On Tue, Oct 2, 2018 at 5:02 PM Murphy, Sean <smur...@walbro.com> wrote: > > > I have an app (Desktop) that I want it to know about other running instances > > on the local network. I figured UDP broadcast was a natural choice. I tried > > it, > > but I never saw anything but my own (local) packets. There's quite a few > > stackoverflow questions, but none used Qt. I'm wondering if it's a > > wifi/router > > thing? > > A couple of first questions: > - do you have any sort of firewalls running anywhere? > - have you tried the Qt Networks examples, and do those work? > http://doc.qt.io/qt-5/qtexamples.html#qt-network, maybe the Broadcast > Sender & Receiver examples > > Sean > Hi, 1. As Sean has mentioned, firewall settings that do not allow broadcasts could be the case.
2. Yet another case could be: QHostAddress::Broadcast. It's so-called All-Networks-Broadcast (255.255.255.255) and normally requires alleviated privileges to send to (UNIX root, suid) and could be guarded. There's another broadcast address - so-called LAN-broadcast which is less sensitive and more appropriate for broadcasting. For example, at network 10.31.4.0/24, it will be 10.31.4.255, and you can find various rules to calculate it. 3. Instead of using a broadcast address, you can figure our all addresses on this network and send unicast requests except to the subnet broadcast address . At most networks, it will be sending to up to 253 address, whereas rarely it could come to higher numbers. Take care, Kind regards, Robert ............................ _______________________________________________ Interest mailing list Interest@qt-project.org http://lists.qt-project.org/mailman/listinfo/interest
