Make setSocketOption + QAbstractSocket::MulticastTtlOption work!

ruehlchr

Hi Guys,

I have a small project working and debug the ttl of a multicast udp datagram using tcpdump.
Its turns out that the
setSocketOption(QAbstractSocket::MulticastTtlOption,QVariant(4)) has no effect
tcpdump shows ttl=1

I'd followed the sample code:
http://qt-project.org/doc/qt-4.8/network-multicastsender-sender-cpp.html

Here my finding:
not work:
udpSocket = new QUdpSocket(this);
udpSocket->setSocketOption(QAbstractSocket::MulticastTtlOption, QVariant(4));

11:38:41.994031 IP (tos 0x0, ttl 1, id 6402, offset 0, flags [DF], proto UDP (17), length 37)
10.128.2.32.59388 > 239.255.43.21.45454: [udp sum ok] UDP, length 9

work:
DCMCASTPORT=45454
udpSocket = new QUdpSocket(this);
udpSocket->bind(DCMCASTPORT);
udpSocket->setSocketOption(QAbstractSocket::MulticastTtlOption, QVariant(4));

12:15:43.285005 IP (tos 0x0, ttl 4, id 57649, offset 0, flags [DF], proto UDP (17), length 37)
10.128.2.32.57081 > 239.255.43.21.45454: [udp sum ok] UDP, length 9

May this find the way into the demo code.

Happy Hacking!
Chris

SGaist

Hi,

From the forum it's pretty unlikely that it'l get to the example code however if you would like to update the example, you can provide a patch and contribute it to Qt