Tuesday, July 19, 2011

The ISATAP Tunneling Protocol

The Intra-Site Automatic Tunnel Addressing Protocol (ISATAP) is an IPv6 transition protocol. It provides for the automatic conversion of an IPv4 address to an IPv6 address, as well as a mechanism for setting up a virtual IPv6 network that transmits over an IPv4 network. The protocol does not require any manual configuration.

The components of ISATAP are the following:

» ISATAP host—The ISATAP host communicates IPv6 over IPv4 networks with other ISATAP hosts and with ISATAP routers.

» ISATAP router—The ISATAP router advertises address prefixes to the local ISATAP subnet, forwards ISATAP traffic to IPv6 networks, and acts as the default route for ISATAP hosts.

Link-local addresses are network addresses that are only designed to communicate on a segment and basically allow communications with neighboring devices without needing a globally routable address. They are mandatory in IPv6 and are automatically assigned with the FE80::/10 prefix.

This is useful for deploying IPv6 without having to explicitly define and configure a IPv6 network addressing scheme because it allows IPv6 devices to communicate over IPv4 networks.

The Windows Vista RTM, Windows Server 2003, and Windows XP all automatically enable and configure the ISATAP tunneling adapter if the IPv6 protocol is installed. These operating systems use the name Automatic Tunneling Pseudo-Interface rather than ISATAP to identify the adapter.

The Windows Server 2008 R2, Windows 2008, Windows 7, and Windows Vista SP1 operating systems do not enable the ISATAP tunneling adapter unless they can resolve the name “ISATAP” in to an IPv4 address. The ISATAP address is the IPv4 address of the local ISATAP router. The name resolution can use any of the standard methods to resolve, including DNS, WINS, NetBIOS broadcast, or the LMHOSTS file. When these operating systems are able to resolve the ISATAP address, they configure the ISATAP tunneling adapter and add a default route of ::/0 to the link-local address of the ISATAP router.

ISATAP address IPv4 to IPv6 address translation is done by concatenating a 64-bit prefix with :0000:5EFE:w.x.y.z, where w.x.y.z is the IPv4 address in dotted decimal format. The prefix can be a link-local prefix (that is, FE80::/64), a global prefix (for example, FC00:1234:5678:9abc::/64), or even a global 6to4 prefix (for example, 2002:c9b:a602:1:0::/64), discussed in the next section. Table 10.3 lists some example values for IP address conversions in ISATAP.

The format FE80::5EFE:w.x.y.z is functionally equivalent to the format FE80::5EFE:WWXX:YYZZ, where the dotted decimal IPv4 address format is converted to hexadecimal format. Each decimal number (for example, w) is converted to a two-digit hexadecimal number (for example, WW). In the first example above, the IPv6 address FE80::5EFE: would be expressed as FE80::5EFE:0C9B:A665. This format is known as the colon hexadecimal format.

Source of Information : Sams - Windows Server 2008 R2 Unleashed (2010)

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