.190.96. This is, as far as I understand, my wifi router's IP address, since it serves as the public "portal" between my LAN and the public internet. Lets call this "the public IP".

The router also have a local IP address, 192.168.0.1, which I can use to log in to my router and do some settings. I'm setting up Virtual Server (for port forwarding, as I'd like to access my home server from outside the LAN). I've set it up so that it forwards traffic coming in to my local server, which for testing I hosted a simple web page. So far so good.

Things get confusing when I actually try to access the server, from outside the home network. If I type in 46.114.190.96, the page doesn't load. I've set the ports and everything up correctly.

BUT when I log into my wifi router, on the landing page it gives me another IP: 10.114.160.96. Lets call this one the "router IP"

and when I type this address in, voila, the page loads.

Even weirder, some of my friends typed the "router IP" in and can also access the page, and some other friends cannot (their browser just keeps trying to load until timeout). I've checked that the "router IP" is still the same. It does change once every now and then though.

So my question is:

  • What exactly is that "router IP"?

  • Why does it works for some of my friends, but doesn't for others?

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    the router IP should be visible in the router management webpage
    – jsotola
    Nov 8, 2022 at 20:49
  • your second question is not answerable here
    – jsotola
    Nov 8, 2022 at 20:49
  • Then what is the public ip that i got from google? I thought my router has a public ip and a local ip only, but here I'm given 3 ip addresses. Nov 8, 2022 at 21:39
  • These are network management questions and have nothing to do with IoT.
    – romkey
    Nov 8, 2022 at 22:44
  • there are websites that list the owners of IP addresses
    – jsotola
    Nov 9, 2022 at 1:34

1 Answer 1

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This sounds like your ISP is operating CGNAT (Carrier Grad Network Address Translation).

Most home networks normally operate with NAT (Network Address Translation) which means that all the devices on the home network get given an IP address out of a RFC1918 address range (in this case 192.168.0.x) and then the router will remap this to the external IP address given your router by the ISP. This IP address may change over time (usually does unless you are paying for a static IP address), but if you know this external address you can setup port forwarding and access devices inside your network.

Now when an ISP deploys CGNAT they no longer hand out a publicly routed IP address to your router, but they treat all the routers on their network like a home LAN and given them an address again out of the RFC1918 ranges (in this case a 10.x.x.x address, but they probably should be using 100.64.x.x-100.127.x.x) and then do translation to a much smaller range of public IP addresses at the edge of their network.

This basically means that the ISP can VASTLY reduce the number of publicly routeable IP addresses they need (which are very expensive now the only way to get them is to buy them from existing owners rather than getting them assigned from RIPE).

But it also means that you won't be able to use port forwarding, because it would need to be setup on both your router and the ISPs edge router (which isn't going to happen).

Your choices are as follows:

  1. Move to a new ISP that isn't using CGNAT (this will get harder and harder to do)
  2. Use something like ngrok to setup an outbound tunnel that can be used to access servers
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  • Some ISPs using CGNAT by default will allow users to be a public (and usually static) IP address. Some will do that for free (you just have to ask), others will require additional fees for that.
    – jcaron
    Nov 9, 2022 at 14:13

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