Ethernet can't connect at first time and problem with a domain without public IP

Projects Networking, Protocols, and Devices
1

Hi all. Ethernet shield can't connect at first time. At second try everything works good. At first time I must wait for a while, next try is really fast (normal). What causes this problem?

I'm using this code:

//zoomkat 9-22-12
//simple client test
//for use with IDE 1.0.1
//with DNS, DHCP, and Host
//open serial monitor and send an e to test
//for use with W5100 based ethernet shields

#include <SPI.h>
#include <Ethernet.h>

byte mac[] = { 0xDE, 0xAD, 0xBE, 0xEF, 0xFE, 0xED }; //physical mac address

char serverName[] = "web.comporium.net"; // zoomkat's test web page server
EthernetClient client;

//////////////////////

void setup(){

  if (Ethernet.begin(mac) == 0) {
    Serial.println("Failed to configure Ethernet using DHCP");
    // no point in carrying on, so do nothing forevermore:
    while(true);
  }

  Serial.begin(9600); 
  Serial.println("Better client test 9/22/12"); // so I can keep track of what is loaded
  Serial.println("Send an e in serial monitor to test"); // what to do to test
}

void loop(){
  // check for serial input
  if (Serial.available() > 0) //if something in serial buffer
  {
    byte inChar; // sets inChar as a byte
    inChar = Serial.read(); //gets byte from buffer
    if(inChar == 'e') // checks to see byte is an e
    {
      sendGET(); // call sendGET function below when byte is an e
    }
  }  
} 

//////////////////////////

void sendGET() //client function to send/receive GET request data.
{
  if (client.connect(serverName, 80)) {  //starts client connection, checks for connection
    Serial.println("connected");
    client.println("GET /~shb/arduino.txt HTTP/1.0"); //download text
    client.println("Host: web.comporium.net");
    client.println(); //end of get request
  } 
  else {
    Serial.println("connection failed"); //error message if no client connect
    Serial.println();
  }

  while(client.connected() && !client.available()) delay(1); //waits for data
  while (client.connected() || client.available()) { //connected or data available
    char c = client.read(); //gets byte from ethernet buffer
    Serial.print(c); //prints byte to serial monitor 
  }

  Serial.println();
  Serial.println("disconnecting.");
  Serial.println("==================");
  Serial.println();
  client.stop(); //stop client

}

And the result is:

Better client test 9/22/12
Send an e in serial monitor to test
connection failed


disconnecting.
==================

[b]//second send an "e" and:[/b]

connected
HTTP/1.1 200 OK
Date: Mon, 02 Sep 2013 21:10:27 GMT
Server: Apache
Last-Modified: Sat, 13 Nov 2010 16:31:40 GMT
Accept-Ranges: bytes
Content-Length: 51
Connection: close
Content-Type: text/plain; charset=UTF-8

Woohoo! Your arduino ethernet client works!
zoomkat
disconnecting.
==================

Why that? In local network it works fine from the beginning. And why I can't connect with a domain without public IP? It just connects with IP, which is shared. How improve that? Please help.

2

It is usually dns resolution that causes the delay. That would be up to the local ISP and dns servers. The initial resolution request may time out before the Arduino gets a response, so without the destination ip, the connection will fail.

The alternative is resolve the domain beforehand, and use that ip address. Like zoomkat's code above, use this. I used nslookup to resolve that domain name.

//Replace this
//char serverName[] = "web.comporium.net"; // zoomkat's test web page server
// with this
IPAddress serverName(208,104,2,86);

Does that do any better first time through?

3

Unfortunately there is no difference. Still I must wait ~25 seconds and I see "connection failed" :astonished: Second try works great. Any ideas?

4

I can't see a reason in zoomkat's code. It should connect fine first time through. The only thing I could think of is a fussy router, but that is rare. The code does not make any unusual type requests that would cause a router to hesitate or fail.

Have you tried waiting several seconds before sending the request?

5

Still no difference, I've tp-link tl-wr740n router, with a new firmware. I even changed ethernet cable. A few hours of trying and searching web - without results.

And off course thanks for your feedback :slight_smile: