It should be pretty easy to plug this code into a project, instantiate a NetworkTest object and call ‘Start’ on it.  Please see the last section for further explanation of what’s happening.


// Declaration

#include <QDebug>
#include <QNetworkAccessManager>
#include <QNetworkConfigurationManager>
#include <QNetworkConfiguration>
#include <QNetworkReply>
#include <QNetworkRequest>

class NetworkTest : public QObject
{
  Q_OBJECT

public:
  void Start();

private:
  QNetworkConfigurationManager net_config_mgr_;
  QNetworkAccessManager net_access_mgr_;
  void HandleNetworkResponse(QNetworkReply *reply);

private Q_SLOTS:
  void Continue();
};


// Implementation

void NetworkTest::Start()
{
  qInfo() << "START NETWORK TEST, Qt Version:" << qVersion();
  connect(&net_access_mgr_, &QNetworkAccessManager::finished, this, &NetworkTest::HandleNetworkResponse);
  connect(&net_config_mgr_, &QNetworkConfigurationManager::updateCompleted, this, &NetworkTest::Continue);
  net_config_mgr_.updateConfigurations();
}

void NetworkTest::Continue()
{
  qInfo() << "CONTINUE NETWORK TEST";
  QList<QNetworkConfiguration> configs = net_config_mgr_.allConfigurations(QNetworkConfiguration::Discovered);
  QNetworkConfiguration testConfig;

  for (QListIterator<QNetworkConfiguration> itr(configs); itr.hasNext(); )
  {
    QNetworkConfiguration config = itr.next();

    qInfo() << "CONFIG:" << config.name() << "ID=" << config.identifier();

    // Select a configuration that does not have internet access.
    if (config.name().startsWith("utun0"))
    {
      testConfig = config;
    }
  }

  if (testConfig.isValid())
  {
    QNetworkRequest request(QUrl("http://www.suitabletech.com/wifi_verify.html"));

    qInfo() << "SEND REQUEST VIA CONFIG:" << testConfig.name() << "ID=" << testConfig.identifier();
    net_access_mgr_.setConfiguration(testConfig);
    net_access_mgr_.get(request);
  }
}

void NetworkTest::HandleNetworkResponse(QNetworkReply *reply)
{
  if (reply->error() == QNetworkReply::NoError)
  {
    QNetworkAccessManager *net_access_mgr = reply->manager();

    qInfo() << "GOT REPLY VIA CONFIG:" << net_access_mgr->configuration().name() << "ID=" << net_access_mgr->configuration().identifier() << "DATA=" << reply->readAll();
  }
  else
  {
    qInfo() << "NETWORK TEST ERROR: " << (int)reply->error();
  }
}


// Output

START NETWORK TEST, Qt Version: 5.8.0
CONTINUE NETWORK TEST
CONFIG: "en0" ID= "287176529"
CONFIG: "utun0" ID= "312537764"
CONFIG: "utun1" ID= "312537765"
SEND REQUEST VIA CONFIG: "utun0" ID= "312537764"
GOT REPLY VIA CONFIG: "utun0" ID= "312537764" DATA= "OK\n"


// Explanation

So as you can see, I tell the network access manager to use “utun0” and it apparently succeeds. The problem is that the “utun0” interface has no internet access and I can see in Wireshark that it’s actually using the one that does, “en0”.