Interface Tokens, Link Layer Address Options, Link-Local Addresses

Interface Tokens

    Each IPv6 interface must have an interface token from which to form IPv6 autoconfigured

    addresses.This interface token must be unique within a Logical Link to prevent the creation of

    duplicate addresses when stateless address configuration is used.

    In cases where two nodes on the same LL produce the same interface token then one interface MUST

    choose another host-token. All implementations must allow operators to manually change a interface

    token on a per-LL basis.

    All interface tokens must be 64 bits in length and formatted as described in the following sections.

Single Logical Links on a Single NBMA Interface

     Physical NBMA interfaces will generally have some local identifier that may be used to generate a

     unique IPv6/NBMA interface token.

Multiple Logical Links on a Single NBMA Interface

    Physical NBMA interfaces may be used to provide multiple logical NBMA interfaces. Since each

    logical NBMA interface may support an independent IPv6 interface, two separate scenarios are

    possible:

    A single host with separate IPv6/NBMA interfaces onto a number of independent Logical Links.

    each interface's external identity can be differentiated by the LL's routing prefix .

    meaning host can re-use a single unique interface token across all itsIPv6/NBMAinterfaces.

    A set of 2 or more 'virtual hosts' (vhosts) sharing a common NBMA driver.

    Each host is free to establish IPv6/NBMA interfaces.

Link Layer Address Options

    Neighbor Discovery defines two option fields for carrying link-layer specific source and target

    addresses. The format for these two options is adapted from the MARS and NHRP specs is :

            [Type][Length][NTL][STL][..NBMA Number..][..NBMA

            Subaddress..]| Fixed ||Link layer address|

    [Type] is a one octet field.

        1 for Source link-layer address.

        2 for Target link-layer address.

    [Length] is a one octet field.

    The total length of the option in multiples of 8 octets. Zeroed bytes are added to the end of the option

    to ensure its length is a multiple of 8 octets.

    [NTL] is a one octet 'Number Type & Length' field.

    [STL] is a one octet 'SubAddress Type & Length' field.

    [NBMA Number] is a variable length field. It is always present.

    This contains the primary NBMA address.  

    [NBMA Subaddress] is a variable length field. It may or may not be present.

    This contains any NBMA subaddress that may be required.

    If the [NBMA Subaddress] is not present, the option ends after the [NBMA Number]

    (and any additional padding for 8 byte alignment). 

Link-Local Addresses

    The IPv6 link-local address is formed by appending the interface token, as defined above,

    to the prefix FE80::/64.