Networking newbie question:

I am trying to understand what would be the best way to expose several mobile web servers, all of them are behind a router which is a typical 3G network configuration, here all 3G mobile has only a private IP, so in this case we have several web servers all of them are unreachable.

If a have a DNS server can I use DNS A record to point to this web servers (no public IP) and a reverse proxy (d.example.com) to forward traffic to each mobile web servers?

The application that I am trying to do will make those web servers accesible (no public IP) using a subdomain of the proxy server for instance 3gwebserver.example.com

Is there a way to accomplish this?

  • Yes, sure. There is a way. The question remains: Why in gods name do you want that?
    – mailq
    Dec 5, 2011 at 23:20
  • I have several energy sensors, all of them have a web server to access to collected data. But these energy sensors are connected to internet using a GPRS link, for fast and temporal deployment, but I need to access from internet to collected data, but now I am not able access to this energy sensors because my Mobile data provider is not able to give public IP for all my sensors.
    – Jaime
    Dec 5, 2011 at 23:29
  • I don't get the downvotes - while it's a patently ludicrous scenario, the poster does ID himself as a newbie, and it is a question that someone might find useful later in a similarly bad use case scenario. Dec 5, 2011 at 23:32
  • +1 There are places in the world where it is easier (or cheaper) to use 3G connectivity instead of the "traditional" alternatives. Remote weather stations for example.
    – user62491
    Dec 6, 2011 at 1:19

3 Answers 3


Your main issue is this: You have a router/firewall out in front of your mobile device. Unless you have some way of accessing that ISP/phone company router to enable port forwarding, you'll never be able to access the webserver externally. Even if you hook up something like No-IP or DynDNS to your webserver so that the external IP address of the ISP/phone company is correct, without port forwarding those requests will just hit the firewall and stop.

Bottom line - your ISP/phone company would have to approve of this plan and let you do it or it's going to fail miserably...

EDIT As mailq points out in a comment - you need data pushing, not data pulling - you're almost certainly seeing your competitors pushing data automatically from the sensors to a central server. That's pretty easy to accomplish. Pulling data from behind the 3G NAT routing is dependent entirely on your 3G carrier participating with you.


If your 3G provider is giving you a private IP, then you're behind what's called Carrier Grade NAT.

You will need their involvement to get anything behind that network exposed for inbound connections.

There's nothing you can do from your end to get it working.

Just saw your comment. Are you able to get these sensors re-engineered so that they push the data to a central server, rather than having it fetched?

Also, depending on how powerful the devices are, get the devices to initiate a VPN may be an option as that abstracts away the carrier grade NAT.

  • Think of "push" than "pull".
    – mailq
    Dec 5, 2011 at 23:31
  • I know is possible because a have another energy sensors which connect to a proxy servers when ther are started and automatically the proxy servers add a subdomain to access to it. egauge.net/devices here you can access to all energy sensors and all of them are behind a Carrier Grade NAT.
    – Jaime
    Dec 5, 2011 at 23:32
  • Like mailq said - those devices are pushing data back to a central server, not having said server pull it. You can push over 3G as much as you want. Pulling is REALLY difficult. Dec 5, 2011 at 23:35
  • I bought yhose sensors from egauge.net, I am starting a energy management business based on those sensors and the embedded web server is very useful and its API to access and process its data too.
    – Jaime
    Dec 5, 2011 at 23:40
  • Others do research before buying stuff. What do you gain from a web interface you cannot access?
    – mailq
    Dec 5, 2011 at 23:49

The fastest (not cheapest) option is to talk to the mobile provider and get business class service. That will most likely allow you to do what you need to do without constantly running through hoops.

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