<![CDATA[Sending UDP packets and QUdpSocket::writeDatagram]]>Here is a snippet of code that I am using send a UDP packet. All works fine as long as the destination IP address is active. If the IP address is not active/reachable I see ARP 'who has a.b.c.d'. With UDP being connectionless I would not expect this behavior. Any comments or suggestions are welcome.

60 4.562357000 DellEsgP_e1:83:f2 Broadcast ARP 42 Who has 192.168.1.119? Tell 192.168.1.123
Thanks,

txSocket = new QUdpSocket(this); //create UDP socket to send to

txPacket.clear();
txDatagram.clear();

// Build a packet to send
txPacket.append("This is a test");
txPacket.append(" ");

//Create the datagram
txDatagram = txPacket.toUtf8(); //convert string to datagram

//Send the datagram

txSocket->writeDatagram(txDatagram.data(), txDatagram.size(), QHostAddress("192.168.1.118"), 1000);

]]>https://forum.qt.io/topic/33629/sending-udp-packets-and-qudpsocket-writedatagramRSS for NodeMon, 17 Aug 2026 19:58:32 GMTMon, 28 Oct 2013 16:34:44 GMT60<![CDATA[Reply to Sending UDP packets and QUdpSocket::writeDatagram on Thu, 31 Oct 2013 16:55:12 GMT]]>Thanks, for the reminder an layer 2 behavior.

Jay

]]>https://forum.qt.io/post/202499https://forum.qt.io/post/202499Thu, 31 Oct 2013 16:55:12 GMT<![CDATA[Reply to Sending UDP packets and QUdpSocket::writeDatagram on Thu, 31 Oct 2013 09:30:14 GMT]]>Hi,

this is the correct behaviour.

ARP means (Address Resolution Protocol); when a destination address couldn’t be resolved by ARP, the UDP packet isn’t sent. In this way the network isn’t full of no-destination packets.

UPD is a connectionless protocol, so if the destination is resolved the packet is sent regardless if there is someone ready to recevie it..

]]>https://forum.qt.io/post/202439https://forum.qt.io/post/202439Thu, 31 Oct 2013 09:30:14 GMT