Arduino DDNS (Dynamic DNS)

By on April 8, 2011
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This device captures the IP address of your network and it publish on site All without PC. It allow a remote access to your LAN even if the IP address of the connections changes.
For logistics reasons the provider can not assign a IP fixed for all users, so many users, especially private, work with a dynamic IP or public IP: in practice when they connect modem or router, to their connection is assigned an IP address that, when the connection will’be closed, can be used by other users. This makes impossible to contact a remote computer or device connected to a LAN Internet.

If you want to access to a device connected to your home LAN (so not with static IP) you must use a service like DynDNS, because every time you connect your ISP dynamically assigns a new IP address.

If you don’t want to use the software provided by DynDNS, and then leave the PC switched on continuously, the solution is this project.
Our device queries the site to know the IP currently used for the connection, and then publish your free account to instead of the computer acquired the new IP. Such a device therefore allows to locate a LAN connected to the Internet via a router or modem network.

Our device is essentially a publisher of IP address. Everything is made ​​from a circuit that incorporates an Ethernet interface WIZnet WIZ811MJ, managed by an Atmega328 microcontroller programmed with the Arduino bootloader, so it all works like an Arduino and you can use the Arduino IDE. The Atmega I/O PB2, PB3, PB4 and PB5 are dedicated to dialogue with the Ethernet module and provide a full four-wire SPI bus. The microcontroller is programmed using the special interface TTL / USB from SparkFun.
The main program sends the request to the IP address site. Now prepare the process of submitting to the site, which provides for the opening of a session onthe web page on, where will send data strings containing user name and password, thena string containing the Current IP connection. Cyclically
the microcontroller check the IP to see if the address is changed, then, if it’s true, sends the new IP to

We use a dedicated circuit but the project can be replicated using an Arduino UNO and a Ethernet Shield.

Sketch Code for Arduino DDNS (Dynamic DNS)

/* DynDNS

 created 2011
 by Boris Landoni

 This example code is in the public domain.


#include <Ethernet.h>
//#include <EthernetDNS.h>
#include <WString.h>
#include <EEPROM.h>

#define UPDATE_INTERVAL            30000    // if the connection is good wait 30 seconds before updating again - should not be less than 5

int ledR =  8;
int ledG =  9;

unsigned long pubblica=0;

byte mac[] = { 0x54,0x55,0x58,0x10,0x00,0x24 };
byte ip[] = { 192, 168, 0, 98 };

byte domainaddrip[]= { 208, 78, 70, 70 }; //
byte ipAddr[4];

byte domaindydns[]= { 204, 13, 248, 112 }; //
char hostname[ ]   = "";
char userpwdb64[ ] = "xxxxxxxxxxxxxxxxxx";  //    use->   username:password

String ipadsl     = String(20);
String ipadslold  = String(20);
String inString   = String(51);

//Client client(server, 80);
const char* ip_to_str(const uint8_t*);
//void nameFound(const char* name, const byte ipAddr[4]);

Client client(domainaddrip, 80);
Client clientdyn(domaindydns, 80);

void setup()
  pinMode(ledR, OUTPUT); 
  pinMode(ledG, OUTPUT); 
  Ethernet.begin(mac, ip);




void loop()

  if (millis() < pubblica) pubblica = millis();

      if ((millis() - pubblica) > UPDATE_INTERVAL){
          //Serial.print("Passati "); 
          //Serial.println(" ms"); 
          Serial.print("tempo trascorso dall'accensione ");          
          pubblica = millis();  



void acquisisciip()

  int timeout=0; 
  int skip=0;
  digitalWrite(ledG, HIGH);

  Serial.print("connecting to ");
  //Serial.print(" = ip ");

  if (client.connect()) {

    client.println("GET / HTTP/1.0");
    //client.println("GET / HTTP/1.0");
    client.print("HOST: ");
  } else {
    Serial.println("connection failed");

  while (!client.available() && timeout<50) 
    Serial.print("Time out ");

  while (client.available()) 
      //if (client.available()) 
        char c =;
        if (skip>220)
          if ((inString.length())<50) inString.append(c);      



      if ((inString.length())>5)   
          //Serial.print("inString: ");
          if (inString.contains("Address"))
              int from=(inString.indexOf("Address")+9);
              int lunghe=inString.length();
              int to=(lunghe-16);
              /*Serial.print("Lunghezza instring    = ");
              Serial.print("Posizione address + 9 = ");
              Serial.print("Posizione fine   - 16 = ");
              //Serial.print("Lunghezza ipadsl      = ");
              Serial.print("IP rilevato dal sito: >");


   if (!client.connected()) 

        delay (1000);

        Serial.print("lunghezza IP ");

        if ((strlen(ipadsl))!=0)
              Serial.print("IP nuovo  : >");

              for (int i=0; i<(ipadsl.length()); i++) {    //salva in memoria l'indirizzo acquisito
                ipadslold[i] =;
                //Serial.print("carattere  : >");

              Serial.print("IP vecchio: >");

              if (strcmp(ipadsl,ipadslold))
                Serial.println("IP diverso PUBBLICO");
                  digitalWrite(ledR, HIGH);
                  digitalWrite(ledR, LOW);
                Serial.println("IP uguale");    

                digitalWrite(ledG, LOW);

              //Serial.print("IP vecchio azzerato: >");
              for (int i=0; i<(ipadsl.length()); i++) {    //salva in memoria l'indirizzo acquisito
                EEPROM.write(i, ipadsl[i]); 




void pubblicaip()
  int timeout=0;
  Serial.print("connecting to ");

  Serial.print("IP da pubblicare ");

if (clientdyn.connect()) {
    clientdyn.print("GET /nic/update?hostname=");
    clientdyn.println(" HTTP/1.0 ");
    //clientdyn.println("Host: ");

    clientdyn.print("Host: ");

    clientdyn.print("Authorization: Basic ");

    clientdyn.println("User-Agent: futura - arduinodydns - 1.1");
  } else {
    Serial.println("connection failed");

 //   delay(3000);

  while (!clientdyn.available() && timeout<50) 
    Serial.print("Time out ");

  while (clientdyn.available()) 
      if (clientdyn.available()) 
        char c =;

  if (!clientdyn.connected()) 


// This is just a little utility function to format an IP address as a string.
const char* ip_to_str(const uint8_t* ipAddr)
  static char buf[16];
  sprintf(buf, "%d.%d.%d.%d\0", ipAddr[0], ipAddr[1], ipAddr[2], ipAddr[3]);
  return buf;


Download ZIP File

Download the DDNS sketch for Arduino


<span style="font-family: Consolas, Monaco, 'Courier New', Courier, monospace; font-size: 12px; line-height: 18px; white-space: pre;">R1, R2: 470 ohm</span>
<span style="font-family: Consolas, Monaco, 'Courier New', Courier, monospace; font-size: 12px; line-height: 18px; white-space: pre;">R3: 10 kohm</span>
C1: 100 nF
C2: 470 μF 25 VL
C3: 100 nF
C4: 470 μF 16 VL
C5: 15 pF
C6: 15 pF
C7: 100 nF
U2: ATMEGA328P (with Arduino bootloader)
U3: LD1086V33
P1: Microswitch
LD1: LED 3 mm yellow
LD2: LED 3 mm red
Q1: Quarzo 16 MHz
D1: 1N4007
power jack
Dip socket 14+14
Break away headers  male 6 via
Break away headers  female 2x10 via (2 pz)

About Boris Landoni

Boris Landoni is the technical manager of Skilled in the GSM field, embraces the Open Source philosophy and its projects are available to the community.
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  • Dave

    Great project! What are your values for C5, C6, & C7? I don’t see them listed in the BOM. Same with Q1 though I imagine that is the standard 16MHz crystal oscillator.


  • Ops… :-)
    I add the components.

  • Xiszone

    It is a very nice project and exactly what i need.
    It is possible to buy the assembled bord from you?

  • Hi, we can sell only
    U1: WIZNET
    U2: ATMEGA328P (with Arduino bootloader)
    We haven’t the PCB.

  • dmsherazi

    HI , Nice work , I wanted to implement the dyndns in my project, but i am not fimilair with aurduinos, can u please let me know how would i update my ip address on dyndns using AT commands . I know i have to send

    but how to do that in AT commands i am usnig the same sim900

  • I suggest you to study this firmware
    You have to connect to the site adding the parameters.

  • dmsherazi

    HI , thanks for ur prompt reply …

    I checked dyndns support and also the firmware and then connected to the

    and sent this data

    GET /nic/update? HTTP/1.0
    Authorization: Basic a2lxxxxxxxxxxxxxx3M=
    User-Agent: kindows- 12hh- 1.1

    but i get badagent in responce when i connect to port 8245 , if i conncet to port 80 i get no reponse!!

  • Hi, Try to post your problem on facebook

  • @ BORIS

    hi its dm sherazi here, actually i got the problem solved the problem was with the hyperterminal , i used docklight and it worked well, and then when i programmed my mcu its still working great .

  • hi dmsherazi, this is a good news. ;-)

  • Snooper1

    I like your dyn DDNS project. I’m having issues trying to use IDE 1.01

    I have a Arduino UNO V3

    And a Arduino Mega V3

    Both use the Arduino Ethernet shield

    What Arduino build did you use?

    Can you help to update it to the latest Arduino IDE?

  • clayzz jr

    Hello.. i have a problem..
    When the first run of program.. it works fine and update my ip to dyn.
    When i connect to second time after 30 sec .. it just connect and disconnecting.. and i must reset arduino to update again.. any help ?

  • Anil

    Doesn’t the router have to do the DDNS? Or is the Arduino here acting as the router? If my router has DDNS, I will simply use that and NAT the Arduino’s IP.