网络切换后UDP广播失效问题排查求助

前置条件 #

• PC1（Windows系统）：
  • LAN地址：10.0.1.11
  • WiFi地址：10.0.1.10
• PC2（Windows系统）：
  • WiFi地址：10.0.1.4

操作步骤及现象 #

1. 禁用PC1的WiFi，启用LAN，确认IP地址为10.0.1.11；
2. 启用PC2的WiFi，确认IP地址为10.0.1.4；
3. 在PC1上启动UDP广播程序（可接收同LAN内其他PC的UDP应答包），在PC2上启动UDP接收器（接收广播消息后会回复发送方）；
4. 在PC1上启动Wireshark捕获网络包；
5. 确认PC1收到来自PC2的应答消息；
6. 在UDP广播程序运行期间，禁用PC1的LAN并启用WiFi，确认IP地址切换为WiFi接口的10.0.1.10；
7. 一段时间后发现PC1无法收到PC2的UDP应答，通过Wireshark也未捕获到PC1发送的任何广播包（无论使用过滤规则ip.proto==UDP && ip.src==10.0.1.10还是ip.proto==UDP && ip.src==10.0.1.11）；
8. 查看PC1的UDP接收器日志，发现异常现象：PC1从LAN切换到WiFi后，日志中出现已禁用的LAN接口IP（10.0.1.11）响应广播的记录。

广播消息发送代码 #

Socket sendSocket = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp);

// Use GetHostAddresses() to enumerate the local IPAddress
string hostName = Dns.GetHostName();
var addressList = Dns.GetHostAddresses(hostName);
foreach (var ip in addressList)
{
    if (ip.AddressFamily != AddressFamily.InterNetwork) { continue; }
    IPEndPoint ep = null;
    IPAddress ipSend = null;
    ipSend = IPAddress.Parse(ip.ToString());
    ipSend.Address |= 0xFF000000;
    ep = new IPEndPoint(ipSend, 1020);
    sendSocket.SendTo(broadcastMessage, ep);
}

//Use GetAllNetworkInterfaces() to enumerate the local IPAddress
NetworkInterface[] nics = NetworkInterface.GetAllNetworkInterfaces();
foreach (NetworkInterface adapter in nics)
{
  if (adapter.NetworkInterfaceType == NetworkInterfaceType.Ethernet ||
      adapter.NetworkInterfaceType == NetworkInterfaceType.Wireless80211)
  {
    IPInterfaceProperties ip = adapter.GetIPProperties();
    UnicastIPAddressInformationCollection ipCollection = ip.UnicastAddresses;
    foreach (UnicastIPAddressInformation ipadd in ipCollection)
    {
      if (ipadd.Address.AddressFamily == AddressFamily.InterNetwork)
      {
        IPEndPoint ep = null;
        IPAddress ipSend = null;
        ipSend = IPAddress.Parse(ipadd.Address.ToString());
        ipSend.Address |= 0xFF000000;
        ep = new IPEndPoint(ipSend, 1020);
        sendSocket.SendTo(broadcastMessage, ep);
      }
    }
  }
}

//Use GetHostEntry() to enumerate the local IPAddress
IPHostEntry host = Dns.GetHostEntry(hostName, AddressFamily.InterNetwork);
foreach (var ip in host.AddressList)
{
  IPEndPoint ep = null;
  IPAddress ipSend = null;
  ipSend = IPAddress.Parse(ip.ToString());
  ipSend.Address |= 0xFF000000;
  ep = new IPEndPoint(ipSend, 1020);
  sendSocket.SendTo(broadcastMessage, ep);
}

我尝试了上述3种枚举本地IP地址并生成广播地址的方法，但均未生效。

看起来，网络从LAN切换到WiFi后，调用SendTo() API发送的广播消息并未通过PC1的TCP/IP协议栈（否则Wireshark应能捕获到相关数据包）。

求问针对该问题有什么排查思路或解决方案？

UDP接收器代码 #

socket = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp);
socket.SetSocketOption(SocketOptionLevel.Socket, SocketOptionName.ReuseAddress, 1);
socket.Bind(new IPEndPoint(IPAddress.Any, 1020));
socket.ReceiveTimeout = 100;
_udpReceiver = new UdpClient{Client = socket};
_udpReceiver.Client.ReceiveBufferSize = 1024 * 1024;

endPoint = new IPEndPoint(IPAddress.Any, 0);
while (!_stopReceiveEvent.WaitOne(1))
{
  byte[] rawBytes = _udpReceiver.Receive(ref endPoint);
  if (rawBytes.Length <= 0){ continue; }
  string receivedDeviceIPAddr = endPoint.Address.ToString();
  Console.WriteLine($"Recieve UDP response from {receivedDeviceIPAddr} : {endPoint.Port}");        
}

内容的提问来源于stack exchange，提问作者chaingun