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  1. Qt
  2. QTBUG-27641

Multicast joining fails on multiple interfaces

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Details

    • Bug
    • Resolution: Done
    • P3: Somewhat important
    • 5.9.0 Beta 2
    • 4.8.x, 5.7.0
    • Network: Sockets
    • None
    • Windows, Linux
    • 4c367833b4c1776f01eff3d51472a9889c85e1c5

    Description

      When trying to use QUdpSocket::joinMulticastGroup with multiple interfaces it often fails under certain conditions.

      After looking into the source code of qnativesocketengine_*.cpp I found the following code that is actually incorrect:

                  QList<QNetworkAddressEntry> addressEntries = iface.addressEntries();
            if (!addressEntries.isEmpty()) {
                QHostAddress firstIP = addressEntries.first().ip();
                mreq4.imr_interface.s_addr = htonl(firstIP.toIPv4Address());
            } else {
                d->setError(QAbstractSocket::NetworkError,
                            QNativeSocketEnginePrivate::NetworkUnreachableErrorString);
                return false;
            }

      This code takes the first address from the list and assumes it is an IPv4 address (which might not be true).
      The proper approach would be to iterate through the list and check for IPv4 protocol:

      	QList<QNetworkAddressEntry> addressEntries = iface.addressEntries();
		for (int i = 0; i < addressEntries.length(); i++) {
			if (addressEntries[i].ip().protocol() == QAbstractSocket::IPv4Protocol) {
				...
				break;

      Attachments

        Issue Links

          is duplicated by

          Bug - A problem which impairs or prevents the functions of the product. QTBUG-61888 UDP Multicast on Specific Network Interface

          • P2: Important - Urgent, should be fixed, but will not stop the release.
          • Closed
          replaces

          Bug - A problem which impairs or prevents the functions of the product. QTBUG-30949 QUdpSocket join to group error

          • P2: Important - Urgent, should be fixed, but will not stop the release.
          • Closed

          Bug - A problem which impairs or prevents the functions of the product. QTBUG-53127 Windows: Trying to join to a multicast group as a receiver with specific interface always uses default interface

          • P2: Important - Urgent, should be fixed, but will not stop the release.
          • Closed
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          Activity

            People

              Eddy Edward Welbourne
              dremon Dmitry Pankratov
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              5 Vote for this issue
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              11 Start watching this issue

              Dates

                Created:
                Updated:
                Resolved:

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