This article is based on a prerelease version of Windows Server 2008. All information herein is subject to change.
A common misperception about Internet Protocol version 6 (IPv6) is that in order to use it, you must deploy native IPv6 addressing and routing, which requires a detailed analysis of IPv6 addressing schemes, router updates and configuration, and a rollout schedule. Although this should eventually be done for native
IPv6 connectivity, you can easily deploy tunneled IPv6 connectivity using the Intra-Site Automatic Tunnel Addressing Protocol (ISATAP). With tunneled IPv6 connectivity, hosts that support ISATAP can communicate using IPv6 traffic that is encapsulated with an IPv4 header (the IPv4 Protocol field is set to 41). ISATAP traffic can traverse an IPv4-only intranet, so you can begin testing IPv6-capable applications immediately, without having to wait for a native IPv6 infrastructure.
ISATAP is an address assignment and automatic tunneling technology defined in RFC 4214 that provides unicast IPv6 connectivity between IPv6/IPv4 hosts across an IPv4- only intranet. ISATAP hosts use a logical tunneling interface that is assigned ISATAP addresses, which have the form UnicastPrefix:0:5EFE:w.x.y.z (when w.x.y.z is a private IPv4 address assigned to the ISATAP host) or UnicastPrefix:200:5EFE:w.x.y.z (when w.x. y.z is a public IPv4 address assigned to the ISATAP host). UnicastPrefix is any 64-bit unicast address prefix, including link-local, global, and unique local prefixes. Examples of ISATAP addresses are 2001:DB8::98CA:200:188.8.131.52 and 2001:DB8::98CA:0:10.91.211.17.
Intranet Migration to IPv6 with ISATAP: An ISATAP deployment consists of one or more logical ISATAP subnets, which are IPv4-only networks assigned a 64-bit IPv6 subnet prefix. On a logical ISATAP subnet there are ISATAP hosts and ISATAP routers. An ISATAP host uses an ISATAP tunneling interface to encapsulate IPv6 traffic. This traffic can be sent directly to other ISATAP hosts on the same logical ISATAP subnet. To reach destinations that are on other ISATAP subnets or on native IPv6 subnets, the traffic is sent to an ISATAP router. An ISATAP router is an IPv6 router that advertises subnet prefixes to ISATAP hosts and forwards IPv6 traffic between ISATAP hosts and hosts on other IPv6 subnets. Figure 1 shows the components of ISATAP on a simplified intranet.
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