I have an ftp server which I wanted to access from outside of my local network. It is located on the IP port 21. I port forwarded port 21 and tried to connect with my phone while I wasn't connected to my wifi and it worked. The problem is I can't connect with any other device. Today I tried connecting with my phone again while I was away from home (so you don't think I was connected to wifi by acident) and it worked, but when my friend tried it didn't work. My network set up is: main ZTE router that is connected to the internet, TP-Link archer C7 which is connected to my ZTE router and I use it as an access point. My ftp server is also set up on Archer C7. I'm really confused with this problem because for some unknown reason it works for my phone but doesn't for everything else. Has anyone encountered anything like this?

P.S I contacted my ISP to ask them if they block my ports and they said they don't.

  • O)ne thing we can be sure: If it works for one device connecting from outside the network, it works. But what are you using from the phone? Just in case it's an app with some sort of "black magic" going on. – user772515 Apr 13 '18 at 20:04
  • I just open my regular chrome browser and go to the ip address and it works. – Nenad Apr 13 '18 at 20:13
  • When you try to access the FTP server in your browser, are you entering the IP address "" Because that should not work anywhere outside of your house. The whole 192.168.x.x block is reserved for private networks. So to access from outside your house you would have to enter the public IP address of your home router. And unless you pay your ISP extra money each month for a static IP address (usually very expensive and only used by businesses), your router's public IP address will change randomly at your ISP's discretion. So you probably want to use a hosting service or AWS... – A. Kendall Apr 13 '18 at 23:45
  • I am using my Public IP (10.215.*.*) when I'm connecting to it – Nenad Apr 14 '18 at 5:14
  • 10.x.x.x is not a public IP Address. – Tetsujin Apr 14 '18 at 7:14

Judging from comments, both your home connection and phone are on the Carrier-grade NAT system.

This is evident because your 'WAN' address is in the 10.* IPv4 range, which is private use (i.e. for NATs or isolated networks), so can't be reached by other machines on the internet.

Your phone can reach your home router because it is on the same NAT, in the same way that two machines on your home network can reach each other.


  1. Ask your ISP for a proper externally routable IPv4 address, but that may not be possible, or require extra money. Also ask for a static IP address so that you can reach your machine.
  2. Ask your ISP for an IPv6 address (range) - this is the correct long term solution since IPv6 has plenty of addresses available, but your ISP might not support it, and any clients will also need to have IPv6 addresses to reach you (or a gateway of some sort).
  3. Host your service on AWS or similar cloud providers.
  4. Ask for a tunnel in the Carrier grade NAT, but your ISP is unlikely to offer that.

Also ftp is probably not the best sort of server to set, they tend to have port problems, and ftp is unencrypted, it might be best to setup a sftp or http server instead?

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