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I have been looking for an answer to this problem, but I cannot find what I am looking for. I think, perhaps, it is because I lack the knowledge to ask the question in meaningful way.

I have been learning a lot about remote access to devices at home. I know that ISP's change public IP addresses regularly (dynamic IP address). I know that to get around this, one could use a service like "no-ip", etc. Or one could get a static IP address.

What I do not understand is how some of the latest home automation devices are able to be controlled remotely without use of a static IP, or a service like "no-ip". For example, a wifi enabled thermostat, or lighting system.

If the device had a built in server, or client, then I assume that the device could connect to an outside server in a remote location. The user could then also log into that server and send commands to the device. What I don't understand is how commands sent to the device from a cell phone, for example, can reach the home device. Presumably the off site location of the server would have to know the public IP address where the devise is located, and then port-forwarding would have to be set up to allow access to the device.

What am I missing here? Is it possible to create a homemade wifi enabled thermostat, webcam, or other device without using port-forwarding, no-ip, or a static IP?

NorMi45
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Well, there are several ways to bypass the inbound connection constraint of NAT protocol. Such as:

  • A virtual adapter on the device configured to a VPN server that has an inbound port open ready to transfer data. Various open source solutions such as openVPN are considered as great examples for this service over IOT boards like Raspberry Pi, Beagle Bone, etc. These are used as gateways often. Further, they communicate with the microcontrollers over popular IOT protocols such as MQTT, COAP, etc.

  • Another solution is to create a port forwarding tunnel, since the router won't block the outbound connection. There are various tunneling services that are availble such as localtunnel, ngrok, etc. You could also use a cloud server that has a public IP such as AWS, DigitalOcean, etc. Again as above mentioned point, they can be implemented in the gateways.

Trishant Pahwa
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Some devices "phone home" to a server so that there are ports open between them and the servers, and the mobile apps just contact the servers. This is the same way your web browser can receive web pages from a web server. If you have a NAT router, the router must open a port from the inside device to the outside server. This is maintained in a NAT table with expiration timers for UDP and session monitoring for TCP.

Ron Maupin
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