Understanding Interface Identifiers

For all the types of unicast IPv6 addresses described in the preceding sections, the last 64 bits of the address represent the interface ID and are used to specify a unique interface on a local link or subnet. In previous versions of Windows, the interface ID is uniquely determined as follows:

• For link-local addresses, such as a network adapter on an Ethernet segment, the interface ID is derived from either the unique 48-bit media access control (MAC)-layer address of the interface or the unique Extended Unique Identifier (EUI)-64 address of the interface as defined by the Institute of Electrical and Electronics Engineers (IEEE).
• For global address prefixes, an EIU-64-based interface ID creates a public IPv6 address.
• For global address prefixes, a temporary random interface ID creates a temporary address. This approach is described in RFC 3041; you can use it to help provide anonymity for client-based usage of the IPv6 Internet.

In Windows 7, however, the interface ID by default is randomly generated for all types of unicast IPv6 addresses assigned to LAN interfaces.

Note Windows 7 randomly generates the interface ID by default. You can also disable this behavior by typing netsh interface ipv6 set global randomizedidentifiers=disabled at a command prompt.