NAT traversal. NAT traversal (sometimes abbreviated as NAT-T) is a general term for techniques that establish and maintain Internet protocol connections traversing network address translation (NAT) gateways, which break end-to-end connectivity. Intercepting and modifying traffic can only be performed transparently in the absence of secure encryption and authentication. NAT traversal techniques are typically required for client-to-client networking applications.[1] The majority of NAT traversal techniques fail to traverse Carrier-grade NATs which are typically Symmetric NATs.
Explanation[edit] Most NAT behavior-based techniques 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. Techniques[edit] The following NAT traversal techniques are available: Traversal across Symmetric NAT[edit] IPsec traversal across NAT[edit]
How Does NAT-T work with IPSec? Introduction: This document describes details on how NAT-T works. Background: ESP encrypts all critical information, encapsulating the entire inner TCP/UDP datagram within an ESP header. ESP is an IP protocol in the same sense that TCP and UDP are IP protocols (OSI Network Layer 3), but it does not have any port information like TCP/UDP (OSI Transport Layer 4). This is a difference from ISAKMP which uses UDP port 500 as its transport layer. PAT (Port Address Translation) is used to provide many hosts access to the internet through the same publically routable ip address. Q1: Why can't an ESP packet pass through a PAT device? It is precisely because ESP is a protocol without ports that prevents it from passing through PAT devices.
Q2: How does NAT-T work with ISAKMP/IPsec? NAT Traversal performs two tasks: Detects if both ends support NAT-T Detects NAT devices along the transmission path (NAT-Discovery) Step one occurs in ISAKMP Main Mode messages one and two. Example: References----- Routing (Networking - engineering) Carrier-grade NAT. Carrier-grade NAT (CGN), also known as large-scale NAT (LSN), is an approach to IPv4 network design in which end sites, in particular residential networks, are configured with private network addresses that are translated to public IPv4 addresses by middlebox network address translator devices embedded in the network operator's network, permitting the sharing of small pools of public addresses among many end sites.
This shifts the NAT function and configuration thereof from the customer premises to the Internet service provider network. Carrier-grade NAT has been proposed as an approach for mitigating IPv4 address exhaustion.[1] Critics of carrier-grade NAT argue the following aspects: One use scenario of CGN can be described as NAT444,[3] because some customer's connections to public servers would pass through three different IPv4 addressing domains: the customer's own private network, the carrier's private network and the public Internet. Shared address space[edit] Issues[edit] Traversal Using Relays around NAT. TURN is specified by RFC 5766. An update to TURN for IPv6 is specified in RFC 6156.
The TURN URI scheme is documented in RFC 7065. Introduction[edit] NATs, while providing many benefits, also come with many drawbacks. Session Traversal Utilities for NAT (STUN) provides one means for an application to traverse a NAT. A complete solution requires a means by which a client can obtain a transport address from which it can receive media from any peer which can send packets to the public Internet. Although TURN will almost always provide connectivity to a client, it comes at high cost to the provider of the TURN server. Protocol[edit] The process begins when a Client Computer ("Client") wants to contact a Peer Computer ("Peer") for a data transaction, but cannot do so due to both, Client and Peer, being behind respective NATs. First, the Client contacts a TURN server with an "Allocate" request.
See also[edit] Interactive Connectivity Establishment External links[edit] Yahoo! [ScreenOS] NAT Traversal overview. This article provides an overview of NAT Transversal. An overview of NAT Transversal. Note: This article is applicable to Screen OS 5.0 or later; however, NAT-T draft 2 is not supported, until Screen OS 5.1. Traditionally, IPSec does not work when traversing across a device doing NAT. To circumvent this problem, NAT-T or NAT Traversal was developed. To create a VPN from behind a NAT device, the IPSec gateway behind the NAT device and the gateway in the non-NAT environment must support NAT-T, i.e. both VPN end-points must support NAT-T.
With pre-shared keys, the network behind the NAT device needs to initiate the IPSec negotiations. After two IPSec peers agree that NAT-T is needed, IPSec packets between them will be encapsulated by one new and two extra headers such that even if the IP packet on the wire is altered by NAT device(s), there is enough information in the extra headers and SPI to recover the original IPSec packet. Original IPsec packet NAT-T encapsulated IPsec packet. [ScreenOS] NAT Traversal overview. IP NAT Address Terminology. IP NAT Address Terminology(Page 2 of 3) Combining Inside/Outside and Local/Global Address Designations This is a bit confusing, so I will try to explain further. The NAT translating router has the job of interfacing the inside network to the outside network (the Internet). Inside devices need to be able to talk to outside devices and vice-versa, but inside devices can only use addressing consistent with the local network addressing scheme. Similarly, outside devices cannot use local addressing.
Thus, both inside and outside devices can be referred to with local or global address versions. Inside Local Address: An address of a device on the local network, expressed using its normal local device representation. Let's say that device 10.0.0.207 wants to send an HTTP request to an Internet server located at address 204.51.16.12. Outside Global Address: An address of an external (public Internet) device as it is referred to on the global Internet. Phew, it's still confusing, isn't it?
Network Address Translation. Network Address Translation, defined by RFC 1631, is becoming very popular in today's networks as it's supported by almost every operating system, firewall appliance and application. NAT was born thanks to the fast depletion of public IP Addresses, in other words real IP Addresses that can only exist on the Internet. As IP Addresses are 32 Bit, in theory we could have upto 4,294,967,296 IP Addresses (that's 2^32) ! In practice though the number is a lot smaller, somewhere around 3.2 billion, because of the way the IP Addresses are separated into Classes (Class A, B , C e.t.c) and the need to set aside special addresses for multicasting (also known as Class D), broadcasting and other functions.
This exciting section will show, and explain in detail, what NAT is, its different modes and how they work. We will also see how NAT helps protect your network and minimise network security threats. So What's Covered ? With all this in mind, I've split NAT into 6 sections. Section 1: NAT Concepts. Network Address Translation (NAT) FAQ. NAT: Local and Global Definitions. Introduction This document defines and clarifies the Network Address Translation (NAT) terms of inside local, inside global, outside local, and outside global. Prerequisites Requirements There are no specific requirements for this document. Components Used This document is not restricted to specific software and hardware versions. Conventions Refer to the Cisco Technical Tips Conventions for more information on document conventions. Term Definitions Cisco defines these terms as: Inside local address—The IP address assigned to a host on the inside network. These definitions still leave a lot to be interpreted.
Local address—A local address is any address that appears on the inside portion of the network. Packets sourced on the inside portion of the network have an inside local address as the source address and an outside local address as the destination address of the packet, while the packet resides on the inside portion of the network.
This image provides an example. Examples Related Information. Network Address Translation (NAT) FAQ. Configuring NAT Overload On A Cisco Router. NAT (Network Address Translation) is a method that allows the translation (modification) of IP addresses while packets/datagrams are traversing the network. NAT Overload, also known as PAT (Port Address Translation) is essentially NAT with the added feature of TCP/UDP ports translation. The main purpose of NAT is to hide the IP address (usually private) of a client in order to reserve the public address space. For example a complete network with 100 hosts can have 100 private IP addresses and still be visible to the outside world (internet) as a single IP address.
Other benefits of NAT include security and economical usage of the IP address ranges at hand. The following steps explain basic Cisco router NAT Overload configuration. Example Scenario The diagram below represents our example network which consists of a number of internal clients and a router connected to our ISP via its serial interface. Configure NAT Overload - PAT (Port Address Translation) Verifying NAT Overload operation. NAT w/ IPTABLES. 2001:1::2/128 NAT Address (IPv6) 4. IPS Transport Layer.