Question

I have a server that gathers information and broadcasts some messages across the local network. I’m using boost::asio to broadcast these via UDP on port 8079 and I can verify with WireShark that these packets are actually broadcasted as intended.

Now, naturally, I want to follow up with a listener that can react to these messages, but I am struggling to receive anything. My current approach is:

boost::asio::io_service io_service;
boost::asio::ip::udp::socket socket(io_service);
boost::asio::ip::udp::endpoint local(
    boost::asio::ip::address::from_string("192.168.2.102"),
    8079);
boost::system::error_code error;

std::cout << "Local bind: " << local << std::endl;

socket.open(boost::asio::ip::udp::v4(), error);
if(!error) {
    socket.bind(local);
    boost::array<char, 2048> buf;
    boost::asio::ip::udp::endpoint server;
    std::cout << "Listening..." << std::endl;
    while(true) {
        size_t len = socket.receive_from(boost::asio::buffer(buf), server);
        std::cout << "Received data:" << std::endl;
        std::cout.write(buf.data(), len);
        std::cout << std::endl;
    }
}

But I never receive anything. Using the debugger, I found that I’m just stuck in receive_from forever, and I don’t know why.

Some further information (mostly from Wireshark) that I’m not sure about whether it could be causing these problems: Server and client are running on the same machine. The server is sending a sending an 88 bytes message every two seconds from port 34050 (source) to 8079 (destination). 192.168.2.102 is the ip of the machine within the local network.

Answer 1

IIRC, you have to bind to INADDR_ANY to receive broadcast packets. There are quite a few discussions in Linux message lists discussing this issue. Beyond this, make sure that the netmask matches on both computers. If the broadcast is going to 192.168.255.255 and your client netmask is 255.255.255.0, you will not receive the packets.