draft-ietf-dhc-dhcpv6-opt-prefix-delegation-02.txt

DHCPv6协议在Linux操作系统下的一个客户端实现。

11.1 Requesting router behaviour

   The requesting router uses a Request message to populate IA_PDs with
   prefixes.  The requesting router includes one or more IA_PD options
   in the Request message.  The delegating router then returns the
   prefixes for the IA_PDs to the requesting router in IA_PD options in
   a Reply message.

   The requesting router includes IA_PD options in any Renew, or Rebind
   messages sent by the requesting router.  The IA_PD option include all
   of the prefixes the requesting router currently has associated with
   that IA_PD.

   In some circumstances the requesting router may need verification
   that the delegating router still has a valid binding for the
   requesting router.  Examples of times when a requesting router may
   ask for such verification include:

   o  The requesting router reboots.

   o  The requesting router's upstream link flaps.

   o  The requesting router is physically disconnected from a wired
      connection.

   If such verification is needed the requesting router MUST initiate a
   Rebind/Reply message exchange as described in the section "Creation
   and Transmission of Rebind Messages" of the DHCP specification [6],
   with the exception that the retransmission parameters should be set
   as for the Confirm message, described in the section "Creation and
   Transmission of Confirm Messages" of the DHCP specification [6].  The
   requesting router includes any IA_PDs, along with prefixes associated
   with those IA_PDs in its Rebind message.

   Each prefix has valid and preferred lifetimes whose duration is
   specified in the IA_PD Prefix option for that prefix.  The requesting
   router uses Renew and Rebind messages to request the extension of the
   lifetimes of a delegated prefix.

   The requesting router uses a Release message to return a delegated
   prefix to a delegating router.  The prefixes to be released MUST be
   included in the IA_PDs.

   The Confirm and Decline message types are not used with Prefix
   Delegation.

   Upon the receipt of a valid Reply message, for each IA_PD the
   requesting router assigns a subnet from each of the delegated



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   prefixes to each of the links to which the associated interfaces are
   attached, with the following exception: the requesting router MUST
   NOT assign any delegated prefixes or subnets from the delegated
   prefix(es) to the link through which it received the DHCP message
   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.

11.2 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
   requesting router.  The mechanism through which the delegating router
   selects prefix(es) for delegation is not specified in this document.
   Section 10.2 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 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.  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.




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   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.

12. Prefix Delegation reconfiguration

   This section describes prefix delegation in Reconfigure message
   exchanges.

12.1 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).

12.2 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.

13. 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.

14. 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



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   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
   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.

15. IANA Considerations

   IANA is requested to assign option codes to these options from the
   option-code space as defined in section "DHCPv6 Options" of the
   DHCPv6 specification [6].

   IANA is requested to assign a status code to the NoPrefixAvail status
   code from the status-code space as defined in section "Status Codes"
   of the DHCPv6 specification [6].

16. 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.

17. Changes since revision-01

   o  Clarified the usage of how Preferred/Valid lifetimes should be
      used in Router Advertisements.

   o  Clarified the use of NoPrefixAvail in the case were the delegating
      router cannot delegate any prefixes.

   o  Use Rebind/Reply message exchange for binding confirmation rather
      than Renew/Reply.

Normative References

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



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   [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]


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

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





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