我希望借助具有静态IP的服务器与两个客户端进行UDP打孔.服务器在端口7070和7071上等待两个客户端.之后,它会相互发送IP地址和端口.这部分工作正常.但是我无法在两个客户之间建立通信.我在不同的Wifi网络和3G移动网络中尝试了代码.客户端程序抛出IO-Exception“无路由到主机”.
客户端代码用于两个客户端.一旦用7070端口执行,一次用7071执行.

您认为我是否正确实施了UDP打孔概念？有什么想法让它发挥作用？
这是服务器代码,然后是客户端代码.

谢谢你的帮助.

服务器代码：

public class UDPHolePunchingServer {

    public static void main(String args[]) throws Exception {

    // Waiting for Connection of Client1 on Port 7070
    // ////////////////////////////////////////////////

    // open serverSocket on Port 7070
    DatagramSocket serverSocket1 = new DatagramSocket(7070);

    System.out.println("Waiting for Client 1 on Port "
            + serverSocket1.getLocalPort());

    // receive Data
    DatagramPacket receivePacket = new DatagramPacket(new byte[1024], 1024);
    serverSocket1.receive(receivePacket);

    // Get IP-Address and Port of Client1
    InetAddress IPAddress1 = receivePacket.getAddress();
    int port1 = receivePacket.getPort();
    String msgInfoOfClient1 = IPAddress1 + "-" + port1 + "-";

    System.out.println("Client1: " + msgInfoOfClient1);

    // Waiting for Connection of Client2 on Port 7071
    // ////////////////////////////////////////////////

    // open serverSocket on Port 7071
    DatagramSocket serverSocket2 = new DatagramSocket(7071);

    System.out.println("Waiting for Client 2 on Port "
            + serverSocket2.getLocalPort());

    // receive Data
    receivePacket = new DatagramPacket(new byte[1024], 1024);
    serverSocket2.receive(receivePacket);

    // GetIP-Address and Port of Client1
    InetAddress IPAddress2 = receivePacket.getAddress();
    int port2 = receivePacket.getPort();
    String msgInfoOfClient2 = IPAddress2 + "-" + port2 + "-";

    System.out.println("Client2:" + msgInfoOfClient2);

    // Send the Information to the other Client
    // /////////////////////////////////////////////////

    // Send Information of Client2 to Client1
    serverSocket1.send(new DatagramPacket(msgInfoOfClient2.getBytes(),
            msgInfoOfClient2.getBytes().length, IPAddress1, port1));

    // Send Infos of Client1 to Client2
    serverSocket2.send(new DatagramPacket(msgInfoOfClient1.getBytes(),
            msgInfoOfClient1.getBytes().length, IPAddress2, port2));

    //close Sockets
    serverSocket1.close();
    serverSocket2.close();
}

客户代码

public class UDPHolePunchingClient {

    public static void main(String[] args) throws Exception {
    // prepare Socket
    DatagramSocket clientSocket = new DatagramSocket();

    // prepare Data
    byte[] sendData = "Hello".getBytes();

    // send Data to Server with fix IP (X.X.X.X)
    // Client1 uses port 7070, Client2 uses port 7071
    DatagramPacket sendPacket = new DatagramPacket(sendData,
            sendData.length, InetAddress.getByName("X.X.X.X"), 7070);
    clientSocket.send(sendPacket);

    // receive Data ==> Format:"<IP of other Client>-<Port of other Client>"
    DatagramPacket receivePacket = new DatagramPacket(new byte[1024], 1024);
    clientSocket.receive(receivePacket);

    // Convert Response to IP and Port
    String response = new String(receivePacket.getData());
    String[] splitResponse = response.split("-");
    InetAddress ip = InetAddress.getByName(splitResponse[0].substring(1));

    int port = Integer.parseInt(splitResponse[1]);

    // output converted Data for check
    System.out.println("IP: " + ip + " PORT: " + port);

    // close socket and open new socket with SAME localport
    int localPort = clientSocket.getLocalPort();
    clientSocket.close();
    clientSocket = new DatagramSocket(localPort);

    // set Timeout for receiving Data
    clientSocket.setSoTimeout(1000);

    // send 5000 Messages for testing
    for (int i = 0; i < 5000; i++) {

        // send Message to other client
        sendData = ("Datapacket(" + i + ")").getBytes();
        sendPacket = new DatagramPacket(sendData, sendData.length, ip, port);
        clientSocket.send(sendPacket);

        // receive Message from other client
        try {
            receivePacket.setData(new byte[1024]);
            clientSocket.receive(receivePacket);
            System.out.println("REC: "
                    + new String(receivePacket.getData()));

        } catch (Exception e) {
            System.out.println("SERVER TIMED OUT");
        }
    }

    // close connection
    clientSocket.close();
}

UPDATE
代码通常有效.我现在已经在两个不同的家庭网络中尝试了它并且它正在工作.但它不适用于我的3G或大学网络.在3G中,我验证了NAT正在将两个端口(客户端端口和路由器分配的端口)再次映射到一起,即使在关闭并打开clientSocket之后也是如此.有谁知道为什么它不工作呢？

解决方法:

所有类型的NAT都无法实现UDP打孔.没有为所有类型的NAT定义通用或可靠的方法.对称NAT甚至非常困难.

根据NAT行为,发送UDP数据包的不同设备的端口映射可能不同.
比如,如果A向B发送UDP数据包,它可能会得到一些类似50000的端口.但是如果A向C发送UDP数据包,那么它可能会获得不同的映射,如50002.因此,在您的情况下,向服务器发送数据包可能给客户端一些端口但是向其他客户端发送数据包可能会给其他端口.

您将在此处阅读有关NAT行为的更多信息：

http://tools.ietf.org/html/rfc4787

https://tools.ietf.org/html/rfc5128

UDP hole punching not going through on 3G