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12. Identity Association

This section preserves the RFC text for DHCPv6, including message exchanges, relay behavior, DUIDs, IA_NA, IA_TA, IA_PD, DHCP options, RKAP authentication, IANA registries, normative requirements, and appendix option-appearance matrices.

Original RFC Text​

12.  Identity Association

   An Identity Association (IA) is a construct through which a server
   and a client can identify, group, and manage a set of related IPv6
   addresses or delegated prefixes.  Each IA consists of an IAID and
   associated configuration information.

   The IAID uniquely identifies the IA and MUST be chosen to be unique
   among the IAIDs for that IA type on the client (e.g., an IA_NA with
   an IAID of 0 and an IA_PD with an IAID of 0 are each considered
   unique).  The IAID is chosen by the client.  For any given use of an
   IA by the client, the IAID for that IA MUST be consistent across
   restarts of the DHCP client.  The client may maintain consistency by
   either storing the IAID in non-volatile storage or using an algorithm
   that will consistently produce the same IAID as long as the
   configuration of the client has not changed.  There may be no way for
   a client to maintain consistency of the IAIDs if it does not have
   non-volatile storage and the client's hardware configuration changes.
   If the client uses only one IAID, it can use a well-known value,
   e.g., zero.

   If the client wishes to obtain a distinctly new address or prefix and
   deprecate the existing one, the client sends a Release message to the
   server for the IAs using the original IAID.  The client then creates
   a new IAID, to be used in future messages to obtain leases for the
   new IA.

12.1.  Identity Associations for Address Assignment

   A client must associate at least one distinct IA with each of its
   network interfaces for which it is to request the assignment of IPv6
   addresses from a DHCP server.  The client uses the IAs assigned to an
   interface to obtain configuration information from a server for that
   interface.  Each such IA must be associated with exactly one
   interface.

   The configuration information in an IA_NA option consists of one or
   more IPv6 addresses along with the T1 and T2 values for the IA.  See
   Section 21.4 for details regarding the representation of an IA_NA in
   a DHCP message.

   Each address in an IA has a preferred lifetime and a valid lifetime,
   as defined in [RFC4862].  The lifetimes are transmitted from the DHCP
   server to the client in the IA Address option (see Section 21.6).
   The lifetimes apply to the use of addresses; see Section 5.5.4 of
   [RFC4862].

12.2.  Identity Associations for Prefix Delegation

   An IA_PD is different from an IA for address assignment in that it
   does not need to be associated with exactly one interface.  One IA_PD
   can be associated with the client, with a set of interfaces, or with
   exactly one interface.  A client configured to request delegated
   prefixes must create at least one distinct IA_PD.  It may associate a
   distinct IA_PD with each of its downstream network interfaces and use
   that IA_PD to obtain a prefix for that interface from the server.

   The configuration information in an IA_PD option consists of one or
   more prefixes along with the T1 and T2 values for the IA_PD.  See
   Section 21.21 for details regarding the representation of an IA_PD in
   a DHCP message.

   Each delegated prefix in an IA has a preferred lifetime and a valid
   lifetime, as defined in [RFC4862].  The lifetimes are transmitted
   from the DHCP server to the client in the IA Prefix option (see
   Section 21.22).  The lifetimes apply to the use of delegated
   prefixes; see Section 5.5.4 of [RFC4862].
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