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62-773: LEAF is capable of running a powerful NAT firewall with several ancillary services on computer hardware generally considered obsolete, such as 486 workstations with no hard disk. LEAF is intended to work well with read-only storage media , such as write-protected floppy drives or optical discs . Distribution sizes range from a single floppy disk to several hundred megabytes. LEAF distributions typically include software designed to be economical in executable size, such as uClibc , BusyBox , Dropbear , and Shorewall . LEAF's origins lie in Debian Sarge , though many boot processes and daemon control mechanisms have been modified heavily. This Linux-distribution -related article

124-677: A group of public IP addresses. NAT hairpinning , also known as NAT loopback or NAT reflection , is a feature in many consumer routers where a machine on the LAN is able to access another machine on the LAN via the external IP address of the LAN/router (with port forwarding set up on the router to direct requests to the appropriate machine on the LAN). This notion is officially described in 2008, RFC   5128 . The following describes an example network: If

186-451: A patch available to enable RFC 4787 support but this has not yet been merged. The NAT traversal problem arises when peers behind different NATs try to communicate. One way to solve this problem is to use port forwarding . Another way is to use various NAT traversal techniques. The most popular technique for TCP NAT traversal is TCP hole punching . TCP hole punching requires the NAT to follow

248-512: A Symmetric NAT as having an Address- and Port-Dependent Mapping . For the second bullet in each row of the above table, RFC 4787 would also label Full-Cone NAT as having an Endpoint-Independent Filtering , Restricted-Cone NAT as having an Address-Dependent Filtering , Port-Restricted Cone NAT as having an Address and Port-Dependent Filtering , and Symmetric NAT as having either an Address-Dependent Filtering or Address and Port-Dependent Filtering . Other classifications of NAT behavior mentioned in

310-468: A checksum that covers all the data they carry, as well as the TCP or UDP header, plus a pseudo-header that contains the source and destination IP addresses of the packet carrying the TCP or UDP header. For an originating NAT to pass TCP or UDP successfully, it must recompute the TCP or UDP header checksum based on the translated IP addresses, not the original ones, and put that checksum into the TCP or UDP header of

372-490: A methodology for testing a device accordingly. However, these procedures have since been deprecated from standards status, as the methods are inadequate to correctly assess many devices. RFC 5389 standardized new methods in 2008 and the acronym STUN now represents the new title of the specification: Session Traversal Utilities for NAT . It is similar to an address restricted cone NAT, but the restriction includes port numbers. Many NAT implementations combine these types, so it

434-673: A network was moved, or when the upstream Internet service provider was replaced but could not route the network's address space. It has become a popular and essential tool in conserving global address space in the face of IPv4 address exhaustion . One Internet-routable IP address of a NAT gateway can be used for an entire private network . As network address translation modifies the IP address information in packets, NAT implementations may vary in their specific behavior in various addressing cases and their effect on network traffic. Vendors of equipment containing NAT implementations do not commonly document

496-476: A one-to-one translation of IP addresses (RFC 1631). RFC   2663 refers to this type of NAT as basic NAT , also called a one-to-one NAT . In this type of NAT, only the IP addresses, IP header checksum , and any higher-level checksums that include the IP address are changed. Basic NAT can be used to interconnect two IP networks with incompatible addresses. Most network address translators map multiple private hosts to one publicly exposed IP address. Here

558-399: A packet is sent to 203.0.113.1 by a computer at 192.168.1.100 , the packet would normally be routed to the default gateway (the router) A router with the NAT loopback feature detects that 203.0.113.1 is the address of its WAN interface, and treats the packet as if coming from that interface. It determines the destination for that packet, based on DNAT (port forwarding) rules for

620-405: A private network. When a computer on the private (internal) network sends an IP packet to the external network, the NAT device replaces the internal source IP address in the packet header with the external IP address of the NAT device. PAT may then assign the connection a port number from a pool of available ports, inserting this port number in the source port field. The packet is then forwarded to

682-519: A section in the menu for deleting cookies. Finer-grained management of cookies usually requires a browser extension . The first web browser, called WorldWideWeb , was created in 1990 by Sir Tim Berners-Lee . He then recruited Nicola Pellow to write the Line Mode Browser , which displayed web pages on dumb terminals . The Mosaic web browser was released in April 1993, and was later credited as

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744-646: A single local port with many remote hosts. This additional tracking increases implementation complexity and computing resources at the translation device. Because the internal addresses are all disguised behind one publicly accessible address, it is impossible for external hosts to directly initiate a connection to a particular internal host. Applications such as VOIP , videoconferencing , and other peer-to-peer applications must use NAT traversal techniques to function. Pure NAT, operating on IP alone, may or may not correctly parse protocols with payloads containing information about IP, such as ICMP . This depends on whether

806-488: A specific internal address and port. RFC 4787 makes a distinction between NAT mapping and NAT filtering. Section 4.1 of the RFC covers NAT mapping and specifies how an external IP address and port number should be translated into an internal IP address and port number. It defines Endpoint-Independent Mapping, Address-Dependent Mapping and Address and Port-Dependent Mapping, explains that these three possible choices do not relate to

868-530: A web browser is to fetch content and display it on the user's device. This process begins when the user inputs a Uniform Resource Locator (URL), such as https://en.wikipedia.org/ , into the browser. Virtually all URLs on the Web start with either http: or https: which means they are retrieved with the Hypertext Transfer Protocol (HTTP). For secure mode (HTTPS), the connection between

930-465: Is Google Chrome , with a 67% global market share on all devices, followed by Safari with 18%. A web browser is not the same thing as a search engine , though the two are often confused. A search engine is a website that provides links to other websites. However, to connect to a website's server and display its web pages, a user must have a web browser installed. In some technical contexts, browsers are referred to as user agents . The purpose of

992-412: Is PAT or NAT overloading and maps multiple private IP addresses to a single public IP address. Multiple addresses can be mapped to a single address because each private address is tracked by a port number. PAT uses unique source port numbers on the inside global IP address to distinguish between translations. PAT attempts to preserve the original source port. If this source port is already used, PAT assigns

1054-467: Is a stub . You can help Misplaced Pages by expanding it . Network address translation Network address translation ( NAT ) is a method of mapping an IP address space into another by modifying network address information in the IP header of packets while they are in transit across a traffic routing device . The technique was initially used to bypass the need to assign a new address to every host when

1116-514: Is a Cisco proposal that combines Address plus Port translation with tunneling of the IPv4 packets over an ISP provider's internal IPv6 network. In effect, it is an (almost) stateless alternative to carrier-grade NAT and DS-Lite that pushes the IPv4 address /port translation function (and the maintenance of NAT state) entirely into the existing customer premises equipment NAT implementation. Thus avoiding

1178-409: Is a typical configuration: All IP packets have a source IP address and a destination IP address. Typically, packets passing from the private network to the public network will have their source address modified, while packets passing from the public network back to the private network will have their destination address modified. To avoid ambiguity in how replies are translated, further modifications to

1240-520: Is also called port forwarding , or DMZ when used on an entire server , which becomes exposed to the WAN, becoming analogous to an undefended military demilitarized zone (DMZ). The meaning of the term SNAT varies by vendor: Secure network address translation (SNAT) is part of Microsoft's Internet Security and Acceleration Server and is an extension to the NAT driver built into Microsoft Windows Server . It provides connection tracking and filtering for

1302-401: Is an application for accessing websites . When a user requests a web page from a particular website, the browser retrieves its files from a web server and then displays the page on the user's screen. Browsers are used on a range of devices, including desktops , laptops , tablets , and smartphones . By 2020, an estimated 4.9 billion people had used a browser. The most-used browser

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1364-460: Is based on Mozilla 's code. Both of these codebases are open-source, so a number of small niche browsers are also made from them. The most popular browsers share many features in common. They automatically log users' browsing history , unless the users turn off their browsing history or use the non-logging private mode . They also allow users to set bookmarks , customize the browser with extensions , and can manage user passwords . Some provide

1426-478: Is better to refer to specific individual NAT behavior instead of using the Cone/Symmetric terminology. RFC 4787 attempts to alleviate confusion by introducing standardized terminology for observed behaviors. For the first bullet in each row of the above table, the RFC would characterize Full-Cone, Restricted-Cone, and Port-Restricted Cone NATs as having an Endpoint-Independent Mapping , whereas it would characterize

1488-489: Is forwarded to the inside network. Otherwise, if the destination port number of the incoming packet is not found in the translation table, the packet is dropped or rejected because the PAT device doesn't know where to send it. IEEE Reverse Address and Port Translation (RAPT or RAT) allows a host whose real IP address changes from time to time to remain reachable as a server via a fixed home IP address. Cisco 's RAPT implementation

1550-415: Is no need to use a third party (like STUN) to discover the NAT port since the application itself already knows the NAT port. However, if two internal hosts attempt to communicate with the same external host using the same port number, the NAT may attempt to use a different external IP address for the second connection or may need to forgo port preservation and remap the port. As of 2006 , roughly 70% of

1612-436: Is recommended where maximum application transparency is required while Address-Dependent Filtering is recommended where more stringent filtering behavior is most important. Some NAT devices are not yet compliant with RFC 4787 as they treat NAT mapping and filtering in the same way so that their configuration option for changing the NAT filtering method also changes the NAT mapping method (e.g. Netgate TNSR ). The PF firewall has

1674-534: Is that it mitigates IPv4 address exhaustion by allowing entire networks to be connected to the Internet using a single public IP address. Network address and port translation may be implemented in several ways. Some applications that use IP address information may need to determine the external address of a network address translator. This is the address that its communication peers in the external network detect. Furthermore, it may be necessary to examine and categorize

1736-527: The NAT444 and statefulness problems of carrier-grade NAT, and also provides a transition mechanism for the deployment of native IPv6 at the same time with very little added complexity. Hosts behind NAT-enabled routers do not have end-to-end connectivity and cannot participate in some internet protocols. Services that require the initiation of TCP connections from the outside network, or that use stateless protocols such as those using UDP , can be disrupted. Unless

1798-408: The most popular browser. Microsoft debuted Internet Explorer in 1995, leading to a browser war with Netscape. Within a few years, Microsoft gained a dominant position in the browser market for two reasons: it bundled Internet Explorer with its popular Windows operating system and did so as freeware with no restrictions on usage. The market share of Internet Explorer peaked at over 95% in

1860-439: The port preservation design for TCP. For a given outgoing TCP communication, the same port numbers are used on both sides of the NAT. NAT port preservation for outgoing TCP connections is crucial for TCP NAT traversal because, under TCP, one port can only be used for one communication at a time. Programs that bind distinct TCP sockets to ephemeral ports for each TCP communication, make NAT port prediction impossible for TCP. On

1922-507: The NAT router makes a specific effort to support such protocols, incoming packets cannot reach their destination. Some protocols can accommodate one instance of NAT between participating hosts ("passive mode" FTP , for example), sometimes with the assistance of an application-level gateway (see § Applications affected by NAT ), but fail when both systems are separated from the internet by NAT. The use of NAT also complicates tunneling protocols such as IPsec because NAT modifies values in

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1984-420: The NAT. Destination network address translation (DNAT) is a technique for transparently changing the destination IP address of a routed packet and performing the inverse function for any replies. Any router situated between two endpoints can perform this transformation of the packet. DNAT is commonly used to publish a service located in a private network on a publicly accessible IP address. This use of DNAT

2046-434: The RFC include whether they preserve ports, when and how mappings are refreshed, whether external mappings can be used by internal hosts (i.e., its hairpinning behavior), and the level of determinism NATs exhibit when applying all these rules. Specifically, most NATs combine symmetric NAT for outgoing connections with static port mapping , where incoming packets addressed to the external address and port are redirected to

2108-446: The additional network connections needed for the FTP , ICMP , H.323 , and PPTP protocols as well as the ability to configure a transparent HTTP proxy server . Dynamic NAT, just like static NAT, is not common in smaller networks but is found within larger corporations with complex networks. Where static NAT provides a one-to-one internal to public static IP address mapping, dynamic NAT uses

2170-513: The basis for many other browsers, including Microsoft Edge , currently in third place with about a 5% share, as well as Samsung Internet and Opera in fifth and sixth places respectively with over 2% market share each. The other two browsers in the top four are made from different codebases . Safari , based on Apple 's WebKit code, is the second most popular web browser and is dominant on Apple devices, resulting in an 18% global share. Firefox , in fourth place, with about 3% market share,

2232-494: The browser and web server is encrypted , providing a secure and private data transfer. Web pages usually contain hyperlinks to other pages and resources. Each link contains a URL, and when it is clicked or tapped , the browser navigates to the new resource. Most browsers use an internal cache of web page resources to improve loading times for subsequent visits to the same page. The cache can store many items, such as large images, so they do not need to be downloaded from

2294-477: The clients in P2P networks employed some form of NAT. Every TCP and UDP packet contains a source port number and a destination port number. Each of those packets is encapsulated in an IP packet, whose IP header contains a source IP address and a destination IP address. The IP address/protocol/port number triple defines an association with a network socket . For publicly accessible services such as web and mail servers

2356-413: The destination. If the data were sent to port 80 and a DNAT rule exists for port 80 directed to 192.168.1.2 , then the host at that address receives the packet. If no applicable DNAT rule is available, the router drops the packet. An ICMP Destination Unreachable reply may be sent. If any DNAT rules were present, address translation is still in effect; the router still rewrites the source IP address in

2418-646: The early 2000s. In 1998, Netscape launched what would become the Mozilla Foundation to create a new browser using the open-source software model. This work evolved into the Firefox browser, first released by Mozilla in 2004. Firefox's market share peaked at 32% in 2010. Apple released its Safari browser in 2003; it remains the dominant browser on Apple devices, though it did not become popular elsewhere. Google debuted its Chrome browser in 2008, which steadily took market share from Internet Explorer and became

2480-399: The external network. The NAT device then makes an entry in a translation table containing the internal IP address, original source port, and the translated source port. Subsequent packets from the same internal source IP address and port number are translated to the same external source IP address and port number. The computer receiving a packet that has undergone NAT establishes a connection to

2542-421: The first available port number starting from the beginning of the appropriate port group 0–511, 512–1023, or 1024–65535. When there are no more ports available and there is more than one external IP address configured, PAT moves to the next IP address to try to allocate the original source port again. This process continues until it runs out of available ports and external IP addresses. Mapping of Address and Port

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2604-411: The first packet of the fragmented set of packets. Alternatively, the originating host may perform path MTU Discovery to determine the packet size that can be transmitted without fragmentation and then set the don't fragment (DF) bit in the appropriate packet header field. This is only a one-way solution, because the responding host can send packets of any size, which may be fragmented before reaching

2666-631: The first web browser to find mainstream popularity. Its innovative graphical user interface made the World Wide Web easy to navigate and thus more accessible to the average person. This, in turn, sparked the Internet boom of the 1990s, when the Web grew at a very rapid rate. The lead developers of Mosaic then founded the Netscape corporation, which released the Mosaic-influenced Netscape Navigator in 1994. Navigator quickly became

2728-500: The headers which interfere with the integrity checks done by IPsec and other tunneling protocols. End-to-end connectivity has been a core principle of the Internet, supported, for example, by the Internet Architecture Board . Current Internet architectural documents observe that NAT is a violation of the end-to-end principle , but that NAT does have a valid role in careful design. There is considerably more concern with

2790-428: The initial originating transmission is what establishes the required information in the translation tables. Thus a web browser within the private network would be able to browse websites that are outside the network, whereas web browsers outside the network would be unable to browse a website hosted within. Protocols not based on TCP and UDP require other translation techniques. An additional benefit of one-to-many NAT

2852-426: The internet. Ports are endpoints of communication unique to that host, so a connection through the NAT device is maintained by the combined mapping of port and IP address. A private address on the inside of the NAT is mapped to an external public address. Port address translation (PAT) resolves conflicts that arise when multiple hosts happen to use the same source port number to establish different external connections at

2914-408: The main phone number is the public IP address, and the individual extensions are unique port numbers. With NAT, all communications sent to external hosts actually contain the external IP address and port information of the NAT device instead of internal host IP addresses or port numbers. NAT only translates IP addresses and ports of its internal hosts, hiding the true endpoint of an internal host on

2976-508: The most popular browser in 2012. Chrome has remained dominant ever since. By 2015, Microsoft replaced Internet Explorer with Edge for the Windows 10 release. Since the early 2000s, browsers have greatly expanded their HTML , CSS , JavaScript , and multimedia capabilities. One reason has been to enable more sophisticated websites, such as web apps . Another factor is the significant increase of broadband connectivity in many parts of

3038-467: The other hand, for UDP, NATs do not need port preservation. Indeed, multiple UDP communications (each with a distinct endpoint ) can occur on the same source port, and applications usually reuse the same UDP socket to send packets to distinct hosts. This makes port prediction straightforward, as it is the same source port for each packet. Furthermore, port preservation in NAT for TCP allows P2P protocols to offer less complexity and less latency because there

3100-400: The packet. The local computer ( 192.168.1.100 ) sends the packet as coming from 192.168.1.100 , but the server ( 192.168.1.2 ) receives it as coming from 203.0.113.1 . When the server replies, the process is identical to an external sender. Thus, two-way communication is possible between hosts inside the LAN network via the public IP address. Web browser A web browser

3162-478: The packets are required. The vast bulk of Internet traffic uses Transmission Control Protocol (TCP) or User Datagram Protocol (UDP). For these protocols, the port numbers are changed so that the combination of IP address (within the IP header ) and port number (within the Transport Layer header ) on the returned packet can be unambiguously mapped to the corresponding private network destination. RFC 2663 uses

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3224-537: The payload is interpreted by a host on the inside or outside of the translation. Basic protocols as TCP and UDP cannot function properly unless NAT takes action beyond the network layer. IP packets have a checksum in each packet header, which provides error detection only for the header. IP datagrams may become fragmented and it is necessary for a NAT to reassemble these fragments to allow correct recalculation of higher-level checksums and correct tracking of which packets belong to which connection. TCP and UDP, have

3286-402: The port and IP address specified in the altered packet, oblivious to the fact that the supplied address is being translated. Upon receiving a packet from the external network, the NAT device searches the translation table based on the destination port in the packet header. If a match is found, the destination IP address and port number is replaced with the values found in the table and the packet

3348-495: The port number is important. For example, port 443 connects through a socket to the web server software and port 465 to a mail server's SMTP daemon . The IP address of a public server is also important, similar in global uniqueness to a postal address or telephone number. Both IP address and port number must be correctly known by all hosts wishing to successfully communicate. Private IP addresses as described in RFC 1918 are usable only on private networks not directly connected to

3410-406: The same time. A NAT device is similar to a phone system at an office that has one public telephone number and multiple extensions. Outbound phone calls made from the office all appear to come from the same telephone number. However, an incoming call that does not specify an extension cannot be automatically transferred to an individual inside the office. In this scenario, the office is a private LAN,

3472-462: The security of the NAT as security is determined by the filtering behavior and then specifies "A NAT MUST have an 'Endpoint-Independent Mapping' behavior." Section 5 of the RFC covers NAT filtering and describes what criteria are used by the NAT to filter packets originating from specific external endpoints. The options are Endpoint-Independent Filtering, Address-Dependent Filtering and Address and Port-Dependent Filtering. Endpoint-Independent Filtering

3534-401: The server again. Cached items are usually only stored for as long as the web server stipulates in its HTTP response messages. During the course of browsing, cookies received from various websites are stored by the browser. Some of them contain login credentials or site preferences. However, others are used for tracking user behavior over long periods of time, so browsers typically provide

3596-491: The specifics of NAT behavior. IPv4 uses 32-bit addresses, capable of uniquely addressing about 4.3 billion devices. By 1992, it became evident that that would not be enough. The 1994 RFC   1631 describes NAT as a "short-term solution" to the two most compelling problems facing the IP Internet at that time: IP address depletion and scaling in routing. By 2004, NAT had become widespread. The simplest type of NAT provides

3658-414: The term network address and port translation ( NAPT ) for this type of NAT. Other names include port address translation ( PAT ), IP masquerading , NAT overload , and many-to-one NAT . This is the most common type of NAT and has become synonymous with the term NAT in common usage. This method allows communication through the router only when the conversation originates in the private network, since

3720-422: The type of mapping in use, for example when it is desired to set up a direct communication path between two clients both of which are behind separate NAT gateways. For this purpose, RFC 3489 specified a protocol called Simple Traversal of UDP over NATs ( STUN ) in 2003. It classified NAT implementations as full-cone NAT , (address) restricted-cone NAT , port-restricted cone NAT or symmetric NAT , and proposed

3782-411: The use of IPv6 NAT, and many IPv6 architects believe IPv6 was intended to remove the need for NAT. An implementation that only tracks ports can be quickly depleted by internal applications that use multiple simultaneous connections such as an HTTP request for a web page with many embedded objects. This problem can be mitigated by tracking the destination IP address in addition to the port thus sharing

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3844-405: The world, enabling people to access data-intensive content, such as streaming HD video on YouTube , that was not possible during the era of dial-up modems . Google Chrome has been the dominant browser since the mid-2010s and currently has a 67% global market share on all devices. The vast majority of its source code comes from Google's open-source Chromium project; this code is also

#197802