/// <summary>
/// Gets NAT info from STUN server.
/// </summary>
/// <param name="host">STUN server name or IP.</param>
/// <param name="port">STUN server port. Default port is 3478.</param>
/// <param name="socket">UDP socket to use.</param>
/// <returns>Returns UDP netwrok info.</returns>
/// <exception cref="Exception">Throws exception if unexpected error happens.</exception>
internal static StunResult Query(string host, int port, Socket socket)
{
if (host == null)
{
throw new ArgumentNullException("host");
}
if (socket == null)
{
throw new ArgumentNullException("socket");
}
if (port < 1)
{
throw new ArgumentException("Port value must be >= 1 !");
}
if (socket.ProtocolType != ProtocolType.Udp)
{
throw new ArgumentException("Socket must be UDP socket !");
}
IPEndPoint remoteEndPoint = new IPEndPoint(System.Net.Dns.GetHostAddresses(host)[0], port);
socket.ReceiveTimeout = 3000;
socket.SendTimeout = 3000;
/*
* In test I, the client sends a STUN Binding Request to a server, without any flags set in the
* CHANGE-REQUEST attribute, and without the RESPONSE-ADDRESS attribute. This causes the server
* to send the response back to the address and port that the request came from.
*
* In test II, the client sends a Binding Request with both the "change IP" and "change port" flags
* from the CHANGE-REQUEST attribute set.
*
* In test III, the client sends a Binding Request with only the "change port" flag set.
*
+--------+
| Test |
| I |
+--------+
|
|
| V
| /\ /\
| N / \ Y / \ Y +--------+
| UDP <-------/Resp\--------->/ IP \------------->| Test |
| Blocked \ ? / \Same/ | II |
\ / \? / +--------+
\/ \/ |
| N |
| V
| V /\
+--------+ Sym. N / \
| Test | UDP <---/Resp\
| II | Firewall \ ? /
+--------+ \ /
| \/
| V |Y
| /\ /\ |
| Symmetric N / \ +--------+ N / \ V
| NAT <--- / IP \<-----| Test |<--- /Resp\ Open
| \Same/ | I | \ ? / Internet
\? / +--------+ \ /
\/ \/
| |Y
| |
| V
| Full
| Cone
| V /\
+--------+ / \ Y
| Test |------>/Resp\---->Restricted
| III | \ ? /
+--------+ \ /
\/
|N
| Port
+------>Restricted
|
*/
// Test I
StunMessage test1 = new StunMessage();
test1.Type = StunMessageType.BindingRequest;
StunMessage test1response = DoTransaction(test1, socket, remoteEndPoint);
// UDP blocked.
if (test1response == null)
{
return(new StunResult(StunNetType.UdpBlocked, null));
}
else
{
// Test II
StunMessage test2 = new StunMessage();
test2.Type = StunMessageType.BindingRequest;
test2.ChangeRequest = new StunChangeRequest(true, true);
// No NAT.
if (socket.LocalEndPoint.Equals(test1response.MappedAddress))
{
StunMessage test2Response = DoTransaction(test2, socket, remoteEndPoint);
// Open Internet.
if (test2Response != null)
{
return(new StunResult(StunNetType.OpenInternet, test1response.MappedAddress));
}
// Symmetric UDP firewall.
else
{
return(new StunResult(StunNetType.SymmetricUdpFirewall, test1response.MappedAddress));
}
}
// NAT
else
{
StunMessage test2Response = DoTransaction(test2, socket, remoteEndPoint);
// Full cone NAT.
if (test2Response != null)
{
return(new StunResult(StunNetType.FullCone, test1response.MappedAddress));
}
else
{
/*
* If no response is received, it performs test I again, but this time, does so to
* the address and port from the CHANGED-ADDRESS attribute from the response to test I.
*/
// Test I(II)
StunMessage test12 = new StunMessage();
test12.Type = StunMessageType.BindingRequest;
StunMessage test12Response = DoTransaction(test12, socket, test1response.ChangedAddress);
if (test12Response == null)
{
throw new Exception("STUN Test I(II) dind't get resonse !");
}
else
{
// Symmetric NAT
if (!test12Response.MappedAddress.Equals(test1response.MappedAddress))
{
return(new StunResult(StunNetType.Symmetric, test1response.MappedAddress));
}
else
{
// Test III
StunMessage test3 = new StunMessage();
test3.Type = StunMessageType.BindingRequest;
test3.ChangeRequest = new StunChangeRequest(false, true);
StunMessage test3Response = DoTransaction(test3, socket, test1response.ChangedAddress);
// Restricted
if (test3Response != null)
{
return(new StunResult(StunNetType.RestrictedCone, test1response.MappedAddress));
}
// Port restricted
else
{
return(new StunResult(StunNetType.PortRestrictedCone, test1response.MappedAddress));
}
}
}
}
}
}
}