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NAT traversal GudangMovies21 Rebahinxxi LK21
Network address translation traversal is a computer networking technique of establishing and maintaining Internet Protocol connections across gateways that implement network address translation (NAT).
NAT traversal techniques are required for many network applications, such as peer-to-peer file sharing and voice over IP.
Network address translation
Network address translation typically uses private IP addresses on private networks with a single public IP address for the router facing the Internet. The network address translator changes the source address in network protocols for outgoing requests from that of an internal device to its external address, so that internal devices can communicate with hosts on the external network, while relaying replies back to the originating device.
This leaves the internal network ill-suited for hosting services, as the NAT device has no automatic method for determining the internal host for which incoming packets from the external network are destined. This is not a problem for general web access and email. However, applications such as peer-to-peer file sharing, VoIP services, and video game consoles require clients to be servers as well. Incoming requests cannot be easily correlated to the proper internal host. Furthermore, many of these types of services carry IP address and port number information in the application data, potentially requiring substitution with deep packet inspection.
Network address translation technologies are not standardized. As a result, the methods used for NAT traversal are often proprietary and poorly documented. Many traversal techniques require assistance from servers outside of the masqueraded network. Some methods use the server only when establishing the connection, while others are based on relaying all data through it, which increases the bandwidth requirements and latency, detrimental to real-time voice and video communications.
NAT traversal techniques usually bypass enterprise security policies. Enterprise security experts prefer techniques that explicitly cooperate with NAT and firewalls, allowing NAT traversal while still enabling marshalling at the NAT to enforce enterprise security policies. IETF standards based on this security model are Realm-Specific IP (RSIP) and middlebox communications (MIDCOM).
Techniques
Various NAT traversal techniques have been developed:
NAT Port Mapping Protocol (NAT-PMP) is a protocol introduced by Apple as an alternative to IGDP.
Port Control Protocol (PCP) is a successor of NAT-PMP.
UPnP Internet Gateway Device Protocol (UPnP IGD) is supported by many small NAT gateways in home or small office settings. It allows a device on a network to ask the router to open a port.
Interactive Connectivity Establishment (ICE) is a complete protocol for using STUN and/or TURN to do NAT traversal while picking the best network route available. It fills in some of the missing pieces and deficiencies that were not mentioned by STUN specification.
Session Traversal Utilities for NAT (STUN) is a standardized set of methods and a network protocol for NAT hole punching. It was designed for UDP but was also extended to TCP.
Traversal Using Relays around NAT (TURN) is a relay protocol designed specifically for NAT traversal.
NAT hole punching is a general technique that exploits how NATs handle some protocols (for example, UDP, TCP, or ICMP) to allow previously blocked packets through the NAT.
UDP hole punching
TCP hole punching
ICMP hole punching
Socket Secure (SOCKS) is a technology created in the early 1990s that uses proxy servers to relay traffic between networks or systems.
Application-level gateway (ALG) techniques are a component of a firewall or NAT that provides configureable NAT traversal filters. It is claimed that this technique creates more problems than it solves.
= Symmetric NAT
=
The recent proliferation of symmetric NATs has reduced NAT traversal success rates in many practical situations, such as for mobile and public WiFi connections. Hole punching techniques, such as STUN and ICE, fail in traversing symmetric NATs without the help of a relay server, as is practiced in TURN. Techniques that traverse symmetric NATs by attempting to predict the next port to be opened by each NAT device were discovered in 2003 by Yutaka Takeda at Panasonic Communications Research Laboratory and in 2008 by researchers at Waseda University. Port prediction techniques are only effective with NAT devices that use known deterministic algorithms for port selection. This predictable yet non-static port allocation scheme is uncommon in large scale NATs such as those used in 4G LTE networks and therefore port prediction is largely ineffective on those mobile broadband networks.
IPsec
IPsec virtual private network clients use NAT traversal in order to have Encapsulating Security Payload packets traverse NAT. IPsec uses several protocols in its operation which must be enabled to traverse firewalls and network address translators:
Internet Key Exchange (IKE) – User Datagram Protocol (UDP) port 500
Encapsulating Security Payload (ESP) – IP protocol number 50
Authentication Header (AH) – IP protocol number 51
IPsec NAT traversal – UDP port 4500, if and only if NAT traversal is in use
Many routers provide explicit features, often called IPsec Passthrough.
In Windows XP, NAT traversal is enabled by default, but in Windows XP with Service Pack 2 it has been disabled by default for the case when the VPN server is also behind a NAT device, because of a rare and controversial security issue. IPsec NAT-T patches are also available for Windows 2000, Windows NT and Windows 98.
NAT traversal and IPsec may be used to enable opportunistic encryption of traffic between systems. NAT traversal allows systems behind NATs to request and establish secure connections on demand.
Hosted NAT traversal (HNT) is a set of mechanisms, including media relaying and latching, that is widely used by communications providers for historical and practical reasons. The IETF advises against using latching over the Internet and recommends ICE for security reasons.
IETF standards documents
RFC 1579 – Firewall Friendly FTP
RFC 2663 – IP Network Address Translator (NAT) Terminology and Considerations
RFC 2709 – Security Model with Tunnel-mode IPsec for NAT Domains
RFC 2993 – Architectural Implications of NAT
RFC 3022 – Traditional IP Network Address Translator (Traditional NAT)
RFC 3027 – Protocol Complications with the IP Network Address Translator (NAT)
RFC 3235 – Network Address Translator (NAT)-Friendly Application Design Guidelines
RFC 3715 – IPsec-Network Address Translation (NAT) Compatibility
RFC 3947 – Negotiation of NAT-Traversal in the IKE
RFC 5128 – State of Peer-to-Peer (P2P) Communication across Network Address Translators (NATs)
RFC 5245 – Interactive Connectivity Establishment (ICE): A Protocol for Network Address Translator (NAT) Traversal for Offer/Answer Protocols
See also
Session border controller (SBC)
Port forwarding
References
External links
Problems and fact about modern day NAT traversal systems
Autonomous NAT traversal – NAT to NAT communication without a third party
Cornell University – Characterization and Measurement of TCP Traversal through NATs and Firewalls
Columbia University – An Analysis of the Skype Peer-to-Peer Internet Telephony
Peer to peer communication across Network Address Translators (UDP Hole Punching)
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Generally, players with NAT Type D are only able to connect to players with NAT Type A. If this is your NAT type, use our troubleshooting to try and improve your network's NAT type . If you would like to continue troubleshooting your network, please contact your Internet Service Provider (ISP) or network administrator for further assistance ...
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Nat Traversal also known as UDP encapsulation allows traffic to get to the specified destination when a device does not have a public address. This is usually the case if your ISP is doing NAT, or the external interface of your firewall is connected to a device that has NAT enabled.As well as IPSec providing confidentiality, it also provides ...
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The default value of TCP MSS on Cisco ASA is (if i remember correctly) 1380, and i got issues with a dual stack NAT-T IKEv2 IPSEC VPN over a PPPoE connection(not with IPv4, but woth IPV6 travelling through the tunnel) ...
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Check your NAT type and complete troubleshooting based on what type your network is. See our online match-making troubleshooting steps for these steps. Situation not resolved. If connecting to a different network resolved the issue, there is likely something preventing peer to peer connections on your original network.
Important: While troubleshooting NAT related issues, it is recommend that you test your Internet connection after making any changes to the settings of your network to determine if the change improved your network's NAT type.
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Firewall Traversal Concept . How the Firewall Traversal Concept works, and how it is possible to bypass the stateful function of firewall to initiate inbound calls, in other words, connection initiated from lower security level to higher security with the integration of the Cisco Expressway series, how the SIP invite is proxied through the Cisco Expressway Core and Edge, and very …
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Another option is to do NAT Traversal/Transparency (NAT-T). In this case the ESP traffic is tunneled inside of UDP (typically over UDP port 4500), which then allows the NAT process of the border router to uniquely identify the flow based on the source address, source UDP port, destination address, and destination UDP port, even if two inside ...
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NAT Traversal in vpn - Cisco Learning Network
To solve that issue, we use NAT-T which causes the device to encapsulate the ESP packets into a UDP packets using the port 4500, by doing so the PAT device would be able to associate a random port to port 4500 when it creates the NAT entry. NAT-T is enabled by default on Cisco IOS devices and ASAs. Regards | Aref.
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Application Layer Gateway ALG was in the past developped to provice NAT Traversal Solution in VOIP environment. Some Cisco Routers and ASA Firewall support ALG to allow voip traffic to traverse NAT allowing two endpoints to negociate the L3/L4 informations inside the SIP payload in order to establish later media or point-to-point Flow RTP.
