DHC Working Group                                               O. TroanInternet-Draft                                                  R. DromsExpires: September 1, 2003                                 Cisco Systems                                                           March 3, 2003                     IPv6 Prefix Options for DHCPv6           draft-ietf-dhc-dhcpv6-opt-prefix-delegation-03.txtStatus of this Memo   This document is an Internet-Draft and is in full conformance with   all provisions of Section 10 of RFC2026.   Internet-Drafts are working documents of the Internet Engineering   Task Force (IETF), its areas, and its working groups.  Note that   other groups may also distribute working documents as Internet-   Drafts.   Internet-Drafts are draft documents valid for a maximum of six months   and may be updated, replaced, or obsoleted by other documents at any   time.  It is inappropriate to use Internet-Drafts as reference   material or to cite them other than as "work in progress."   The list of current Internet-Drafts can be accessed at http://   www.ietf.org/ietf/1id-abstracts.txt.   The list of Internet-Draft Shadow Directories can be accessed at   http://www.ietf.org/shadow.html.   This Internet-Draft will expire on September 1, 2003.Copyright Notice   Copyright (C) The Internet Society (2003).  All Rights Reserved.Abstract   The Prefix Delegation options provide a mechanism for automated   delegation of IPv6 prefixes using DHCP.  This mechanism is intended   for delegating long-lived prefix from a delegating router to a   requesting router, across an administrative boundary, where the   delegating router does not require knowledge about the topology of   the links in the network to which the prefixes will be assigned.Troan & Droms          Expires September 1, 2003                [Page 1]Internet-Draft       IPv6 Prefix Options for DHCPv6           March 2003Table of Contents   1.   Introduction . . . . . . . . . . . . . . . . . . . . . . . .   3   2.   DHCPv6 specification dependency  . . . . . . . . . . . . . .   3   3.   Terminology  . . . . . . . . . . . . . . . . . . . . . . . .   3   4.   Requirements . . . . . . . . . . . . . . . . . . . . . . . .   4   5.   Model and Applicability  . . . . . . . . . . . . . . . . . .   4   5.1  Example network architecture . . . . . . . . . . . . . . . .   4   6.   Identity Association for Prefix Delegation . . . . . . . . .   6   7.   Overview of DHCP with Prefix Delegation  . . . . . . . . . .   7   8.   Interface Selection  . . . . . . . . . . . . . . . . . . . .   7   9.   Identity Association for Prefix Delegation Option  . . . . .   8   10.  IA_PD Prefix option  . . . . . . . . . . . . . . . . . . . .  10   11.  Delegating Router Solicitation . . . . . . . . . . . . . . .  11   11.1 Requesting router behaviour  . . . . . . . . . . . . . . . .  11   11.2 Delegating router behaviour  . . . . . . . . . . . . . . . .  12   12.  Requesting router initiated prefix delegation  . . . . . . .  13   12.1 Requesting router behaviour  . . . . . . . . . . . . . . . .  13   12.2 Delegating Router behaviour  . . . . . . . . . . . . . . . .  14   13.  Prefix Delegation reconfiguration  . . . . . . . . . . . . .  16   13.1 Delegating Router behaviour  . . . . . . . . . . . . . . . .  16   13.2 Requesting Router behaviour  . . . . . . . . . . . . . . . .  16   14.  Relay agent behaviour  . . . . . . . . . . . . . . . . . . .  16   15.  Security Considerations  . . . . . . . . . . . . . . . . . .  16   16.  IANA Considerations  . . . . . . . . . . . . . . . . . . . .  17   17.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . .  17   18.  Changes in draft-ietf-dhc-dhcpv6-opt-prefix-delegation-03  .  17        Normative References . . . . . . . . . . . . . . . . . . . .  18        Informative References . . . . . . . . . . . . . . . . . . .  18        Authors' Addresses . . . . . . . . . . . . . . . . . . . . .  18        Full Copyright Statement . . . . . . . . . . . . . . . . . .  20Troan & Droms          Expires September 1, 2003                [Page 2]Internet-Draft       IPv6 Prefix Options for DHCPv6           March 20031. Introduction   This document describes new options for DHCP, which provide a   mechanism for the delegation of IPv6 prefixes.  Through these   options, a delegating router can delegate prefixes to authorised   requesting routers.   The prefix delegation mechanism described in this document is   intended for simple delegation of prefixes from a delegating router   to requesting routers.  It is appropriate for situations in which the   delegating router does not have knowledge about the topology of the   networks to which the requesting router is attached, and the   delegating router does not require other information aside from the   identity of the requesting router to choose a prefix for delegation.   For example, these options would be used by a service provider to   assign a prefix to a CPE device acting as a router between the   subscriber's internal network and the service provider's core   network.   Many applications expect stable addresses.  Even though this   mechanism makes automatic renumbering easier, it is expected that   prefixes have a long lifespan.  During renumbering it is expected   that the old and the new prefix co-exist for some time.   The design of this prefix delegation mechanism meets the requirements   for prefix delegation in Requirements for IPv6 prefix delegation [8].2. DHCPv6 specification dependency   This document describes an extension to the DHCPv6 specification [6].   This document should be read in conjunction with the DHCPv6   specification for a complete specification of the Prefix Delegation   options and mechanism.  Definitions for terms and acronyms not   specifically defined in this document are defined in the DHCPv6   specification [6].3. Terminology   This document uses the terminology defined in RFC2460 [2] and the   DHCP specification [6].  In addition, this document uses the   following terms:   requesting router   The router that acts as a DHCP client and is                       requesting prefix(es) to be assigned.   delegating router   The router that acts as a DHCP server, and is                       responding to the prefix request.Troan & Droms          Expires September 1, 2003                [Page 3]Internet-Draft       IPv6 Prefix Options for DHCPv6           March 2003   Identity Association for Prefix Delegation (IA_PD) A collection of                       prefixes assigned to the requesting router.  Each                       IA_PD has an associated IAID.  A requesting                       router may have more than one IA_PD assigned to                       it; for example, one for each of its interfaces.4. Requirements   The keywords MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD,   SHOULD NOT, RECOMMENDED, MAY, and OPTIONAL, when they appear in this   document, are to be interpreted as described in RFC 2119 [1].5. Model and Applicability   The model of operation for prefix delegation is as follows.  A   delegating router is provided IPv6 prefixes to be delegated to   requesting routers.  Examples of ways in which the delegating router   may be provided these prefixes are given in Section 12.2.  A   requesting router requests prefix(es) from the delegating router, as   described in Section 12.1.  The delegating router chooses prefix(es)   for delegation, and responds with prefix(es) to the requesting   router.  The requesting router is then responsible for the delegated   prefix(es).  For example, the requesting router might assign a subnet   from a delegated prefix to one of its interfaces, and begin sending   router advertisements for the prefix on that link.   Each prefix has an associated valid and preferred lifetime, which   constitutes an agreement about the length of time over which the   requesting router is allowed to use the prefix.  A requesting router   can request an extension of the lifetimes on a delegated prefix and   is required to terminate the use of a delegated prefix if the valid   lifetime of the prefix expires.   This prefix delegation mechanism would be appropriate for use by an   ISP to delegate a prefix to a subscriber, where the delegated prefix   would possibly be subnetted and assigned to the links within the   subscriber's network.5.1 Example network architectureTroan & Droms          Expires September 1, 2003                [Page 4]Internet-Draft       IPv6 Prefix Options for DHCPv6           March 2003   Figure 1 illustrates a network architecture in which prefix   delegation could be used.                    +--------+                              \                    |  AAA   |                               \                    | server |                                \                    +---+----+                                 |                     ___|__________________                    |                    /                      \                   |                   |    ISP core network    |                  |                    \__________ ___________/                   |                               |                               | ISP                       +-------+-------+                       | network                       |  Aggregation  |                       |                       |    device     |                       |                       |  (delegating  |                       |                       |    router)    |                       |                       +-------+-------+                       |                               |                              /                               |DSL to subscriber            /                               |premises                    /                               |                        +------+------+                     \                        |     CPE     |                      \                        | (requesting |                       \                        |   router)   |                        |                        +----+---+----+                        |                             |   |                             | Subscriber      ---+-------------+-----+- -+-----+-------------+---      | network         |             |               |             |         |    +----+-----+ +-----+----+     +----+-----+ +-----+----+    |    |Subscriber| |Subscriber|     |Subscriber| |Subscriber|   /    |    PC    | |    PC    |     |    PC    | |    PC    |  /    +----------+ +----------+     +----------+ +----------+ /   Figure 1: An example of prefix delegation.   In this example an AAA server is configured with a prefix assigned to   the customer at the time of subscription to the ISP service.  The   prefix delegation process begins when the requesting router requests   configuration information through DHCP.  The DHCP messages from the   requesting router are received by the delegating router in the   aggregation device.  When the delegating router receives the request,   it consults the AAA server to authenticate and authorise the   requesting router.  The AAA server returns the subscriber's   prefix(es) in a Framed-IPv6-Prefix attribute as described in RFC 3162   [7], and the delegating router returns them to the requesting router.Troan & Droms          Expires September 1, 2003                [Page 5]Internet-Draft       IPv6 Prefix Options for DHCPv6           March 2003   The requesting router subnets the delegated prefix and assigns the   longer prefixes to links in the subscriber's network.  In a typical   scenario based on the network shown in Figure 1, the requesting   router subnets a single delegated /48 prefix into /64 prefixes and   assigns one /64 prefix to each of the links in the subscriber   network.   The prefix delegation options can be used in conjunction with other   DHCP options carrying other configuration information to the   requesting router.  The requesting router may, in turn, then provide   DHCP service to hosts attached to the internal network.  For example,   the requesting router may obtain the addresses of DNS and NTP servers   from the ISP delegating router, and then pass that configuration   information on to the subscriber hosts through a DHCP server in the   requesting router.6. Identity Association for Prefix Delegation   An IA_PD is a construct through which a delegating router and a   requesting router can identify, group and manage a set of related   IPv6 prefixes.  Each IA_PD consists of an IAID and associated   configuration information.  An IA_PD for prefixes is the equivalent   of an IA (described in DHCPv6 specification [6]) for addresses.   An IA_PD is different from an IA, in that it does not need to be   associated with exactly one interface.  One IA_PD can be associated   with the requesting router, with a set of interfaces or with exactly   one interface.  A requesting router 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 delegating router.   The IAID uniquely identifies the IA_PD and must be chosen to be   unique among the IA_PD IAIDs on the requesting router.  The IAID is   chosen by the requesting router.  For any given use of an IA_PD by   the requesting router, the IAID for that IA_PD MUST be consistent   across restarts of the requesting router.  The requesting router may   maintain consistency either by storing the IAID in non-volatile   storage or by using an algorithm that will consistently produce the   same IAID as long as the configuration of the requesting router has   not changed.  If the requesting router uses only one IAID, it can use   a well-known value, e.g zero.   The configuration information in an IA_PD consists of one or more   IPv6 prefixes along with the times T1 and T2 for the IA_PD.  See   section Section 9 for the representation of an IA_PD in a DHCP   message.Troan & Droms          Expires September 1, 2003                [Page 6]Internet-Draft       IPv6 Prefix Options for DHCPv6           March 20037. Overview of DHCP with Prefix Delegation   Prefix delegation with DHCP is independent of address assignment with   DHCP.  A requesting router can use DHCP for just prefix delegation or   for prefix delegation along with address assignment and other   configuration information.   A requesting router first creates an IA_PD and assigns it an IAID.   The requesting router then transmits a Solicit message containing an   IA_PD option describing the IA_PD.  Delegating routers that can   delegate prefixes to the IA_PD respond to the requesting router with   an Advertise message.   The requesting router may include prefixes in the IA_PDs as a hint to   the delegating router about specific prefixes for which the   requesting router has a preference.   When the requesting router has identified a delegating router, the   requesting router uses a Request message to populate the IA_PDs with   prefixes.  The requesting router includes one or more IA_PD options   in the Request message.  The delegating router returns prefixes and   other information about the IA_PDs to the requesting router in IA_PD   options in a Reply message.  The requesting router records the   lifetimes for the delegated prefix(es) and uses the prefix(es) as   described in the previous section.   Before the valid lifetime on each delegated prefix expires, the   requesting router includes the prefix in an IA_PD option sent in a   Renew message to the delegating router.  The delegating router   responds by returning the prefix with updated lifetimes to the   requesting router.8. Interface Selection   Delegated prefixes are not associated with a particular interface in