java udp send from specific IP address

Question

I have a server with many IP addresses, and a UDP socket bound to 0.0.0.0 so I can receive UDP from any of them. How can I specify the source IP address to use in the UDP packets I am sending? My current implementation is using NIO so maybe using the DatagramChannel to perform the sending is the problem.

Answer 1

The following program demonstrates that your requirement is imaginary. It shows that a datagram packet originated at a DatagramSocket bound to 0.0.0.0 is delivered with a source-address of 127.0.0.1.

public static void main(String[] args) throws IOException
{
    DatagramSocket  ds1 = new DatagramSocket(0);
    int port = ds1.getLocalPort();
    System.out.println(ds1.getLocalAddress());
    DatagramSocket  ds2 = new DatagramSocket();
    byte[] bytes = {0x01};
    SocketAddress sa = new InetSocketAddress("localhost", port);
    DatagramPacket  dp = new DatagramPacket(bytes, 0, bytes.length, sa);
    ds2.send(dp);
    ds1.receive(dp);
    ds2.send(dp);
    ds2.receive(dp);
    System.out.println(dp.getAddress());
}

Answer 2

我放弃了一个干净的解决方案，只对服务器上的每个IP地址使用一个绑定的DatagramSocket，该地址可用于发送UDP以及出站数据包的特定源IP。