IPv6 transition mechanism
An IPv6 transition mechanism is a technology that facilitates the transitioning of the Internet from the Internet Protocol version 4 (IPv4) infrastructure in use since 1983 to the successor addressing and routing system of Internet Protocol Version 6 (IPv6). As IPv4 and IPv6 networks are not directly interoperable, transition technologies are designed to permit hosts on either network type to communicate with any other host.
To meet its technical criteria, IPv6 must have a straightforward transition plan from the current IPv4. The Internet Engineering Task Force (IETF) conducts working groups and discussions through the IETF Internet Drafts and Requests for Comments processes to develop these transition technologies towards that goal. Some basic IPv6 transition mechanisms are defined in RFC 4213.
Stateless IP/ICMP TranslationEdit
Stateless IP/ICMP Translation (SIIT) translates between the packet header formats in IPv6 and IPv4. The SIIT method defines a class of IPv6 addresses called IPv4-translated addresses. They have the prefix ::ffff:0:0:0/96 and may be written as ::ffff:0:a.b.c.d, in which the IPv4 formatted address a.b.c.d refers to an IPv6-enabled node. The prefix was chosen to yield a zero-valued checksum to avoid changes to the transport protocol header checksum. The algorithm can be used in a solution that allows IPv6 hosts that do not have a permanently assigned IPv4 address to communicate with IPv4-only hosts. Address assignment and routing details are not addressed by the specification. SIIT can be viewed as a special case of stateless network address translation.
The specification is a product of the NGTRANS IETF working group, and was initially drafted in February 2000 by E. Nordmark of Sun Microsystems. It was revised in 2011, and in 2016 its current revision was published.
A tunnel broker provides IPv6 connectivity by encapsulating IPv6 traffic in IPv4 Internet transit links, typically using 6in4. This establishes IPv6 tunnels within the IPv4 Internet. The tunnels may be managed with the Tunnel Setup Protocol (TSP) or AYIYA.
6rd is a mechanism to facilitate rapid deployment of the IPv6 service across IPv4 infrastructures of Internet service providers (ISPs). It uses stateless address mappings between IPv4 and IPv6 addresses, and transmits IPv6 packets across automatic tunnels that follow the same optimized routes between customer nodes as IPv4 packets.
Transport Relay TranslationEdit
RFC 3142 defines the Transport Relay Translation (TRT) method. TRT employs DNS translation between AAAA and A records known as DNS-ALG as defined in RFC 2694.
NAT64 is a mechanism to allow IPv6 hosts to communicate with IPv4 servers. The NAT64 server is the endpoint for at least one IPv4 address and an IPv6 network segment of 32-bits, e.g., 64:ff9b::/96 (RFC 6052, RFC 6146). The IPv6 client embeds the IPv4 address with which it wishes to communicate using these bits, and sends its packets to the resulting address. The NAT64 server then creates a NAT-mapping between the IPv6 and the IPv4 address, allowing them to communicate.
DNS64 describes a DNS server that when asked for a domain's AAAA records, but only finds A records, synthesizes the AAAA records from the A records. The first part of the synthesized IPv6 address points to an IPv6/IPv4 translator and the second part embeds the IPv4 address from the A record. The translator in question is usually a NAT64 server. The standard-track specification of DNS64 is in RFC 6147.
There are two noticeable issues with this transition mechanism:
- It only works for cases where DNS is used to find the remote host address, if IPv4 literals are used the DNS64 server will never be involved.
- Because the DNS64 server needs to return records not specified by the domain owner, DNSSEC validation against the root will fail in cases where the DNS server doing the translation is not the domain owner's server.
ISATAP (Intra-Site Automatic Tunnel Addressing Protocol) is an IPv6 transition mechanism meant to transmit IPv6 packets between dual-stack nodes on top of an IPv4 network.
Unlike 6over4 (an older similar protocol using IPv4 multicast), ISATAP uses IPv4 as a virtual nonbroadcast multiple-access network (NBMA) data link layer, so that it does not require the underlying IPv4 network infrastructure to support multicast.
The client uses a SIIT translator to convert packets from IPv4 to IPv6. These are then send to a NAT64 translator which translates them from IPv6 back into IPv4 and on to an IPv4-only server. The client translator may be implemented on the client itself or on an intermediate device and is known as the CLAT (Customer-side transLATor). The NAT64 translator, or PLAT (Provider-side transLATor), must be able to reach both the server and the client (through the CLAT). The use of NAT64 limits connections to a client-server model using UDP, TCP, and ICMP.
- There is a CLAT implementation for Android, Android CLAT. T-Mobile USA provides NAT64 with T-Mobile's IPv6-only service.[unreliable source?]
- Orange Poland began IPv6-only (CLAT/NAT64/DNS) service in September 2013.
- Android native CLAT implementation appeared in Jelly Bean 4.3.
- Windows Phone introduced a native CLAT implementation in 2014 with WP 8.1.
- Windows 10 (Creators update) has a native 464XLAT implementation for desktop and mobile. It is enabled for WWAN interfaces when the Mobile Operator has enabled 464xlat on the network 
- iOS 12.0 features a native CLAT implementation. Additionally, Apple requires all apps submitted to the App Store to work on IPv6 networks.
- clatd is a CLAT implementation for Linux.
- FreeBSD has had CLAT implementations since 11.3 and 12.1.
Dual-Stack Lite (DS-Lite)Edit
Dual-Stack Lite technology does not involve allocating an IPv4 address to customer-premises equipment (CPE) for providing Internet access. It is described in RFC 6333. The CPE distributes private IPv4 addresses for the LAN clients, according to the networking requirement in the local area network. The CPE encapsulates IPv4 packets within IPv6 packets. The CPE uses its global IPv6 connection to deliver the packet to the ISP's carrier-grade NAT (CGN), which has a global IPv4 address. The original IPv4 packet is recovered and NAT is performed upon the IPv4 packet and is routed to the public IPv4 Internet. The CGN uniquely identifies traffic flows by recording the CPE public IPv6 address, the private IPv4 address, and TCP or UDP port number as a session.
Lightweight 4over6 (RFC 7596) extends DS-Lite by moving the NAT functionality from the ISP side to the CPE, eliminating the need to implement carrier-grade NAT. This is accomplished by allocating a port range for a shared IPv4 address to each CPE. Moving the NAT functionality to the CPE allows the ISP to reduce the amount of state tracked for each subscriber, which improves the scalability of the translation infrastructure.
These mechanisms are still being discussed or have been abandoned by the IETF.
IPv4 Residual Deployment (4rd) is a mechanism specified in RFC 7600 to facilitate residual deployment of the IPv4 service across IPv6 networks. Like 6rd, it uses stateless address mappings between IPv6 and IPv4. It supports an extension of IPv4 addressing based on transport-layer ports. This is a stateless variant of the A+P model.
Mapping of Address and Port (MAP) is a Cisco IPv6 transition proposal which combines A+P port address translation with tunneling of the IPv4 packets over an ISP provider's internal IPv6 network. As of July 2015[update], MAP-T and MAP-E are proposed standards.
These mechanisms have been deprecated by the IETF.
Network Address Translation/Protocol Translation (NAT-PT) is defined in RFC 2766, but due to numerous problems, it has been obsoleted by RFC 4966 and deprecated to historic status. It is typically used in conjunction with a DNS application-level gateway (DNS-ALG) implementation.
While almost identical to NAT-PT, Network Address Port Translation + Protocol Translation, which is also described in RFC 2766, adds translation of the ports as well as the address. This is done primarily to avoid two hosts on one side of the mechanism from using the same exposed port on the other side of the mechanism, which could cause application instability and/or security flaws. This mechanism has been deprecated by RFC 4966.
- stone (software), port translator for Windows & Unix-based systems.
- faithd, BSD-based static TRT implementation by the KAME project
- CLATD, a CLAT / SIIT-DC Edge Relay implementation for Linux
- WrapSix, a NAT64 implementation for Linux
- TAYGA, a stateless NAT64 implementation for Linux
- Jool, a stateful NAT64 implementation for Linux
- naptd, user-level NAT-PT
- Ecdysis, a NAT64 gateway, includes DNS64
- Address Family Transition Router (AFTR), a DS-Lite implementation
- niit Linux Kernel device that allow transmission of IPv4 unicast traffic through an IPv6 network
- IVI IPv4/IPv6 packet translation implementation as a Linux kernel(2.6 only) patch
- Microsoft Forefront Unified Access Gateway, a reverse proxy and VPN solution that implements DNS64 and NAT64
- BIND, Berkeley Internet Name Domain DNS server, implements DNS64 since version 9.8
- PF (firewall), the OpenBSD packet filter supports IP version translation since version 5.1, includes NAT64
- IPv6 in Practice, Benedikt Stockebrand (2006), ISBN 3-540-24524-3
- RFC 2767, Bump-in-the-Stack
- RFC 3338, Bump-in-the-API
- RFC 3089, Socks-based Gateway
- RFC 6219, The China Education and Research Network (CERNET) IVI Translation Design and Deployment for the IPv4/IPv6 Coexistence and Transition
- RFC 1726 - IPng Technical Criteria
- F. Baker; X. Li; C. Bao; K. Yin (April 2011). Framework for IPv4/IPv6 Translation. IETF. doi:10.17487/RFC6144. RFC 6144.
- C. Bao; C. Huitema; M. Bagnulo; M. Boucadair; X. Li (October 2010). IPv6 Addressing of IPv4/IPv6 Translators. IETF. doi:10.17487/RFC6052. RFC 6052.
- C. Bao; X. Li; F. Baker; T. Anderson; F. Gont (June 2016). Stateless IP/ICMP Translation Algorithm. doi:10.17487/RFC7915. RFC 7915.
- E. Nordmark (February 2000). Stateless IP/ICMP Translation Algorithm (SIIT). Network Working Group. doi:10.17487/RFC2765. RFC 2765.
- X. Li; C. Bao; F. Baker (April 2011). IP/ICMP Translation Algorithm. IETF. doi:10.17487/RFC6145. RFC 6145.
- RFC 5569 IPv6 Rapid Deployment on IPv4 Infrastructures (6rd)
- RFC 5969 IPv6 Rapid Deployment on IPv4 Infrastructures (6rd) -- Protocol Specification
- RFC 6146 Stateful NAT64: Network Address and Protocol Translation from IPv6 Clients to IPv4 Servers
- RFC 6147 DNS64: DNS Extensions for Network Address Translation from IPv6 Clients to IPv4 Servers
- "Video: 464XLAT Live Demo at World IPv6 Congress in Paris". Internet Society. 3 April 2013.
- "464XLAT -- A Solution for Providing IPv4 Services Over and IPv6-only Network". T-Mobile USA. Retrieved 5 August 2013.
- "T-Mobile IPv6 is Here and Now". T-Mobile USA. Retrieved 5 August 2013.
- Orange Polska#Mobile network
- "Windows Phone Hardware Development".
- "Core Network Stack Features in the Creators Update for Windows 10". Retrieved 26 July 2017.
- "Win10 update CLAT". Retrieved 9 August 2017.
- "[v6ops] iOS12 IPv6-only". Retrieved 5 November 2018.
- van Beijnum, Iljitsch (2015-06-16). "Apple to iOS devs: IPv6-only cell service is coming soon, get your apps ready". Ars Technica. Retrieved 2 July 2016.
- "D19561 NAT64 update". FreeBSD phabricator.
- RFC 6333 - Dual-Stack Lite Broadband Deployments Following IPv4 Exhaustion
- Cui, Y.; Sun, Q.; Tsou, T.; Lee, Y.; Farrer, I. (July 2015). Lightweight 4over6: An Extension to the Dual-Stack Lite Architecture. IETF. doi:10.17487/RFC7596. RFC 7596. Retrieved 2018-05-25.
- Mark Townsley (September 24, 2012). "Mapping Address + Port" (PDF). Cisco. Retrieved 2012-09-25.
- Congxiao, Bao; Wojciech, Dec; Xing, Li; Ole, Troan; Satoru, Matsushima; Tetsuya, Murakami. "Mapping of Address and Port using Translation (MAP-T)". tools.ietf.org. Retrieved 2018-06-07.
- Congxiao, Bao; Tom, Taylor; Wojciech, Dec; Xing, Li; Ole, Troan; Satoru, Matsushima; Tetsuya, Murakami. "Mapping of Address and Port with Encapsulation (MAP-E)". tools.ietf.org. Retrieved 2018-06-07.
- D. J. Bernstein - The IPv6 mess
- TRT Howto from 2013
- IPv6 - Prospects and problems: a technical and management investigation into the deployment of IPv6
- Network World: Understanding Dual-Stack Lite
- IETF Draft: Framework for IPv4/IPv6 Translation
- IPv4 and IPv6 Transition and Coexistence, 6DEPLOY project, 2011
- Assuring Interoperability Between Heterogeneous (IPv4/IPv6 Networks Without using Protocol Translation, IETE Technical Review, 2012
- Configuring Hosts to Auto-detect (IPv6, IPv6-in-IPv4, or IPv4) Network Connectivity, KSII TRANSACTIONS ON INTERNET AND INFORMATION SYSTEMS, 2011
- IPv6: NAT-PT versus NAT64 Gianrico Fichera, 2012