

Network Working Group                                           R. Droms
Internet-Draft                                             Cisco Systems
Expires: August 23, 2003                               February 22, 2003


     Results from Interoperability Tests of DHCPv6 Implementations
                  draft-ietf-dhc-dhcpv6-interop-00.txt

Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026.

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Copyright Notice

   Copyright (C) The Internet Society (2003).  All Rights Reserved.

Abstract

   This document publishes issues with the DHCPv6 protocols
   specifications, based on the results of interoperability testing
   among several implementations.

Introduction

   The DHCPv6 specification [1] has been accepted as a Proposed
   Standard, and several related specifications have been published and
   will soon be submitted to the IESG for review.  Several
   implementations of DHCPv6 have been completed, and these
   implementations have been tested for interoperability.




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   The purpose of this document is to provide a published record of the
   issues discovered through interoperability testing, for review and
   discussion by the appropriate IETF working groups.

   A course of action to correct problems with the DHCPv6 specifications
   is proposed for many of the listed issues.  Any changes to the
   specifications will be published to the appropriate working group
   mailing lists.

   The remainder of this documents lists specific issues, along with a
   summary of any discussion of the issue that has already occurred
   through e-mail and a proposed course of action to correct the issue.

   Throughout this document, unless otherwise qualified, section
   references and numbers refer to draft-ietf-dhc-dhcpv6-28.

1. Response of servers to Renew and Rebind messages, sections 18.2.3 and
   18.2.4

   Issue: Sections 18.2.3 and 18.2.4 have exactly the same sentence:

         If the server cannot find a client entry for the IA the server
         returns the IA containing no addresses with a Status Code
         option set to NoBinding in the Reply message.

      however, the semantics of "the server cannot find a client entry"
      is slightly different between the case of Renew and the case of
      Rebind.

   Discussion: A Renew message is sent to a specific server, which
      originally assigned the addresses in the IA.  If the server now
      does not have a record of the IA, it can authoritatively respond
      with a NoBinding Status Code.

      However, a Rebind message may be sent to more than one DHCP
      server, and the servers that did not originally assign the
      addresses in the IA may legitimately not have any record of the
      IA.  Therefore, in response to a Rebind message, the server should
      only respond if it can determine that the addresses are somehow
      invalid, and not respond if it simply has no record of the IA.

   Resolution: Leave the sentence in section 18.2.3 unchanged.  Replace
      the sentence in section 18.2.4 with the following text:

         If the server cannot find a client entry for the IA and the
         server determines that the addresses in the IA are not
         appropriate for the link to which the client's interface is
         attached according to the server's explicit configuration



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         information, the server MAY send a Reply message to the client
         containing the client's IA, with the lifetimes for the
         addresses in the IA set to zero.  This Reply constitutes an
         explicit notification to the client that the addresses in the
         IA are no longer valid.  In this situation, if the server does
         not send a Reply message it silently discards the Rebind
         message.


2. Correctness of T1 and T2 parameters

   Issue: What should a client or server do if it receives an IA_NA in a
      message where T1 > T2 > 0?

   Discussion: A client should ignore the IA_NA with the invalid T1 and
      T2 values.  A server should ignore the invalid T1 and T2 values
      and process the IA_NA as though the client did not set those
      values.

   Resolution: Add the following paragraphs at the end of section 22.4,
      "Identity Association for Non-temporary Addresses Option":

         If a server receives an IA_NA with T1 greater than T2, and both
         T1 and T2 are greater than 0, the server ignores the invalid
         values of T1 and T2 and processes the IA_NA as though the
         client had set T1 and T2 to 0.

         If a client receives an IA_NA with T1 greater than T2, and both
         T1 and T2 are greater than 0, the client discards the IA_NA
         option and processes the remainder of the message as though the
         server had not included the invalid IA_NA option.


3. Receipt of a Request message for an existing binding

   Issue: What should a server do when it receives a Request message
      that contains an IA for which the server already has a binding
      associating the IA with the requesting client (this can happen if
      the first Reply from a client is lost and the client resends the
      Request message)?

   Discussion: The server either updates the parameters and sends a new
      Reply or sends a cached copy of the previous Reply.

   Resolution: Add the following paragraph at the end of section 18.2.1:

       If the server finds that the client has included an IA in the
         Request message for which the server already has binding that



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         associates the IA with the client, the client has resent a
         Request message for which it did not receive a Reply message.
         The server either resends a previously cached Reply message or
         sends a new Reply message.


4. Client response to receipt of Reply with IA containing Status Code of
   NoAddrsAvail

   Issue: Section 18.1.8 describes the client's behavior:

         When the client receives a NoAddrsAvail status from the server
         in response to a Request, the client can either try another
         server (perhaps restarting the DHCP server discovery process)
         or use the Information-Request to obtain configuration
         parameters only.

      What does the client do if it receives more than one IA, and some
      IAs have been assigned addresses, while other IAs have been
      returned with status NoAddrsAvail?

   Discussion: The client should examine and process each IA
      individually.

   Resolution: Replace the text in question with:

         The client examines the status code in each IA individually.
         If the status code is NoAddrsAvail, the client has received no
         usable addresses in the IA and may choose to try obtaining
         addresses for the IA from another server.  The client uses
         addresses and other information from any IAs that do not
         contain a Status Code option with the NoAddrsAvail code.  If
         the client receives no addresses in any of the IAs, it may
         either try another server (perhaps restarting the DHCP server
         discovery process) or use the Information-request message to
         obtain other configuration information only.


5. Client processing of an IA option that does not include all addresses
   sent by the client

   Issue: Section 18.1.3 says:

         The client includes an IA option with all addresses currently
         assigned to the IA in its Renew message.

      and Section 18.2.3 has corresponding sentence:




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         If the server finds that any of the addresses are not
         appropriate to the link to which the client is attached, the
         server returns the address to the client with lifetimes of 0.

      If the server finds the addresses in the IA for the client then
      the server sends back the IA to the client with new lifetimes and
      T1/T2 times.  The server may choose to change the list of
      addresses and the lifetimes of addresses in IAs that are returned
      to the client.  That is,:

      *  the client sends all addresses for an IA to be renewed.

      *  (if the binding is still valid) the server returns all the
         addresses for the IA with 0 or larger lifetimes.

      What does the client do if an address it sent to the server is not
      included in the IA in the Reply message from the server?

   Discussion: The client leaves addresses in its IA, leaving the
      lifetimes on those addresses unchanged.  The client then discards
      the addresses when their lifetimes expire.

   Resolution: Add the following item to the bullet list in section
      18.1.8:

         - Leave unchanged any information about addresses the client
         has recorded in the IA but that were not included in the IA
         from the server

      Add the following text to the end of the last paragraph of section
      10:

         Additionally, when the valid lifetime for an address in an IA
         expires, the client MUST remove the address from the IA.


6. Receipt of Reply with Rapid Commit option after sending Request

   Issue: Section 17.1.4 says:

         If it does not receive such a Reply message and does receive a
         valid Advertise message, the client processes the Advertise
         message as described in section 17.1.3.

      What should the client do if it receives a Reply message for a
      Solicit message with a Rapid Commit option after SOL_TIMEOUT has
      expired and the client has sent a Request message?  Should the
      client ignore or accept it?  In the latter case, what happens if



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      the client has already sent a Request message (for which it will
      receive a different Reply message)?

   Discussion: The client can either discard the Reply message or
      process the Reply message and discard any subsequent Reply
      messages received in response to the Request message.

   Resolution: Add the following text to the end of section 17.1.4:

         If the client subsequently receives a valid Reply message that
         includes a Rapid Commit option, it either:

            processes the Reply message as described in section 18.1.8,
            and discards any Reply messages received in response to the
            Request message

            processes any Reply messages received in response to the
            Request message and discards the Reply message that includes
            the Rapid Commit option


7. Inconsistent or incorrect text in section 15

   Issue: Text in section 15 is inconsistent, ambiguous and incorrect.

   Discussion: For example, in section 15.6:

         Servers MUST discard any received Renew message that meets any
         of the following conditions:

         +  the message MUST include a Server Identifier option

         +  the contents of the Server Identifier option MUST match the
            server's identifier

         +  ...

      However, there should be a wording problem.  The first sentence
      should read:

         Servers MUST discard any received Renew message that fails to
         meet any of the following conditions:

   Resolution: Review and reword appropriate text in section 15 for
      consistency and correctness.






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8. Typographic error regarding MRC in section 18.1.6

   Issue: In the following line of Section 18.1.6:

         MRC   REL_MAX_MRC

      should be:

         MRC   REL_MAX_RC

   Resolution: Correct typo in section 18.1.6.


9. Inconsistent lifetimes for an address

   Issue: What should a client or server do if the preferred lifetime is
      larger than the valid lifetime for an IA address option in a reply
      message (to request/renew, etc)?  Similarly, suppose either T1 or
      T2 is larger than the shortest preferred lifetime in the IA?

   Discussion: A client discards any addresses for which the preferred
      lifetime is larger than the valid lifetime.  It is acceptable for
      T1 or T2 to be larger than a preferred or valid lifetime when the
      server does not expect to extend the lifetime of that address in
      the future.  A server ignores any invalid or inconsistent
      lifetimes or values for T1 and T2 and processes the IA as though
      the client had not set those invalid or inconsistent values.

      In a related matter, the text in section 22.4 that gives
      recommended values for T1 and T2 should be clarified to indicate
      that T1 and T2 should be based on shortest lifetime of any address
      that the server intends to extend in the future.

   Resolution: Add the following paragraph before the next-to-last
      paragraph of section 22.6 (bottom of page 65 in draft-ietf-dhc-
      dhcpv6-28.txt):

         A client discards any addresses for which the preferred
         lifetime is greater than the valid lifetime.  A server ignores
         the lifetimes set by the client if the preferred lifetime is
         greater than the valid lifetime and ignores the values for T1
         and T2 set by the client if those values are greater than the
         preferred lifetime.

      Change the second sentence of the last paragraph of section 22.4
      to:

         Recommended values for T1 and T2 are .5 and .8 times the



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         shortest preferred lifetime of the addresses in the IA that the
         server is willing to extend, respectively.


10. "Infinity" as a time value

   Issue: Should DHCPv6 have a notion of "infinity" as lifetimes and
      T1/T2 values?  In RFC2461 [2], 0xffffffff is taken to mean
      "infinity".  If DHCPv6 intends to be consistent with that meaning,
      there should be an explicit definition somewhere in the
      specification.

   Discussion: DHCPv6 should treat 0xffffffff as "infinity" in the case
      of time values.  In section 22.4, the recommendations for values
      of T1 and T2 need to be clarified for the case when the lifetimes
      of the addresses in an IA are 0xffffffff.

   Resolution: Add section 5.6:

         5.6 Representation of time values and "Infinity" as a time
         value

            All time values for lifetimes, T1 and T2 are unsigned
            integers.  The value 0xffffffff is taken to mean "infinity"
            when used as a lifetime (as in RFC2461 [17]) or a value for
            T1 or T2.

         Add the following sentence after the sentence in the last
         paragraph of section 22.4 that begins "Recommended values...":

            If the "shortest" preferred lifetime is 0xffffffff
            ("infinity"), the recommended T1 and T2 values are also
            0xffffffff.

         Add the following paragraph at the end of section 22.4:

            Care should be taken in setting T1 or T2 to 0xffffffff
            ("infinity").  A client will never attempt to extend the
            lifetimes of any addresses in an IA with T1 set to
            0xffffffff.  A client will never attempt to use a Rebind
            message to locate a different server to extend the lifetimes
            of any addresses in an IA with T2 set to 0xffffffff.

         Add the following paragraph before the next-to-last paragraph
         of section 22.6 (bottom of page 65 in draft-ietf-dhc-dhcpv6-
         28.txt, after the paragraph added in Section 9 of this
         document):




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            Care should be taken in setting the valid lifetime of an
            address to 0xffffffff ("infinity"), which amounts to a
            permanent assignment of an address to a client.


11. Client behavior in response to receipt of Reply message with
    StatusCode set to NoBinding

   Issue: In section 18.1.8, it's not clear if the client should
      continue to send Renew/Rebind messages as well as send a Request
      message in response to a Reply with a Status Code set to
      NoBinding.

   Discussion: For each IA in the original Renew/Rebind, the client
      should:

      *  send a Request if the StatusCode in the IA is NoBinding

      *  send a Renew/Rebind if the IA is not in the Reply

      *  accept the response if the IA is in the Reply and there is no
         status code

   Resolution: Change the text in the corresponding (third-to-last)
      paragraph in section 18.1.8 to read:

         When the client receives a Reply message in response to a Renew
         or Rebind message, the client examines each IA independently.
         For each IA in the original Renew or Rebind message, the
         client:

         +  sends a Request message if the StatusCode in the IA is
            NoBinding (and does not send any additional Renew/Rebind
            messages)

         +  sends a Renew/Rebind if the IA is not in the Reply message

         +  otherwise accepts the information in the IA


12. Maximum value for Elapsed Time option

   Issue: The value carried in the Elapsed Time option is an unsigned,
      16 bit integer with a resolution of 1/100 of a second.  The
      maximum time that can be represented in this format is roughly 11
      minutes.  What happens if the client's elapsed time exceeds the
      maximum value that can be represented in the Elapsed Time option?




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   Discussion: The value 0xffff should be used to represent any elapsed
      time value greater than the maximum time that can be represented
      in the Elapsed Time option.

   Resolution: Add the following sentence to the end of section 22.9:

         The elapsed time value is an unsigned, 16 bit integer.  The
         client uses the value 0xffff to represent any elapsed time
         values greater than the largest time value that can be
         represented in the Elapsed Time option.


13. Appearance of Elapsed Time option in DHCP messages

   Issue: The table in Appendix A shows (incorrectly) that the Elapsed
      Time option may appear in Advertise and Reply messages.

   Discussion: A server should not include an Elapsed Time option in
      Advertise and Reply messages.

   Resolution: Edit the table in Appendix A.


14. Acknowledgments

   Thanks to Tatuya Jinmei for identifying many of these issues and for
   contributing to the discussion and resolution of the issues.  This
   document was reviewed and discussed by Jim Bound, Ralph Droms, Tatuya
   Jinmei, Ted Lemon, Ole Troan, Bernie Volz and Jun Xie.

References

   [1]  Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C. and M.
        Carney, "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)",
        draft-ietf-dhc-dhcpv6-28 (work in progress), November 2002.

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













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Author's Address

   Ralph Droms
   Cisco Systems
   300 Apollo Drive
   Chelmsford  01824
   MA

   Phone: +1 978.497.4733
   EMail: rdroms@cisco.com









































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