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I noticed my TP-Link MR3220 3G/WiFi Router port forwarding will only work when I use the WAN port and not the 3G connection (modem).

Technically the router offers an option to use the internet from 3G, WAN or both (given a priority). In my case I am only using in 3G and apparently, the router features such as Remote management and port forwarding don't work on this interface.

Anybody can confirm that? Is there any workaround (static routing or something)?

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It's most likely not the router, it's the 3G network. The traffic is never getting to the network because the 3G network has no idea how to route it. –  David Schwartz Mar 7 '12 at 7:44
    
I did not understand your comment. Once my router uses my 3G modem to connect to the Internet, I get a specific IP address. You mean the 3G provider won't route packages (such as ping) to this IP address? –  Jonas Mar 7 '12 at 18:07
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Yes, that's exactly right. In fact, the IP address you "get" may not even be unique to your device. –  David Schwartz Mar 7 '12 at 22:30
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5 Answers

All the 3G usb modems connect to a PPP server and it obtains its own IP address from the PPP server. The IP assigned to your TP-Link modem it the local IP provided by the USB modem. So even we have a unique public IP we cannot forward the incoming connections as we are not able to configure the USB modem.

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With the TP-Link MR3220 I was able to port forward on a Verizon 4G device (with a static IP). On the router you need to change the remote management interface port to a port other than a port you're trying to forward. So if you're trying to forward port 80 you need to change the remote management interface to another port, like 81.

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Many 3G service providers do not allow you to host servers on their connection. The problem in the case above is not the router but the 3G connection.

In Malaysia of the 3G service providers only MAXIS (ISP) allows incoming connections (hosting servers) the rest do not allow it.

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up vote 2 down vote accepted

Even though you get a real IP (which you can ping from any computer on the internet), it won't be possible to forward incoming connections.

Apparently all Mobile Internet Service Providers (ISP) block any kind of incoming connections. So, no matter which port I want to forward it will be blocked by the ISP. (connection requests will never reach the router).

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This isn't 100% accurate. The problem lies on what address you are given, most of the time it's already a NATed IP. However, many carriers can switch you to a real "external" IP - which is generally used for VPN because sometimes NAT can interfere with VPN (assuming you can get past the CSRs). However, even though this would be a publicly addressable IP - I imagine that they would still put in restrictions/firewall to prevent you from doing exactly what you are trying to do. –  Nathan Adams Oct 2 '12 at 4:28
    
So, for a commom end user, there is no chance I could run a server behind this kind of connection - because of the carrier's network topology and/or policy. –  Jonas Oct 2 '12 at 12:57
    
Policy - yes, network infrastructure...well there is a workaround for everything. In this case if you were deadset on serving something from your phone you could have a reverse SSH tunnel (or some sort of similar proxy) but this would require you to have a box that is accessible via the internet. Basically all the communication would go to that box then forwarded to your phone. I imagine it's against any carriers TOS, but if you have something that is low traffic - they probably wouldn't care. –  Nathan Adams Oct 2 '12 at 19:13
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If you make your 3G USB modem take a static IP, you can do this.

Remote management: From Security » Remote Management » In the remote management IP, enter 255.255.255.255 and a private port for you.

When you want to log in remotely to the 3G router from the internet, type for example http://212.196.8.13:8080 and it will prompt you for username and password for the router (if any).

Port forwarding: From Forwarding » Virtual Servers, type the port and the IP for which you want to forward, and this will work.

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I know how to setup remote management and port forward. The point of the question is why it won't work when connected on the internet through 3G interface and will work when connected through WAN interface. Plus I don't need static IP because I'm using the router's DDNS service (and it is working correctly). –  Jonas Mar 7 '12 at 18:04
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