draft-ietf-dhc-dhcpv6-opt-prefix-delegation-03.txt

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   from the delegating router.

   When a requesting router subnets a delegated prefix, it must assign
   additional bits to the prefix to generate unique, longer prefixes.
   For example, if the requesting router in Figure 1 were delegated
   3FFE:FFFF:0::/48, it might generate 3FFE:FFFF:0:1::/64 and
   3FFE:FFFF:0:2::/64 for assignment to the two links in the subscriber
   network.  If the requesting router were delegated 3FFE:FFFF:0::/48
   and 3FFE:FFFF:1::/48, it might assign 3FFE:FFFF:0:1::/64 and
   3FFE:FFFF:1:1::/64 to one of the links, and 3FFE:FFFF:0:2::/64 and
   3FFE:FFFF:1:2::/64 for assignment to the other link.

   If the requesting router assigns a delegated prefix to a link to
   which the router is attached, and begins to send router
   advertisements for the prefix on the link, the requesting router MUST
   set the valid lifetime in those advertisements to be no later than
   the valid lifetime specified in the IA_PD Prefix option.  A
   requesting router MAY use the preferred lifetime specified in the
   IA_PD Prefix option.

   Handling of Status Codes options in received Reply messages is
   described in "Receipt of Reply Messages" of the DHCP specification
   [6].  The NoPrefixAvail Status Code is handled in the same manner as
   the NoAddrsAvail Status Code.

12.2 Delegating Router behaviour

   When a delegating router receives a Request message from a requesting
   router that contains an IA_PD option, and the delegating router is
   authorised to delegate prefix(es) to the requesting router, the
   delegating router selects the prefix(es) to be delegated to the



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   requesting router.  The mechanism through which the delegating router
   selects prefix(es) for delegation is not specified in this document.
   Section 11.2 gives examples of ways in which a delegating router
   might select the prefix(es) to be delegated to a requesting router.

   A delegating router examines the prefix(es) identified in IA_PD
   Prefix options (in an IA_PD option) in Renew and Rebind messages and
   responds according to the current status of the prefix(es).  The
   delegating router returns IA_PD Prefix options (within an IA_PD
   option) with updated lifetimes for each valid prefix in the message
   from the requesting router.  If the delegating router finds that any
   of the prefixes are not in the requesting router's binding entry, the
   delegating router returns the prefix to the requesting router with
   lifetimes of 0.

   Behaviour in the case where the delegating router cannot find a
   binding for the requesting router's IA_PD:

   Renew message       If the delegating router cannot find a binding
                       for the requesting router's IA_PD the delegating
                       router returns the IA_PD containing no prefixes
                       with a Status Code option set to NoBinding in the
                       Reply message.

   Rebind message      If the delegating router cannot find a binding
                       for the requesting router's IA_PD and the
                       delegating router determines that the prefixes in
                       the IA_PD are not appropriate for the link to
                       which the requesting router's interface is
                       attached according to the delegating routers
                       explicit configuration, the delegating router MAY
                       send a Reply message to the requesting router
                       containing the IA_PD with the lifetimes of the
                       prefixes in the IA_PD set to zero.  This Reply
                       constitutes an explicit notification to the
                       requesting router that the prefixes in the IA_PD
                       are no longer valid.  If the delegating router is
                       unable to determine if the prefix is not
                       appropriate for the link, the Rebind message is
                       discarded.

   A delegating router may mark any prefix(es) in IA_PD Prefix options
   in a Release message from a requesting router as "available",
   dependent on the mechanism used to acquire the prefix, e.g in the
   case of a dynamic pool.

   The delegating router MUST include an IA_PD Prefix option or options
   (in an IA_PD option) in Reply messages sent to a requesting router.



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13. Prefix Delegation reconfiguration

   This section describes prefix delegation in Reconfigure message
   exchanges.

13.1 Delegating Router behaviour

   The delegating router initiates a configuration message exchange with
   a requesting router, as described in the section "DHCP Server-
   Initiated Configuration Exchange" of the DHCP specification [6].  The
   delegating router specifies the IA_PD option in the Option Request
   option to cause the requesting router to include an IA_PD option to
   obtain new information about delegated prefix(es).

13.2 Requesting Router behaviour

   The requesting router responds to a Reconfigure message received from
   a delegating router as described in the DHCP specification [6].  The
   requesting router MUST include the IA_PD Prefix option(s) (in an
   IA_PD option) for prefix(es) that have been delegated to the
   requesting router by the delegating router from which the Reconfigure
   message was received.

14. Relay agent behaviour

   A relay agent forwards messages containing Prefix Delegation options
   in the same way as described in section "Relay Behaviour" of the DHCP
   specification [6].

   If a delegating router communicates with a requesting router through
   a relay agent, the delegating router may need a protocol or other
   out-of-band communication to add routing information for delegated
   prefixes into the provider edge router.

15. Security Considerations

   Security considerations in DHCP are described in the section
   "Security Considerations" of the DHCP specification [6].

   A rogue delegating router can issue bogus prefixes to a requesting
   router.  This may cause denial of service due to unreachability.

   An intruder requesting router may be able to mount a denial of
   service attack by repeated requests for delegated prefixes that
   exhaust the delegating router's available prefixes.

   To guard against attacks through prefix delegation, requesting
   routers and delegating routers SHOULD use DHCP authentication as



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   described in section "Authentication of DHCP messages" in the DHCP
   specification [6].  For point to point links, where one trusts that
   there is no man in the middle, or one trusts layer two
   authentication, DHCP authentication or IPsec may not be necessary.
   Because a requesting router and delegating routers must each have at
   least one assigned IPv6 address, the routers may be able to use IPsec
   for authentication of DHCPv6 messages.  The details of using IPsec
   for DHCPv6 are under development.

16. IANA Considerations

   IANA is requested to assign option codes to:

   OPTION_IA_PD

   OPTION_IAPREFIX

   from the option-code space as defined in section "DHCPv6 Options" of
   the DHCPv6 specification [6].

   IANA is requested to assign a status code:

   NoPrefixAvail       Delegating router has no prefixes available to
                       assign to the IAPD(s)

   from the status-code space as defined in section "Status Codes" of
   the DHCPv6 specification [6].

17. Acknowledgements

   Thanks for the input and review by (in alphabetical order) Steve
   Deering, Dave Forster, Brian Haberman, Tatuya Jinmei, Shin Miyakawa,
   Pekka Savola, Bernie Volz, Trevor Warwick and Toshi Yamasaki.

18. Changes in draft-ietf-dhc-dhcpv6-opt-prefix-delegation-03

   o  Clarified that this draft is an extension of the DHCPv6
      specification and that complete specification and terminology can
      be found in the DHCPv6 specification.

   o  Updated relevant sections to be consistent with draft-ietf-dhc-
      dhcpv6-interop-00.txt.  This includes T1/T2 times, preferred and
      valid lifetimes and Rebind/Renew usage.

   o  Clarified the usage of the NoPrefixAvail Status Code

   o  Clarified delegating router behaviour when no binding is found for
      Renew/Rebind.



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   o  Various editorial changes

Normative References

   [1]  Bradner, S., "Key words for use in RFCs to Indicate Requirement
        Levels", BCP 14, RFC 2119, March 1997.

   [2]  Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6)
        Specification", RFC 2460, December 1998.

   [3]  Narten, T., Nordmark, E. and W. Simpson, "Neighbor Discovery for
        IP Version 6 (IPv6)", RFC 2461, December 1998.

   [4]  Hinden, R. and S. Deering, "IP Version 6 Addressing
        Architecture", RFC 2373, July 1998.

   [5]  Thomson, S. and T. Narten, "IPv6 Stateless Address
        Autoconfiguration", RFC 2462, December 1998.

   [6]  Droms, R., "Dynamic Host Configuration Protocol for IPv6
        (DHCPv6)", draft-ietf-dhc-dhcpv6-28 (work in progress), November
        2002.

   [7]  Aboba, B., Zorn, G. and D. Mitton, "RADIUS and IPv6", RFC 3162,
        August 2001.

Informative References

   [8]  Miyakawa, S., "Requirements for IPv6 prefix delegation", draft-
        ietf-ipv6-prefix-delegation-requirement-00 (work in progress),
        November 2002.


Authors' Addresses

   Ole Troan
   Cisco Systems
   250 Longwater Avenue
   Reading  RG2 6GB
   United Kingdom

   Phone: [phone]
   EMail: [e-mail]








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   Ralph Droms
   Cisco Systems
   300 Apollo Drive
   Chelmsford, MA  01824
   USA

   Phone: [phone]
   EMail: [e-mail]











































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