Coexistence Mechanisms

To coexist with an IPv4 infrastructure and to provide eventual migration to an IPv6-only infrastructure, the following mechanisms are used:

• Dual IP layer
• IPv6 over IPv4 tunneling
• DNS infrastructure

Dual IP Layer: The dual IP layer is an implementation of the TCP/IP suite of protocols that includes both an IPv4 Internet layer and an IPv6 Internet layer. This is the mechanism used by IPv6/IPv4 nodes so that communication with both IPv4 and IPv6 nodes can occur. A dual IP layer contains a single implementation of Host-to-Host layer protocols such as TCP and UDP. All upper layer protocols in a dual IP layer implementation can communicate over IPv4, IPv6, or IPv6 tunneled over IPv4.

The dual IP layer architecture The dual stack architecture

The IPv6 protocol for Windows XP and the Windows 2003 family is not a dual IP layer. The IPv6 protocol driver, Tcpip6.sys, contains a separate implementation of TCP and UDP and is sometimes referred to as a dual-stack implementation.