How to find the destination address of a UDP packet using boost::asio?

Question

I'm developing a peer-to-peer communications network for use over a LAN in an industrial environment. Some messages are are just asynchronous, and don't require a response. Others are request-response. The request messages (and the async messages) are sent to a multicast group, and the replies to requests are sent unicast. Each endpoint, therefore, receives UDP packets that are sent to the multicast group, and also receives messages that are just sent to it using plain unicast.

So far it's working fine, but there doesn't seem to be any way in boost::asio to find out the destination address of a received UDP packet (using socket.async_receive_from) - whether it was sent to the multicast group or the actual interface. I can use the contents of the message to infer whether it was sent multicast or unicast, but it would be nice to be able to also check the destination address.

We are currently using Windows 7, but will be transitioning to Linux in the future.

Is there a way to find the destination address of a UDP packet received using boost::asio?

Answer 1

Unfortunately this is not possible with boost::asio, and usually is not "the way to do" it, as you try to access Transport Layer information at the Application Layer .

So you basically have two options:

a) Write non-portable system code with for example IP_PKTINFO or SO_BINDTODEVICE on Linux. Example Code can be found on the boost asio mailing list here

b) use two distinct sockets, one for the multicast and one for the unicast. You therefore need to specify a listen_address other than "0.0.0.0" on each socket.

udp::endpoint(address_v4::from_string("239.192.152.143"), 6771)

This Question on SO might also be helpful: Using a specific network interface for a socket in windows