I admit that this is a subject that is really really basic and no doubt explained at many places. Yet, I still see the question posed time after time at various fora and sadly the replies are often not on the ball. Things like “You need REST API”, “Just use Blynk”, “Just use IFTTT” or “Why would you want to do that”, surely will not help the struggling novice on their way.
So, rather than having to repeat my explanation again and again, it is better, I just write an article, explaining it…..for the novices amongst us.
Finding 2 IP addresses
OK, so you have an ESP8266 that reads a sensor and you want to be able to get the reading when you are away from home, using internet. It is quite simple, but you need to know 2 distinct IP addresses.
1- you need to know the IP address that connects your computer to the internet. You can easily find that on websites like “whatismyip.com“. It is also called ‘Public IP’ or ‘WAN IP’
2- you need to know the IP address that your ESP8266 has in your local network. You need to check the DHCP table in your router, but many ESP8266 programs actually print that number as well in the serial port. These numbers almost always looks like “192.168.x.yyy”. You can also use a phone app like ‘port authority’ to find the number for you.
So what happens when you are on your holiday address in Reykjavik or Kabul and you want to know what your sensor back home says? You open a browser, type in the IP address you found under “1”. well that connects you via the internet to your router back home. However, your router when it gets that call, doesn’t have a clue what to do with it, let alone that it knows it should forward that call to the ESP8266 that is connected to it, because you didn’t tell it what to do with it.
So when you get back home you have to instruct your router to forward the calls to your ESP8266 and that is done via “IP forwarding” or “Port forwarding”.
What makes that a bit complicated is that it is done differently in various routers, so you would have to check your specific router for it. Look for “IP forwarding” or “Port forwarding” and in some routers it is called ‘virtual server’.
When you found that you usually have to fill out 2 things. The port that is being forwarded and the IP address it has to be forwarded to. For the port you choose “80” and for the IP address to forward to, you use the local ip address, you found under point “2”.It is the address that started with “192.168.”
If it doesnt allow you to forward a specific port, but it does allow you to forward a service, choose ‘http’ for that service.
If you really cant find the port forwarding, but You happen to find something that is called “DMZ” choose that to forward to the ip address of your ESP8266 (the address starting with “192.168”) that is less elegant, but it will work.
Setting up a Webserver
So you are back on holiday and you want to check again. You fill out the internet IP number of your home system (the number you found under “1” and yes, this time the call comes in to your router and that one knows exactly what to do,so it forwards the call to your ESP8266. The ESP duly receives the call and……….has no idea what to do with it because chances are you didnt tell it what to so with it.
Your ESP8266 needs a program that presents the data in “Webpage”. That is not hard, there are plenty of programs who do that. These programs usually are called “Webservers”. Plenty of those available. (Look in your Arduino IDE examples or check e.g. randomnerdstutorial.)
It works!!!! for now: MAC and Address reservation
So, you now have programmed your ESP8266 with a webserver program that presents the sensor data on its own little webpage.
In order to test it when you are at home you open your browser and fill out the Local IP number (that you found under “2” starting with 192.168) and yes, you see the webpage. To make sure you also fill out the address you found under “1” (thus the address that your system has on the worldwide interweb) and great it all works. You go back on holiday and check from the other side of the world and great still works. Mission accomplished!!!
…..or is it. Suddenly it doesn’t work anymore. What on earth is wrong????? Well chances are that you have restarted your ESP8266 a few times and suddenly it has received a different IP address in your Local network. Say it once had 192.168.1.103, but now you find out it has 192.168.1.110. Your router however still sends the incoming call to the first IP number because that is what you told it to do. Now it is hardly feasible that you constantly check if the local IP is still the same and if it isnt that you keep changing your forward instructions.
Fortunately, most routers allow you to reserve a specific IP number in your network, for a specific device, and this is how you do it:
When you earlier found the IP number of your ESP8266 (the one starting with 192.168), you probably also found its MAC number. A MAC number (or addres rather) looks something like: “5D:CF:7F:AC:61:66”
Now you need to look in your router that is called “MAC binding” or “Address reservation”. The object here is that you give the MAC number, as well as the IP number (192.168.xx.yyy) that should always be reserved just for the device with that specific MAC stands for “media access control”.
Yes, works again
OK you got that done,so now whenever you go to the internet address of your system back home, the call comes into your router, the router knows what internal address to send it to, that address is always the same, and the device on that address knows what to do: it presents (“serves”) a webpage to the computer half across the world behind which you are sitting. That webpage can present data, but it may just as well receive commands from you, e.g. to turn a lamp on or off. Realuse though that anybody who knows your public IP address can also check that webpage. That might not be so bad if it just presents temperature, but it might give a problem if strangers can switch a lamp off and on in your home. So once you set it all up, you may consider making a password protected webpage.
Let me compare the situation with making a phonecall to a hotel: you need the hotel’s phonenumber (compare to the internet IP) and you need to know what room someone is in (the Local IP). The person in the room needs to know what to do with your questions (serving a webpage). That all works well as long as the person is in the same room (the address reservation: when Mr MAC comes to the hotel, he always gets room 192.168.1.103).
A final touch: DNS providers
So, everything works now………..but what if there is a rezoning and the hotel’s phonenumber changes???? Yes, you could look up the new number, but it is hardly practical.
But what does that mean in internet terms? Well, most of us get a so called ‘Dynamic IP address’ from our provider. Usually those addresses stay the same for a long time, but when you happen to restart your router you could get a different internet IP address. Sure you could check your internet address regularly, but that is only possible when you are at home. What to do when you are away from home????
The solution is a (free) DNS provider.
DNS providers provide you with an internet name, that you can use rather than an IP number. The essence though is that you get to put a tiny bit of software on your computer, that regularly checks your internet address and if that changes, it tells your DNS provider what the new number is. So you only have to provide a domain name to your browser and the DNS provider then knows the most up to date IP number to connect to.
A popular freeDNS provider for instance was “noip.com”, but there are more.