Teensy 4.1 Ethernet Trouble Shooting


Well-known member
Hi All,

I'm having trouble getting a successful ping from my teensy 4.1 project using Ethernet. All I really need at this stage is to get a ping through to confirm the hardware is working.

For code, I've used the example chat server, just changing #20 to #include <NativeEthernet.h>

For the hardware

What I'm getting is a successful compile/program, Serial reports the Ip address, green light on the ethernet is lit/blinks, but I can't get a ping. I can ping another device using the same cable and port.

Any thoughts on what I'm doing wrong?

My five cents:
a) assuming you use DHCP in MCU FW, and you get an IP address - this sounds to me as: ETH is working, it can talk to DHCP server (and get IP address assigned).
b) but if you use a STATIC IP address in MCU, and Serial prints IP address - it does not mean anything (at least not for sure if ETH is working).
Is the IP address (for STATIC) the same as you computer is on the network?
If you are on different networks - a ping cannot work (without a gateway to bridge networks)
If you use DHCP (and you get IP address assigned as in your network) - you should be fine even without ping working:
Using DHCP and getting a "reasonable" IP address - ETH works, for sure.
c) other thought:
ping is a "specific" protocol, not sure if using <NativeEthernet.h> would enable and handle this protocol needed for ping.
ping is ICMP protocol, potentially not enabled neither handled by <NativeEthernet.h> (or without ETH handling code).

I use QNEthernet, AysncWebServer, here the ping works fine.
Assuming, potentially "just" using NativeEthernet, there is not any ICMP protocol handler running (and therefore ping does not work).

Even ping does not work - the ETH connection you want to handle might work, ETH is potentially still able to receive and send (esp. if DHCP works).
Just think about that ping is a specific protocol and when not handled - no ping, but other stuff might be fine.
Note: AsyncWebServer runs cooperatively and has similar behaviour and performance as polling/single-threading.

Deeper: it runs whenever QNEthernet’s `Ethernet.loop()` is run, and that happens internally in a few places when making API calls, in yield() calls, and after every iteration of the main program’s loop().
Thanks all.
I swapped to QNEthernet. The link was up immediately but the IP took a few minutes to get assigned.
Are you saying it took a few minutes to get an IP address from DHCP? If so, would you mind pasting a small example that demonstrates what you’re doing? DHCP doesn’t normally take that long. (Slow DHCP server, maybe?)
This is the code. It's basically just the setup code from the raw frame monitor. I confess once I'd got my ping that was enough to validate the hardware, so I've already passed the hardware on.
#include <QNEthernet.h>

using namespace qindesign::network;

// Main program setup.
void setup() {

  // Print the MAC address
  uint8_t mac[6];
  Ethernet.macAddress(mac);  // This is informative; it retrieves, not sets
  Serial.printf("MAC = %02x:%02x:%02x:%02x:%02x:%02x\r\n",
         mac[0], mac[1], mac[2], mac[3], mac[4], mac[5]);

  // Add listeners before starting Ethernet

  Ethernet.onLinkState([](bool state) {
    Serial.printf("[Ethernet] Link %s\r\n", state ? "ON" : "OFF");

  Ethernet.onAddressChanged([]() {
    IPAddress ip = Ethernet.localIP();
    bool hasIP = (ip != INADDR_NONE);
    if (hasIP) {
      IPAddress subnet = Ethernet.subnetMask();
      IPAddress broadcast = Ethernet.broadcastIP();
      IPAddress gw = Ethernet.gatewayIP();
      IPAddress dns = Ethernet.dnsServerIP();

      Serial.printf("[Ethernet] Address changed:\r\n"
             "    Local IP     = %u.%u.%u.%u\r\n"
             "    Subnet       = %u.%u.%u.%u\r\n"
             "    Broadcast IP = %u.%u.%u.%u\r\n"
             "    Gateway      = %u.%u.%u.%u\r\n"
             "    DNS          = %u.%u.%u.%u\r\n",
             ip[0], ip[1], ip[2], ip[3],
             subnet[0], subnet[1], subnet[2], subnet[3],
             broadcast[0], broadcast[1], broadcast[2], broadcast[3],
             gw[0], gw[1], gw[2], gw[3],
             dns[0], dns[1], dns[2], dns[3]);
    } else {
      Serial.printf("[Ethernet] Address changed: No IP address\r\n");

  // Initialize Ethernet, in this case with DHCP
  Serial.printf("Starting Ethernet with DHCP...\r\n");
  if (!Ethernet.begin()) {
    Serial.printf("Failed to start Ethernet\r\n");

// the loop routine runs over and over again forever:
void loop() {
  digitalWrite(led, HIGH);   // turn the LED on (HIGH is the voltage level)
  delay(1000);               // wait for a second
  digitalWrite(led, LOW);    // turn the LED off by making the voltage LOW
  delay(1000);               // wait for a second
Hmm. The code looks fine. Either the DHCP server is slow to respond or the network has high packet loss or something.
Interestingly that appears to happen with my system (Windows 11) when I run that code:

10:46:37.938 -> Starting...
10:46:37.938 -> MAC = 04:e9:e5:0f:69:fc
10:46:37.938 -> Starting Ethernet with DHCP...
10:46:37.938 -> [Ethernet] Link ON
10:50:35.432 -> [Ethernet] Address changed:
10:50:35.432 -> Local IP =
10:50:35.432 -> Subnet =
10:50:35.432 -> Broadcast IP =
10:50:35.432 -> Gateway =
10:50:35.432 -> DNS =

It takes 4 minutes to respond or am I reading that wrong....
That’s a self-assigned IP. What you’re seeing is a timeout; the system gives itself an IP after trying to contact a DHCP server for a while. Either your DHCP server isn’t responding or the Teensy isn’t plugged into a network that has a DHCP server. A DHCP-assigned address often takes about 5-10 seconds to arrive.

I think this also explains @Edward’s minutes-long delay. It’s a timeout; there’s no DHCP response.
Last edited: