I'm trying to connect my Arduino to the internet, but my Ethernet connection config code fails when I try to verify it, and I'm not sure why.

I'm using an Ethernet shield and have installed the Ethernet library v.2.0.0.

This is the running code:

WANStatus initialiseWAN() {
  // Enter a MAC address for your controller below.
  // Newer Ethernet shields have a MAC address printed on a sticker on the shield
  byte mac[] = { 0xDE, 0xAD, 0xBE, 0xEF, 0xFE, 0xED };
  WANStatus res;

  Serial.println("[INFO]: Initialising WAN");
  // Try to initialise Ethernet connecion

  if (Ethernet.begin(mac) == 0) {
    res.error = true;
    res.retry = true;
    if (Ethernet.hardwareStatus() == EthernetNoHardware) {
      res.message = "Ethernet shield was not found";
      Serial.print("[ERROR]: "); Serial.println(res.message);    
      return res;

    // If all component are present try assigning a static IP address
    IPAddress ip(192, 168, 0, 177);
    IPAddress myDns(192, 168, 0, 1);
    Ethernet.begin(mac, ip, myDns)
    Serial.print("[INFO]: Assigned static IP: "); Serial.println(Ethernet.localIP());
    if (Ethernet.linkStatus() == LinkOFF) {
      res.message = "Ethernet cable is not connected";
      Serial.print("[ERROR]: "); Serial.println(res.message);
      return res;
    if (Ethernet.linkStatus() == Unknown) {
      res.message = "Ethernet link status is 'Unknown' check the cable";
      Serial.print("[ERROR]: "); Serial.println(res.message);
      return res;

    // Static IP assigned
    res.error = false;
    res.retry = false;
    res.message = "Static IP Address";
    return res;
  } else {
    // Received IP address from DHCP
    Serial.print("[INFO]: Received DHCP IP: "); Serial.println(Ethernet.localIP());
    res.error = false;
    res.retry = false;
    res.message = "DHCP IP Address";    
    return res;

  // ToDo: check WiFi modules here


And the error message:

enter image description here

[Starting] Verifying sketch 'controller\controller.ino'
[Warning] Output path is not specified. Unable to reuse previously compiled files. Build will be slower. See README.
Loading configuration...
Initialising packages...
Preparing boards...
In file included from C:\Program Files (x86)\Arduino\libraries\Ethernet\src\Dns.cpp:8:0:
C:\Program Files (x86)\Arduino\libraries\Ethernet\src\Dns.cpp: In member function 'uint16_t DNSClient::BuildRequest(const char*)':
C:\Program Files (x86)\Arduino\libraries\Ethernet\src\utility/w5100.h:457:25: warning: result of '(256 << 8)' requires 18 bits to represent, but 'int' only has 16 bits [-Wshift-overflow=]
#define htons(x) ( (((x)<<8)&0xFF00) | (((x)>>8)&0xFF) )
C:\Program Files (x86)\Arduino\libraries\Ethernet\src\Dns.cpp:164:18: note: in expansion of macro 'htons'
Sketch uses 22574 bytes (69%) of program storage space. Maximum is 32256 bytes.
Global variables use 1467 bytes (71%) of dynamic memory, leaving 581 bytes for local variables. Maximum is 2048 bytes.
IntelliSense configuration already up to date. To manually rebuild your IntelliSense configuration run "Ctrl+Alt+I"
[Done] Verifying sketch 'controller\controller.ino'

1 Answer 1


Everything is alright. There is no compiler error and your sketch is ready to upload.

The compiler warning "result of '(256 << 8)' requires 18 bits to represent, but 'int' only has 16 bits" from the Ethernet library source code is nothing you have to worry about.

  • the warning is fixed in Ethernet 2.0.1 released Jul 6, 2022
    – Juraj
    Feb 10, 2023 at 6:43

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