I am not a specialist in TCP/UDP communications, but I am trying to implement some communications using UDP packets (v6). I can't use anything else than UDP v6 due to external constraints. I am using boost 1.37. I tried boost 1.40, same problem (see below) I have implemented a first architecture, working like : - a server listens to UDP packets v6 coming on a port ( let's say 65000). - a client connects to that port by sending a UDP packet. - the server starts a new thread, which listens for udpv6 packets on another port - the client should deconnect and reconnect to that other port. Cleitns starts opening the first socket like that : boost::asio::io_service io_service; udp::endpoint endpoint; udp::socket socket(io_service); udp::resolver::query query(udp::v6(), m_host, m_port); udp::resolver resolver(io_service); endpoint = *resolver.resolve(query); socket.open(udp::v6()); Then a function is called that sends a packet, receive an answer, etc... WORKS ! Then, I would like that socket being closed, and reopened on the same host, but on a different port. Something like this : socket.close(); udp::socket socket(io_service); udp::resolver::query query2(udp::v6(), m_host, NEWPORT); udp::resolver resolver2(io_service); endpoint = *resolver2.resolve(query2); socket.open(udp::v6()); But it fails miserably, throwing exception "Host not found (Authoritative)" on this second attempt. m_host is the ipv6 loopback address, "::1". I tried declaring at the same time, a full new set of io_service, endpoint, socket, query, resolver : the very same thing happens ! That said, there is another thread listening on the NEWPORT for udp v6 packets. I am developping mainly under linux, using lsof lists exactly the right number of ports opened (m_port and NEWPORT are opened for udpv6) So what is incorrect ? I don't really understand the behavior and complexity of io_service, maybe that's the problem ? How can I reopen a second socket on another port ? That port being listed by the system as opened succesfully, I really think the problem lies in that section. Thank you !