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Introduction
STUN – Simple Traversal of User Datagram Protocol (UDP) through Network Address Translators (NATs). In few words, it just helps you to map your local computer IP:port to public IP:port.
STUN working idea is pretty simple. The client just sends a UDP packet out to the STUN server and the server answers back with IP:port you connected. STUN does three tests to detect the NAT type.
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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 / IP ————->| Test |
Blocked ? / Same/ | II |
/ ? / ——–
/ / |
| N |
| V
V /
——– Sym. N /
| Test | UDP
| II | Firewall ? /
——– /
| /
V |Y
/ / |
Symmetric N / ——– N / V
NAT
Same/ | I | ? / Internet
? / ——– /
/ /
| |Y
| |
| V
| Full
| Cone
V /
——– / Y
| Test |——>/Resp—->Restricted
| III | ? /
——– /
/
|N
| Port
——>Restricted
///
/// UDP is always blocked.
///
UdpBlocked,
///
/// No NAT, public IP, no firewall.
///
OpenInternet,
///
/// No NAT, public IP, but symmetric UDP firewall.
///
SymmetricUdpFirewall,
///
/// A full cone NAT is one where all requests from the same internal
/// IP address and port are mapped to the same external IP address and port.
/// Furthermore, any external host can send a packet to the internal host,
/// by sending a packet to the mapped external address.
///
FullCone,
///
/// A restricted cone NAT is one where all requests from the same
/// internal IP address and port are mapped to the same external IP address and port.
/// Unlike a full cone NAT, an external host (with IP address X)
/// can send a packet to the internal host only if the internal host
/// had previously sent a packet to IP address X.
///
RestrictedCone,
///
/// A port restricted cone NAT is like a restricted cone NAT, but the restriction
/// includes port numbers. Specifically, an external host can send a packet,
/// with source IP address X and source port P, to the internal host only if
/// the internal host had previously sent a packet to IP address X and port P.
///
PortRestrictedCone,
///
/// A symmetric NAT is one where all requests
/// from the same internal IP address and port,
/// to a specific destination IP address and port, are mapped to the same external
/// IP address and port. If the same host sends a packet with the same source address
/// and port, but to a different destination, a different mapping is used.
/// Furthermore, only the external host that
/// receives a packet can send a UDP packet back to the internal host.
///
Symmetric
Using the Code
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//Create new socket for STUN client.Socket socket = new Socket
(AddressFamily.InterNetwork,SocketType.Dgram,ProtocolType.Udp);
socket.Bind(new IPEndPoint(IPAddress.Any,0));
//Query STUN serverSTUN_Result result = STUN_Client.Query(“stunserver.org”,3478,socket);
if(result.NetType != STUN_NetType.UdpBlocked){
//UDP blocked or !!!! bad STUN server}
else{
IPEndPoint publicEP = result.PublicEndPoint;
//Do your stuff}
发布者：全栈程序员栈长，转载请注明出处：https://javaforall.cn/160521.html原文链接：https://javaforall.cn
