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Thread: Native Ethernet on Teensy 4.1

  1. #1
    Junior Member
    Join Date
    Jun 2021

    Native Ethernet on Teensy 4.1


    I'm trying to get started with the native Ethernet on Teensy 4.1 but I can get the UDPSendReceiveString example to work. It works fine on an Arduino Uno with Ethernet shield so on the PC side the script is working fine.
    I don't know much about network communication, are there any steps that I'm missing or settings that I can try?


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    #include <NativeEthernet.h>
    #include <NativeEthernetUdp.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, 0xAD
    IPAddress ip(192, 168, 0, 20);
    unsigned int localPort = 8888;      // local port to listen on
    // buffers for receiving and sending data
    char packetBuffer[UDP_TX_PACKET_MAX_SIZE];  // buffer to hold incoming packet,
    char ReplyBuffer[] = "acknowledged";        // a string to send back
    // An EthernetUDP instance to let us send and receive packets over UDP
    EthernetUDP Udp;
    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
      // start the Ethernet
      Ethernet.begin(mac, ip);
      // Open serial communications and wait for port to open:
      while (!Serial) {
        ; // wait for serial port to connect. Needed for native USB port only
      // 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 UDP
    void loop() {
      // if there's data available, read a packet
      int packetSize = Udp.parsePacket();
      if (packetSize) {
        Serial.print("Received packet of size ");
        Serial.print("From ");
        IPAddress remote = Udp.remoteIP();
        for (int i=0; i < 4; i++) {
          Serial.print(remote[i], DEC);
          if (i < 3) {
        Serial.print(", port ");
        // read the packet into packetBufffer, UDP_TX_PACKET_MAX_SIZE);
        // send a reply to the IP address and port that sent us the packet we received
        Udp.beginPacket(Udp.remoteIP(), Udp.remotePort());

  2. #2
    Junior Member
    Join Date
    Jun 2021
    Correction: can't get it to work

  3. #3
    Senior Member+ manitou's Avatar
    Join Date
    Jan 2013
    Your sketch works for me. What do you observe? Packet is never received ? or reply is not seen by sender? can you ping the Teensy 4.1?
    Can you run wireshark/tcpdump and and observe the packets ?

    do any of the NativeEthernet examples work for you?

    Probably should zero packetBuffer before -- cosmetic

  4. #4
    Senior Member BriComp's Avatar
    Join Date
    Apr 2014
    Cheltenham, UK
    What version of Arduino and Teensyduino are you using?
    Latest Teensduino in beta includes corrections for NativeEthernet.

  5. #5
    Junior Member
    Join Date
    Jun 2021
    Thanks, I installed the newest version of Teensyduino and now it works!

    I was indeed not receiving any packets. Thanks for referring me to Wireshark, what an awesome tool! I expect it will make my life a lot easier going forward.

    Indeed it would be cleaner to clear packetBuffer before writing to it, shall do!

    Many thanks!!

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