Multicast with QUdpSocket and QHostAddress::Any does not work

kzawada

For some reason I just recently ran into an issue with this.

I configure the bind the following way:
m_udpSocket.bind(QHostAddress::Any, 2222);

then eventually when I want to respond to a message I call:
qint64 dataWritten = poUdpSocketIo->writeDatagram(Data, qhaIPv4Addr, 2222);

a qDebug() message is printed that showns:
SUCCESS on writeDatagram() | dataWritten: 128 | Data.size(): 128

However, when I use Wireshark I can see that this message never goes out on the wire.

If I change the bind call to the following:
m_udpSocket.bind(QHostAddress("192.168.100.3"), 2222);

This multicast works perfectly fine and I can see packets being sent to multicast address 239.192.1.65.

I have another computer setup with Windows 7 just like this failing one and I can see that even with QHostAddress::Any this still works.

What could be wrong? Why is the multicast not working when the bind() call is passed QHostAddress::Any when it used to work and it works this way on another computer?

SGaist

Hi,

On what OS/Qt combo do you have the failure ?

kzawada

@SGaist I am running on Windows 7 Professional Service Pack 1 (64-bit Operating System). Also tried with both Qt 5.4.1 32-bit and Qt 5.3.1 32-bit.

SGaist

And it's falling only on that one computer ?

kzawada

@SGaist Yes, it used to work on that computer previously.

The only difference I have noticed so far it he following output using command prompt:

FAILING COMPUTER

C:\>netsh interface ip show join "Local Area Connection"

Interface 11: Local Area Connection


Multicast Address : 224.0.0.1
Scope             : 0
References        : 0
Last Reporter?    : Yes

Multicast Address : 224.0.0.252
Scope             : 0
References        : 1
Last Reporter?    : Yes

Multicast Address : 239.255.255.250
Scope             : 0
References        : 2
Last Reporter?    : Yes


C:\>

WORKING COMPUTER

C:\>netsh interface ip show join "Local Area Connection"

Interface 13: Local Area Connection


Multicast Address : 224.0.0.1
Scope             : 0
References        : 0
Last Reporter?    : Yes


C:\>

I'm not sure if it is because the failing computer is showing two more Multicast Addressed. In which case I don't know how to remove the other two addresses.

SGaist

Got several network cards ?

kzawada

@SGaist No just one.

SGaist

Did you check with the latest Qt 5.5 if you still experience this behavior ?