NAT/Firewall穿越技术

常见的NAT种类 Full Cone Restricted Cone Port Restricted Cone Symmetric NAT

Full Cone

Restricted Cone(1/2)

Restricted Cone(2/2)

Port Restricted Cone

Symmetric NAT

NAT Detection Flow

防火牆造成的問題

NAT 造出的问题

NAT/Firewall穿越技术 IPV6(Internet Protocol Version 6) UPnP(Universal Plug and Play) TRUN(Traversal Using Relay NAT) ALG(Application Layer Gatewqy) ICE(Interactive Connectivity Establish) STUN(Simple Traversal of UDP Through Netwoek Address Translators)

UPnP Universal Plug and Play It's being pushed by Microsoft A UPnP-aware client can ask the UPnP-enabled NAT how it would map a particular IP:port through UPnP

UPnP Operation

STUN(1/2) Simple Traversal of UDP Through Network Address Translators 需要在NAT外部架设 STUN Server Client 端需有特殊的 STUN Client 功能 无法穿透 symmetric NAT 未来将被ICE整合

STUN(2/2)

TURN(1/2) Traversal Using Relay NAT 主要是为了解決 symmetric NATs 必须要架設 TURN Server 未来也将被包含进 ICE

TURN(2/2)

SIP using STUN User Agent 1 STUN Server Registrar/Proxy User Agent 2 1 STUN SharedSecretRequest/TLS 9 100 Trying User Agent 1 10.2.1.1 STUN Server Registrar/Proxy User Agent 2 7 INVITE Contact:UA1@192.0.2.101 10 200 OK NAT 192.0.2.101 2 STUN SharedSecretResponse/TLS 3 STUN BindingtRequest/UDP 4 STUN BindingResponse/UDP 6 200 OK 5 REGISTER Contact:UA1@192.0.2.101 8 INVITE Contact:UA1@192.0.2.101 11 200 OK 12 ACK 13 ACK RTP Media Session

SIP using TURN User Agent 1 STUN/TURN Svr 1 STUN/TURN Svr 2 10.2.1.1 STUN/TURN Svr 1 STUN/TURN Svr 2 User Agent 2 192.168.1.1 NAT 1 NAT 2 1 STUN Requests 2 STUN Responses 3 STUN Requests 4 STUN Responses 7 180 Ringing 8 200 OK 9 ACK 12 Peer-to-Peer STUN Responses 11 Peer-to-Peer STUN Requests 14 Peer-to-Peer STUN Responses 13 Peer-to-Peer STUN Requests RTP Media Session Established using Derived Transport Addresses Proxy 5 INVITE 6 INVITE 10 ACK

ALG(1/2) Application Layer gateway It Understands the signalling messages and their relationship with the resulting media flows. It can modify the signalling to reflect the public IP address and ports being used by singalling and media traffic.

ALG(2/2)

ICE Interactive Connectivity Establishment 非 protocol 而是 framework 主要技术包括：STUN, TRUN, SIP 目前仍在RFC草案讨论阶段