NAT 类型及检测方法
NAT 类型及检测方法
STUN协议是一个客户机/服务器协议,在公网上存在着大量的STUN服务器,用户可以通过在自己主机上运行STUN客户端远程连接STUN服务器来确认自身的网络状况.
客户端主机所在网络可以分为以下类型:
1, Opened: 即主机拥有公网IP,并且没有防火墙,可自由与外部通信.
2, Full Cone NAT: 主机前有NAT设备,NAT规则如下:从主机UDP端口A发出的数据包都会对应到NAT设备出口IP的端口B,并且从任意外部地址发送到该NAT设备UDP端口B的包都会被转到主机端口A.
3, Restricted cone NAT: 主机前有NAT设备,NAT规则如下:从主机UDP端口A发出的数据包都会对应到NAT设备出口IP的端口B,但只有从之前该主机发出包的目的IP发出到该NAT设备UDP端口B的包才会被转到主机端口A.
4, Port Restricted cone NAT: 主机前有NAT设备,NAT规则如下:从主机UDP端口A发出的数据包都会对应到NAT设备出口IP的端口B,但只有从之前该主机发出包的目的IP/PORT发出到该NAT设备UDP端口B的包才会被转到主机端口A.
5, Symmetric UDP Firewall: 主机出口处没有NAT设备,但有防火墙,且防火墙规则如下:从主机UDP端口A发出的数据包保持源地址,但只有从之前该主机发出包的目的IP/PORT发出到该主机端口A的包才能通过防火墙.
6, Symmetric NAT: 主机前有NAT设备,NAT规则如下:即使数据包都从主机UDP端A发出,但只要目的地址不同,NAT设备就会为之分配不同的出端口B.
7, Blocked: 防火墙限制UDP通信.
/// <summary>
/// Specifies UDP network type.
/// </summary>
public enum STUN_NetType
{
/// <summary>
/// UDP is always blocked.
/// </summary>
UdpBlocked,
/// <summary>
/// No NAT, public IP, no firewall.
/// </summary>
OpenInternet,
/// <summary>
/// No NAT, public IP, but symmetric UDP firewall.
/// </summary>
SymmetricUdpFirewall,
/// <summary>
/// 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.
/// </summary>
FullCone,
/// <summary>
/// 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.
/// </summary>
RestrictedCone,
/// <summary>
/// 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.
/// </summary>
PortRestrictedCone,
/// <summary>
/// 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.
/// </summary>
Symmetric
}
测试过程
STUN服务器运行在UDP协议之上,它具有两个固定公网地址,能完成以下几个功能:
1. 告诉STUN客户端经NAT设备映射后的公网地址.
2. 根据STUN客户端的要求,从服务器的其他不同IP或端口向客户端回送包.
如何根据STUN服务器提供的功能来确认网络类型呢? rfc3489给出了如下图过程:
+--------+ | 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 Figure 2: Flow for type discovery process
这个过程可概括如下:
1, STUN客户端向STUN服务器发送请求,要求得到自身经NAT映射后的地址:
a,收不到服务器回复,则认为UDP被防火墙阻断,不能通信,网络类型:Blocked.
b,收到服务器回复,对比本地地址,如果相同,则认为无NAT设备,进入第2步,否则认为有NAT设备,进入3步.
2, (已确认无NAT设备)STUN客户端向STUN服务器发送请求,要求服务器从其他IP和PORT向客户端回复包:
a,收不到服务器从其他IP地址的回复,认为包被前置防火墙阻断,网络类型:Symmetric UDP Firewall.
b,收到则认为客户端处在一个开放的网络上,网络类型:Opened.
3, (已确认存在NAT设备)STUN客户端向STUN服务器发送请求,要求服务器从其他IP和PORT向客户端回复包:
a,收不到服务器从其他IP地址的回复,认为包被前置NAT设备阻断,进入第4步.
b,收到则认为NAT设备类型为Full Cone,即网络类型:Full Cone NAT.
4, STUN客户端向STUN服务器的另外一个IP地址发送请求,要求得到自身经NAT映射后的地址,并对比之:
a,地址不相同,则网络类型:Symmetric NAT.
b,相同则认为是Restricted NAT,进入第5步,进一步确认类型.
5, (已确认Restricted NAT设备)STUN客户端向STUN服务器发送请求,要求服务器从相同IP的其他PORT向客户端回复包:
a,收不到服务器从其他PORT地址的回复,认为包被前置NAT设备阻断,网络类型:Port Restricted cone NAT.
b,收到则认为网络类型: Restricted cone NAT.
免费可用的 Stun Server:
stun.ekiga.net
stun.stunprotocol.org
larry.gloo.net
几个NAT类型检查工具:
http://midcom-p2p.sourceforge.net/
http://www.9ht.com/xz/50176.html
http://download.csdn.net/download/delver2235/8109891