UDP server send packet not over multicast ip with boost asio - boost

Question

I'm beginner with boost::asio and udp networking system.
I'm trying to receive many of packet from multicast(239.255.255.251:5353) and I want to send packet multicast(239.255.255.251:5353) for specific device.
I referenced this example from boost
http://www.boost.org/doc/libs/1_37_0/doc/html/boost_asio/example/multicast/receiver.cpp
and I modified that
void handle_receive_from(const boost::system::error_code& error,
size_t bytes_recvd)
{
if (!error)
{
if(mdns_validate_name(data_, bytes_recvd))
{
std::cout.write(data_, bytes_recvd);
std::cout << std::endl;
/** make packet for send **/
socket_.async_send_to(
boost::asio::buffer(data_, length), multi_endpoint_,
boost::bind(&receiver::handle_send, this,
boost::asio::placeholders::error,
boost::asio::placeholders::bytes_transferred));
}
else
{
socket_.async_receive_from(
boost::asio::buffer(data_, max_length), multi_endpoint_,
boost::bind(&receiver::handle_receive_from, this,
boost::asio::placeholders::error,
boost::asio::placeholders::bytes_transferred));
}
}
}
my problem is packet not over multicast(239.255.255.251:5353). it just sent specific ip(192.168.0.168). I checked wire shark.
I want to send packet again over multicast (239.255.255.251:5353).
please comment!

Answer 1

Unfortunately UDP multicast sending and receiving are completely different.
A receiver uses a local address to select the receiving device: usually set to any. Whilst a sender requires a remote address, i.e. the multicast address. In your case that would be 239.255.255.251.
E.g. from the boost::asio sender example:
class sender
{
public:
sender(boost::asio::io_service& io_service,
const boost::asio::ip::address& multicast_address)
: endpoint_(multicast_address, multicast_port),
socket_(io_service, endpoint_.protocol())
{}
.
.
.
private:
boost::asio::ip::udp::endpoint endpoint_;
boost::asio::ip::udp::socket socket_;
};
BTW the boost::asio UDP example that you reference is very old and for a receiver!
The latest boost::asio UDP sender example is here. However, for your purposes the echo server would be a better starting point.
If you want to see complete example of IPv4 and IPv6 UDP asio comms then have a look at udp_adaptor.hpp here.