Intra-Site Automatic Tunnel Addressing Protocol (ISATAP) connects dual-stack (IPv6/IPv4) nodes over IPv4 networks. ISATAP views the IPv4 network as a link layer for IPv6 and supports an automatic tunneling abstraction similar to the Non-Broadcast Multiple Access (NBMA) model.

Each ISATAP interface configures a set of locators consisting of IPv4 address-to-interface mappings from a single site; i.e., an ISATAP interface's locator set MUST NOT span multiple sites.

When an IPv4 address is removed from an interface, the corresponding locator SHOULD be removed from its associated locator set(s). When a new IPv4 address is assigned to an interface, the corresponding locator MAY be added to the appropriate locator set(s). ISATAP interfaces form ISATAP interface identifiers from IPv4 addresses in their locator set and use them to create link-localISATAP addresses.

ISATAP addresses are mapped to a link-layer address by a static computation; i.e., the last four octets are treated as an IPv4 address.

When an ISATAP node receives an IPv4 protocol 41 datagram that does not belong to a configured tunnel interface, it determines whether the packet's IPv4 destination address and arrival interface match a locator configured in an ISATAP interface's locator set.

If an ISATAP interface that configures a matching locator is found, the decapsulator MUST verify that the packet's IPv4 source address is correct for the encapsulated IPv6 source address.

Protocol Structure

ISATAP interface identifiers are constructed in Modified EUI-64 format by concatenating the 24-bit IANA OUI (00-00-5E), the 8-bit hexadecimal value 0xFE, and a 32-bit IPv4 address in network byte order as follows:

When the IPv4 address is known to be globally unique, the "u" bit

(universal/local) is set to 1; otherwise, the "u" bit is set to 0.

"g" is the individual/group bit, and "m" represents the bits of the

IPv4 address. ISATAP nodes are not required to validate that interface identifiers created with modified EUI-64 tokens with the "u" bit set to universal are unique.

Related Protocols: IPv4, IPv6

Sponsor Source: ISATAP is defined by IETF http://www.ietf.org

Reference: http://www.javvin.com/protocol/rfc5214.pdf: Intra-Site Automatic Tunnel Addressing Protocol (ISATAP)