Configure TCP/IP - MCSA Windows Server 2012 R2: Installation and Configuration Study Guide - page 429

IPv6 Dual Stack
The default implementation in Windows Server 2012 R2 is an enabled IPv6 configuration
along with IPv4; this is dual stack. The implementation can be dual IP layer or dual TCP/
IP stack. Windows Server 2012 R2 uses the dual IP layer implementation (see Figure 8.16).
When an application queries a DNS server to resolve a hostname to an IP address, the DNS
server may respond with an IPv4 address or an IPv6 address. If the DNS server responds
with both, Windows Server 2012 R2 will prefer the IPv6 address. Windows Server 2012
R2 can use both IPv4 and IPv6 addresses as necessary for network communication. When
looking at the output of the ipconfig command, you will see both address spaces displayed.

fIgure 8.16 IPv6 dual IP layer diagram

Application Layer

Transport Layer

Network Layer

Application
IPv4 IPv6

Network Interface

IPv6 Tunneling
Windows Server 2012 R2 includes several tunneling mechanisms for tunneling IPv6
through the IPv4 address space. They include the following:
■ Intra-Site Automatic Tunnel Addressing Protocol (ISATAP), which is used for unicast
IPv6 communication across an IPv4 infrastructure. ISATAP is enabled by default in
Windows Server 2012 R2.
■ 6to4, which is used for unicast IPv6 communication across an IPv4 infrastructure.
■ Teredo, which is used for unicast IPv6 communication with an IPv4 NAT implementa-
tion across an IPv4 infrastructure.
With multiple tunneling protocols available and enabled by default, you might ask, what's
the difference, and why is one used over the others? They all allow you to tunnel IPv6 packets
through the IPv4 address space (a really cool thing if you're trying to integrate/migrate). Here
are the details of these tunneling mechanisms:
ISATAP Intra-Site Automatic Tunnel Addressing Protocol (ISATAP) is the automatic
tunnel addressing protocol providing IPv6 addresses based on the IPv4 address of the end
interface (node). The IPv6 address is automatically configured on the local device, and the