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how does it possible that applications in a cellular network are using the outside servers resources.but if you run for example a simple web server other's cannot see your web pages through the public ip address. it's interesting that it is possible to implement this scenario in an ADSL network.

what is the magic behind this ADSL?

i mean they are both providing you a public ip address

some guys says that your ISP block incomming traffic.i don't know what the hell this answer is.if your incomming traffic is blocked so you can't receive any data from any port of any ip in the internet, but i'm downloading and uploading and surfing the web for god sake.

aidin jalalvandi
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    ADSL routers normally allow port forwarding which lets traffic in to internal servers. Most mobile networks use Carrier Grade Nat which does not allow port forwarding. – DavidPostill Feb 13 '20 at 22:04
  • @DavidPostill so how am i using the internet? if they don't forward the packets from internet to NAT network how does it possible to for me to visit pages over internet from my Nat network? i mean i'm requesting a web page. that web page will respond to me and finally i should get this respond somehow. – aidin jalalvandi Feb 13 '20 at 22:08
  • The difference is you are accessing external servers not running your own server (on your phone). – DavidPostill Feb 13 '20 at 22:13
  • @DavidPostill well , i'm accessing external servers for sure, but the external servers will send the response to me for sure too, so i have a browser with opened port 45678 for example, this is looks like a server for me too which is listening in port 45678 and waiting for a connection. – aidin jalalvandi Feb 13 '20 at 22:18
  • Your browser is a client not a server. Please go and read up on this stuff, it's all basic knowledge that you need to have before you can ask a proper question. – DavidPostill Feb 13 '20 at 22:19
  • @DavidPostill i was thinking about it :) but i still don't figure it out. an open port is an open port.i'm receiving some data from these ports.but i can't host from these ports? how is it possible?this is my last question – aidin jalalvandi Feb 13 '20 at 22:23
  • [router - What is port forwarding and what is it used for? - Super User](https://superuser.com/questions/284051/what-is-port-forwarding-and-what-is-it-used-for) – DavidPostill Feb 13 '20 at 22:28

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There's a difference between connections that start outside of your network and connections that start inside of your network.

NAT, and carrier-grade NAT, will allow connections that start from the inside of the network. They will not allow connections that start from outside of the network unless you setup port forwarding.

NAT hides your IP address from the outside, and the IP you have is a "private" IP that is reused on many networks. One very common private range is 10.0.0.0 through 10.255.255.255. There's many, many private networks that use this, so something on the outside can't just send traffic to say, 10.0.0.1 and reach your device or any other. It has to talk to the router with a public IP, and that router has to use NAT to translate the incoming port to your private IP.

So there's no way something from the outside can reach you.

This is why you can browse the Web from behind NAT, but can't connect to devices behind the NAT from outside of it.

Carrier-grade NAT means your carrier controls the port forwarding and they are unlikely to open a port for you.

LawrenceC
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