Using both TCP and UDP protocols seem not to work on Ethernet Shield w5100

Hello,

I’m having a problem using both TCP and UDP in the same sketch. What appears to happen is that if the same socket is reused for UDP after it was in use for TCP, UPD fails to receive data. I was able to reproduce this with the WebServer example. I’ve added to it a DNS query once in every 10 seconds to query yahoo.com IP address. The DSN queries succeed if I’m not creating any client traffic from the browser. After I query the server over HTTP over TCP, the DSN queries start to fail. DNS queries are implemented in UDP. This is the code that I’m using:

​/*
  Web Server


 A simple web server that shows the value of the analog input pins.
 using an Arduino Wiznet Ethernet shield.


 Circuit:
 * Ethernet shield attached to pins 10, 11, 12, 13
 * Analog inputs attached to pins A0 through A5 (optional)


 created 18 Dec 2009
 by David A. Mellis
 modified 9 Apr 2012
 by Tom Igoe
 modified 02 Sept 2015
 by Arturo Guadalupi
 
 */


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


// Enter a MAC address and IP address for your controller below.
// The IP address will be dependent on your local network:
byte mac[] = {
  0xDE, 0xAD, 0xBE, 0xEF, 0xFE, 0xED
};
IPAddress ip(192, 168, 1, 177);


// Initialize the Ethernet server library
// with the IP address and port you want to use
// (port 80 is default for HTTP):
EthernetServer server(80);


unsigned long t0;


void setup() {
  // You can use Ethernet.init(pin) to configure the CS pin
  //Ethernet.init(10);  // Most Arduino shields
  //Ethernet.init(5);   // MKR ETH shield
  //Ethernet.init(0);   // Teensy 2.0
  //Ethernet.init(20);  // Teensy++ 2.0
  //Ethernet.init(15);  // ESP8266 with Adafruit Featherwing Ethernet
  //Ethernet.init(33);  // ESP32 with Adafruit Featherwing Ethernet


  // Open serial communications and wait for port to open:
  Serial.begin(9600);
  while (!Serial) {
    ; // wait for serial port to connect. Needed for native USB port only
  }

  Serial.println("Ethernet WebServer Example");


  // start the Ethernet connection and the server:
  Ethernet.begin(mac, ip);

  // Check for Ethernet hardware present
  if (Ethernet.hardwareStatus() == EthernetNoHardware) {
    Serial.println("Ethernet shield was not found.  Sorry, can't run without hardware. :(");
    while (true) {
      delay(1); // do nothing, no point running without Ethernet hardware
    }
  }
  if (Ethernet.linkStatus() == LinkOFF) {
    Serial.println("Ethernet cable is not connected.");
  }


  // start the server
  server.begin();
  Serial.print("server is at ");
  Serial.println(Ethernet.localIP());


  t0 = millis();
}




void loop() {
  // listen for incoming clients
  EthernetClient client = server.available();
  if (client) {
    Serial.println("new client");
    // an http request ends with a blank line
    boolean currentLineIsBlank = true;
    while (client.connected()) {
      if (client.available()) {
        char c = client.read();
        // if you've gotten to the end of the line (received a newline
        // character) and the line is blank, the http request has ended,
        // so you can send a reply
        if (c == '\n' && currentLineIsBlank) {
          // send a standard http response header
          client.println("HTTP/1.1 200 OK");
          client.println("Content-Type: text/html");
          client.println("Connection: close");  // the connection will be closed after completion of the response
          client.println("Refresh: 5");  // refresh the page automatically every 5 sec
          client.println();
          client.println("<!DOCTYPE HTML>");
          client.println("<html>");
          // output the value of each analog input pin
          for (int analogChannel = 0; analogChannel < 6; analogChannel++) {
            int sensorReading = analogRead(analogChannel);
            client.print("analog input ");
            client.print(analogChannel);
            client.print(" is ");
            client.print(sensorReading);
            client.println("
");
          }
          client.println("</html>");
          break;
        }
        if (c == '\n') {
          // you're starting a new line
          currentLineIsBlank = true;
        } else if (c != '\r') {
          // you've gotten a character on the current line
          currentLineIsBlank = false;
        }
      }
    }
    // give the web browser time to receive the data
    delay(1);
    // close the connection:
    client.stop();
    Serial.println("client disconnected");
  }
  if (millis() - t0 > 10000)
  {
    DNSClient dns;
    dns.begin(IPAddress(8,8,8,8));
    IPAddress yahoo;
    if (dns.getHostByName("yahoo.com", yahoo) == 1)
    {
      Serial.print("Yahoo: ");
      Serial.print(yahoo[0]);
      Serial.print(".");
      Serial.print(yahoo[1]);
      Serial.print(".");
      Serial.print(yahoo[2]);
      Serial.print(".");
      Serial.println(yahoo[3]);
    }
    else
    {
      Serial.println("Failed to query yahoo.com IP address");
    }
    t0 = millis();
  }
}

Is this a known issue? Can someone please help in identifying the problem in my code, or if there is a workaround for this issue? Can it be a hardware issue? I’m using SunFounder boards, not the original Arduino boards.

Thanks a lot,
Boaz,

Well, as I suspected, this appears to be a problem with w5100. After getting w5500 this problem disappeared. Same code works on w5500 and not on w5100.