stun client java实现_STUN Client

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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}