c# - 关于 SetSocketOption & MulticastOption 的问题

Question

我在方法 Receive 之前创建了一个组并发送消息 1 行，通过创建线程等待消息。这段代码完美。我只是想知道为什么我不应该在 Send 方法中添加这一行，以便在我尝试向组发送内容之前将套接字加入组。

server.SetSocketOption(SocketOptionLevel.IP, SocketOptionName.AddMembership, MulticastOption);

using System;
using System.Net;
using System.Net.Sockets;
using System.Text;
using System.Threading;

class MAIN
{
    private static MulticastOption CreateGroup()
    {
        return new MulticastOption(IPAddress.Parse("224.100.0.1"));
    }
    private static void Receive(MulticastOption MulticastOption)
    {
        Socket sock = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp);
        IPEndPoint iep = new IPEndPoint(IPAddress.Any, 9050);
        EndPoint ep = (EndPoint)iep;
        sock.Bind(iep);
        sock.SetSocketOption(SocketOptionLevel.IP, SocketOptionName.AddMembership, MulticastOption);
        //
        byte[] data = new byte[1024];
        new Thread(new ThreadStart(Send)).Start();
        int recv = sock.ReceiveFrom(data, ref ep);
        String stringData = Encoding.ASCII.GetString(data, 0, recv);
        Console.WriteLine("received: {0} from: {1}", stringData, ep.ToString());
        sock.Close();
    }
    private static void Send()
    {
        Socket server = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp);
        IPEndPoint iep = new IPEndPoint(IPAddress.Parse("224.100.0.1"), 9050);


        byte[] data = Encoding.ASCII.GetBytes("This is a test message");
        server.SendTo(data, iep);
        server.Close();
    }
    public static void Main(String[] args)
    {
        Receive(CreateGroup());
        Console.ReadKey();
    }
}

Answer 1

来自 this article :

The IP_ADD_MEMBERSHIP option allows you to join a multicast group specified by the host group address in the multicast address structure. You must join a group to receive multicast datagrams. You do not need to join a group to send multicast datagrams.

但是，由于默认的 TTL 值，这仅适用于本地子网。参见 this article以获得更明确的答案。