问题
I want to check if the upd port for OpenVPN is open. For Tcp Port it was really simple, but now I struggle with Udp ports.
This is my TCP Implementation
private static bool TestConnectionInternal(string hostname, int port, int timeOutMs, int maxTries, int count)
{
using (var tcpClient = new TcpClient())
{
try
{
Task result = tcpClient.ConnectAsync(hostname, port);
return result.Wait(timeOutMs);
}
catch (Exception e)
{
count += 1;
if (count < maxTries)
{
return TestConnectionInternal(hostname, port, timeOutMs, maxTries, count);
}
return false;
}
}
}
回答1:
Simple check OpenVPN UDP service (except that one uses --tls-auth or --secret)
bool CheckOpenVPNudp(string ip, int port)
{
IPEndPoint RemoteEndPoint = new IPEndPoint(IPAddress.Parse(ip), port);
Socket server = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp);
byte[] data = { 56, 1, 0, 0, 0, 0, 0, 0, 0 }; //OpenVPN client welcome datagram
server.SendTo(data, data.Length, SocketFlags.None, RemoteEndPoint);
server.ReceiveTimeout = 15000; //15 seconds timeout
EndPoint Remote = (EndPoint)(RemoteEndPoint);
try
{
byte[] answer = new byte[1024];
int recv = server.ReceiveFrom(answer, ref Remote);
Console.WriteLine("Message received from {0}:", Remote.ToString());
Console.WriteLine(System.Text.Encoding.ASCII.GetString(answer, 0, recv));
return true;
}
catch (Exception e)
{
Console.WriteLine(e.Message);
return false;
}
}
回答2:
There no way to know if a UDP port is open. If you lucky you get a icmp unreachable port closed negative answer. For some protocols like NTP you can try to send a valid query and check for a response. If OpenVPN is configured with --tls-auth or --secret you cannot produce a valid packet to trigger a repsonse if you don know the secret key.
来源：https://stackoverflow.com/questions/21462339/check-if-openvpn-udp-port-is-open