IPv6 transition mechanism

[1] The Internet Engineering Task Force (IETF) conducts working groups and discussions through the IETF Internet Drafts and Request for Comments processes to develop these transition technologies towards that goal.

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.

[4] A tunnel broker provides IPv6 connectivity by encapsulating IPv6 traffic in IPv4 Internet transit links, typically using 6in4.

[12] TRT employs a similar operation to DNS translation between AAAA and A records known as DNS-ALG as defined in RFC 2694.

[15] There are two noticeable issues with this transition mechanism: 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.

464XLAT (RFC 6877) allows clients on IPv6-only networks to access IPv4-only Internet services.

Dual-Stack Lite technology does not involve allocating an IPv4 address to customer-premises equipment (CPE) for providing Internet access.

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.

IPv4 routes are propagated as usual, and no packet translation or encapsulation is employed, but use an IPv6 next hop.

[37] 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.

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.