List of IPv6 transition mechanisms
To increase the deployment of IPv6 on the Internet, various transition mechanisms have been proposed to ease this process. Since IPv6 is not directly interoperable with its predecessor protocol IPv4, transition mechanisms 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 conducts working groups and discussions through the IETF Internet Drafts and Request for Comments processes to develop these transition technologies toward that goal. Some basic IPv6 transition mechanisms are defined in RFC 4213.
Stateless IP/ICMP Translation
Stateless IP/ICMP Translation 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 and may be written as, in which the IPv4 formatted address 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.
Tunnel broker
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 or AYIYA.6rd
6rd was developed by Rémi Després. It is a mechanism to facilitate rapid deployment of the IPv6 service across IPv4 infrastructures of Internet service providers. 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.It was used for an early large deployment of an IPv6 service with native addresses during 2007. The standard-track specification of the protocol is in RFC 5969.
Transport Relay Translation
The Transport Relay Translation method acts as an intermediate device between two hosts. The function of the translator is to convert IPV6 into IPV4 addresses and vice versa. TRT accomplishes this translation through IP address mapping and a custom IP address.The address, for example, if packets are to be transmitted from an IPv6 address to an IPv4 address would read as. The packets are routed toward the translator firstly through an IPv6/TCP protocol and then from the translator to the IPv4 host through an IPv4/TCP protocol.
TRT employs a similar operation to DNS translation between AAAA and A records known as DNS ALG.
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.,. 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
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.
- DNS resolver 2606:4700:4700:64 synthesizes AAAA records for
- ipv6test.google.com to a NAT64 address: 64:ff9b::
Non-authoritative answer:
ipv6test.google.com canonical name = ipv6test.l.google.com.
Name: ipv6test.l.google.com
Address: 64:ff9b::8efa:c3e4
;Implementations
ISATAP is an IPv6 transition mechanism meant to transmit IPv6 packets between dual-stack nodes on top of an IPv4 network.
Unlike 6over4, ISATAP uses IPv4 as a virtual nonbroadcast multiple-access network data link layer, so that it does not require the underlying IPv4 network infrastructure to support multicast.
464XLAT
464XLAT allows clients on IPv6-only networks to access IPv4-only Internet services.The client uses a SIIT translator to convert packets from IPv4 to IPv6. These are then sent 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. The NAT64 translator, or PLAT, must be able to reach both the server and the client. The use of NAT64 limits connections to a client–server model using UDP, TCP, and ICMP.
;Implementations
- T-Mobile US became IPv6-only using 464XLAT.
- Orange Polska began IPv6-only service in September 2013, migrating all ADSL, VDSL, and FTTH gateways by January 2015.
- Telstra became IPv6-only for mobile services using 464XLAT in February 2020.
- Android includes a native implementation of CLAT since Jelly Bean 4.3, released in 2013.
- Windows 10 has a native WWAN-only implementation of 464XLAT for desktop and mobile since the 2017 Creators Update.
- Windows 11 is limited to the WWAN interface as in windows 10. Extended CLAT support to other network devices is currently in private preview. The implementation in the preview follows RFC 7050, RFC 8781 standard..
- macOS starts to have native CLAT support in Ventura, released in 2022.
- iOS has a native CLAT implementation since version 12.0, released in 2018. Additionally, Apple requires all apps submitted to the App Store to work on IPv6 networks.
- clatd is a CLAT implementation for Linux.
- Network Manager
- OpenWRT linux OS for routers has optional support for clat via the 464xlat package.
- FreeBSD has implemented NAT64 CLAT since Release 12.1.
Dual-Stack Lite (DS-Lite)
Lightweight 4over6 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.
V4-via-v6 routing
V4-via-v6 routing is a technique where IPv4 addresses are assigned to end hosts only while intermediate routers are only assigned IPv6 addresses. IPv4 routes are propagated as usual, and no packet translation or encapsulation is employed, but use an IPv6 next hop. V4-via-v6 reduces the amount of management required, since the core network only needs to be assigned IPv6 addresses, but still requires that the core network be able to forward IPv4 packets.V4-via-v6 is defined for the Border Gateway Protocol and the Babel routing protocol. It has been implemented in the Bird Internet routing daemon and in babeld.