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Versions: (draft-troan-dhc-dhcpv6-stateful-issues) 00 01 02 03 04 05 06 07 08 09 10 11 12 RFC 7550

Network Working Group                                           O. Troan
Internet-Draft                                                   B. Volz
Updates: 3315,3633 (if approved)                     Cisco Systems, Inc.
Intended status: Standards Track                            M. Siodelski
Expires: May 30, 2015                                                ISC
                                                       November 26, 2014


    Issues and Recommendations with Multiple Stateful DHCPv6 Options
              draft-ietf-dhc-dhcpv6-stateful-issues-09.txt

Abstract

   Dynamic Host Configuration Protocol for IPv6 (DHCPv6) was not written
   with the expectation that additional stateful DHCPv6 options would be
   developed.  IPv6 Prefix Options for Dynamic Host Configuration
   Protocol (DHCP) version 6 has since shoe-horned a new option for
   Prefix Delegation into DHCPv6.  Implementation experience of the CPE
   model described in RFC 7084 has shown multiple issues with the DHCPv6
   protocol in supporting multiple stateful options.  This document
   updates RFC 3315 and RFC 3633 to address the identified issues.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   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."

   This Internet-Draft will expire on May 30, 2015.

Copyright Notice

   Copyright (c) 2014 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents



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   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   4.  Handling of Multiple IA Options Types . . . . . . . . . . . .   3
     4.1.  Placement of Status Codes . . . . . . . . . . . . . . . .   4
     4.2.  Advertise Message . . . . . . . . . . . . . . . . . . . .   6
     4.3.  T1/T2 Timers  . . . . . . . . . . . . . . . . . . . . . .   7
     4.4.  Renew and Rebind Messages . . . . . . . . . . . . . . . .   8
       4.4.1.  Renew Message . . . . . . . . . . . . . . . . . . . .   8
       4.4.2.  Rebind Message  . . . . . . . . . . . . . . . . . . .   8
       4.4.3.  Updates to section 18.1.3 of RFC 3315 . . . . . . . .   9
       4.4.4.  Updates to Section 18.1.4 of RFC 3315 . . . . . . . .  10
       4.4.5.  Updates to Section 18.1.8 of RFC 3315 . . . . . . . .  11
       4.4.6.  Updates to Section 18.2.3 of RFC 3315 . . . . . . . .  13
       4.4.7.  Updates to Section 18.2.4 of RFC 3315 . . . . . . . .  15
       4.4.8.  Updates to RFC 3633 . . . . . . . . . . . . . . . . .  17
     4.5.  Confirm Message . . . . . . . . . . . . . . . . . . . . .  18
     4.6.  Decline Should Not Necessarily Trigger a Release  . . . .  19
     4.7.  Multiple Provisioning Domains . . . . . . . . . . . . . .  19
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  19
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  19
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  19
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  19
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  19
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  20
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  20

1.  Introduction

   DHCPv6 [RFC3315] was not written with the expectation that additional
   stateful DHCPv6 options would be developed.  DHCPv6 Prefix Delegation
   [RFC3633] has since shoe-horned a new option for Prefix Delegation
   into DHCPv6.  Implementation experience of the CPE model described in
   [RFC7084] has shown issues with the DHCPv6 protocol in supporting
   multiple stateful option types, in particular IA_NA (non-temporary
   addresses) and IA_PD (delegated prefixes).

   This document describes a number of problems encountered with
   coexistence of the IA_NA and IA_PD option types and changes to the
   DHCPv6 protocol specifications to address these problems.



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   The intention of this work is to clarify and, where needed, modify
   the DHCP protocol specification to support IA_NA and IA_PD option
   types within a single DHCP session.

   Note that while IA_TA (temporary addresses) options may be included
   with other IA option type requests, these generally are not renewed
   (there are no T1/T2 times) and have a separate life cycle from IA_NA
   and IA_PD option types.  DHCPv6 assigned temporary addresses also
   have limited value when DHCPv6 is used for non-temporary address
   assignment, as the privacy issues identified for IPv6 stateless
   address assignment ([RFC4941]) do not apply to DHCPv6 assignments.
   Therefore, the IA_TA option type is mostly out of scope for this
   document.

   The changes described in this document are intended to be
   incorporated in a new revision of the DHCPv6 protocol specification
   ([I-D.dhcwg-dhc-rfc3315bis]).

2.  Conventions

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

3.  Terminology

   In addition to the terminology defined in [RFC3315], [RFC3633], and
   [RFC7227], the following terminology is used in this document:

   Identity association (IA):      Throughout this document, "IA" is
                                   used to refer to the Identity
                                   Association containing addresses or
                                   prefixes assigned to a client and
                                   carried in the IA_NA or IA_PD options
                                   respectively.

   IA option types:                This is used to generally mean an
                                   IA_NA and/or IA_PD option.

   Stateful options:               Options that require dynamic binding
                                   state per client on the server.

4.  Handling of Multiple IA Options Types

   DHCPv6 was written with the assumption that the only stateful options
   were for assigning addresses.  DHCPv6 PD describes how to extend the
   DHCPv6 protocol to handle prefix delegation, but [RFC3633] did not




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   consider how DHCP address assignment and prefix delegation could co-
   exist.

   If a client requests multiple IA option types, but the server is
   configured to only offer a subset of them, the client could react in
   several ways.  Reset the state machine and continue to send Solicit
   messages, create separate DHCP sessions for each IA option type and
   continue to Solicit for the unfulfilled IA options, or it could
   continue with the single session, and include the unfulfilled IA
   options in subsequent messages to the server.

   Reseting the state machine and continuing to send Solicit messages
   may result in the client never completing DHCP and is generally not
   considered a good solution.  It can also result in a request storm if
   the client does not appropriately rate limit its sending of Solicit
   messages.

   Creating a separate DHCP session (separate instances of the client
   state machine) per IA option type, while conceptually simple, has a
   number of issues: multiple instances of the state machine in clients,
   additional DHCP protocol traffic, 'collisions' between other
   configuration options, divergence in that each IA option type
   specification specifies its 'own' version of the DHCP protocol.

   This leaves a single DHCP session and state machine which is the
   proposed solution.  Here, the client can use what it is able to
   obtain and can continue to request what it was previously unable to
   obtain while maintaining a single session and state machine.

   Proposed solution: the client should keep a single session with the
   server and include the missing options in subsequent messages
   (Request, Renew, and Rebind) to the server.

4.1.  Placement of Status Codes

   In Reply messages IA specific status codes (i.e., NoAddrsAvail,
   NotOnLink, NoBinding, NoPrefixAvail) are encapsulated in the IA
   option.  In Advertise messages the Status Code option with the
   NoAddrsAvail code is in the top level.  This makes sense if the
   client is only interested in the assignment of the addresses and the
   failure case is fatal.  However, if the client sends both IA_NA and
   IA_PD options in a Solicit message, it is possible that the server
   offers no addresses but it offers some prefixes, and the client may
   choose to send a Request message to obtain the offered prefixes.  In
   this case, it is better if the Status Code option for IA specific
   status codes is encapsulated in the IA option to indicate that the
   failure occurred for the specific IA.  This also makes the




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   NoAddrsAvail and NoPrefixAvail Status Code option placement for
   Advertise messages identical to Reply messages.

   In addition, how a server formats the Advertise message when
   addresses are not available has been a point of some confusion and
   implementations seem to vary (some strictly follow RFC 3315 while
   others assumed it was encapsulated in the IA option as for Reply
   messages).

   Therefore, the proposed solution is:

   Clients MUST be prepared to handle each of the following Advertise
   messages formats when there are no addresses available (even when no
   other IA option types were in the Solicit):

   1.  Advertise containing just a top-level Status Code option (of
       NoAddrsAvail) and no IA_NAs/IA_TAs.

   2.  Advertise containing the IA_NAs and/or IA_TAs with encapsulated
       Status Code option (of NoAddrsAvail) and no top-level Status Code
       option.

   3.  Advertise containing a top-level Status Code option (of
       NoAddrsAvail) and IA_NAs and/or IA_TAs with a Status Code option
       (of NoAddrsAvail).

   Servers MUST return the Status Code option (of NoAddrsAvail)
   encapsulated in an IA_NA/IA_TA options and not as a top-level Status
   Code option (of NoAddrsAvail) when no addresses will be assigned (2
   in the above list).  This means that the Advertise response matches
   the Reply response with respect to the handling of the NoAddrsAvail
   status.

   Replace the following paragraph in RFC 3315, section 17.2.2:

      If the server will not assign any addresses to any IAs in a
      subsequent Request from the client, the server MUST send an
      Advertise message to the client that includes only a Status
      Code option with code NoAddrsAvail and a status message for
      the user, a Server Identifier option with the server's DUID,
      and a Client Identifier option with the client's DUID.

   With:








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      If the server will not assign any addresses to an IA in a
      subsequent Request from the client, the server MUST include
      the IA in the Advertise message with no addresses in the IA
      and a Status Code option encapsulated in the IA containing
      status code NoAddrsAvail.

4.2.  Advertise Message

   [RFC3315] specifies that a client must ignore an Advertise message if
   a server will not assign any addresses to a client.  A client
   requesting both IA_NA and IA_PD, with a server that only offers one
   of them, is not supported in the current protocol specification.

   Proposed solution: a client SHOULD accept Advertise messages, even
   when not all IA option types are being offered.  And, in this case,
   the client SHOULD include the not offered IA option types in its
   Request.  A client SHOULD only ignore an Advertise message when all
   IA options include no offered addresses or delegated prefixes.  Note
   that ignored messages MUST still be processed for SOL_MAX_RT and
   INF_MAX_RT options as specified in [RFC7083].

   Replace Section 17.1.3 of RFC 3315: (existing errata)

     The client MUST ignore any Advertise message that includes a Status
     Code option containing the value NoAddrsAvail, with the exception
     that the client MAY display the associated status message(s) to the
     user.

   With (this includes the changes made by [RFC7083]):

     The client MUST ignore any Advertise message that contains no
     addresses (IAADDR options encapsulated in IA_NA or IA_TA options)
     and no delegated prefixes (IAPREFIX options encapsulated in IA_PD
     options, see RFC 3633) with the exception that the client
     MUST process an included SOL_MAX_RT option (RFC 7083), MUST
     process an included INF_MAX_RT option (RFC 7083), and MAY
     display any associated status message(s) to the user.

   And, replace:

     -  The client MAY choose a less-preferred server if that server
        has a better set of advertised parameters, such as the
        available addresses advertised in IAs.

   With:






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     -  The client MAY choose a less-preferred server if that server
        has a better set of advertised parameters, such as the
        available options advertised in IAs.

   It is important to note that the receipt of an Advertise message
   without any addresses and delegated prefixes does not imply that the
   client should restart the Solicit retransmissions timers.  Doing so
   would lead to a Solicit/Advertise storm.

4.3.  T1/T2 Timers

   The T1 and T2 times determine when the client will contact the server
   to extend lifetimes of information received in an IA.  How should a
   client handle the case where multiple IA options have different T1
   and T2 times?

   In a multiple IA option type model, the T1/T2 times are protocol
   timers, that should be independent of the IA options themselves.  If
   we were to redo the DHCP protocol from scratch the T1/T2 times should
   be carried in a separate DHCP option.

   Proposed solution: The server MUST set the T1/T2 times in all IA
   options in a Reply or Advertise message to the same value.  To deal
   with the case where servers have not yet been updated to do that, the
   client MUST select a T1 and T2 time from all IA options which will
   guarantee that the client will send Renew/Rebind messages not later
   than at the T1/T2 times associated with any of the client's bindings.

   As an example, if the client receives a Reply with T1_NA of 3600 /
   T2_NA of 5760 and T1_PD of 0 / T2_PD of 1800, the client SHOULD use
   the T1_PD of 0 / T2_PD of 1800.  The reason for this is that a T1 of
   0 means that the Renew time is at the client's discretion, but this
   value cannot be greater than the T2 value (1800).

   The following paragraph should be added to Sections 18.2.1, 18.2.3,
   and 18.2.4 of RFC 3315:

     The T1/T2 times set in each applicable IA option for a Reply MUST
     be the same values across all IAs.  The server MUST determine the
     T1/T2 times across all of the applicable client's bindings in the
     Reply.  This facilitates the client being able to renew all of the
     bindings at the same time.

   Note: This additional paragraph has also been included in the revised
   text later for Sections 18.2.3 and 18.2.4 of RFC 3315.

   Changes for client T1/T2 handling are included in Section 4.4.3 and
   Section 4.4.4.



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4.4.  Renew and Rebind Messages

   This section presents issues with handling multiple IA option types
   in the context of creation and processing the Renew and Rebind
   messages.  It also proposes relevant updates to the [RFC3315] and
   [RFC3633].

4.4.1.  Renew Message

   The Renew message, as described in [RFC3315], allows a client to only
   renew bindings assigned via a Request message.

   In a multiple IA option type model, the Renew does not support the
   ability for the client to renew one IA option type while requesting
   bindings for other IA option types that were not available when the
   client sent the Request.

   Proposed solution: The client should continue with the IA options
   received, while continuing to include the other IA options in
   subsequent messages to the server.  The client and server processing
   need to be modified.  Note that this change makes the server's IA
   processing of Renew similar to the Request processing.

4.4.2.  Rebind Message

   In Section 4.4.1 it has been proposed that the client includes IA
   options in a Renew message for the bindings it desires but has been
   unable to obtain by sending a Request message, apart from the IA
   options for the existing bindings.

   At time T2, the client stops sending Renew messages to the server and
   initiates the Rebind/Reply message exchange with any available
   server.  In this case, it should be possible to continue trying to
   obtain new bindings using the Rebind message if the client failed to
   get the response from the server to the Renew message.

   The Rebind message, as described in [RFC3315] does not explicitly
   specify what a server should do when an IA option which contains no
   addresses is present.

   Proposed solution: The client should continue with the IA options
   received and it MAY include additional IA options to request creation
   of additional bindings.








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4.4.3.  Updates to section 18.1.3 of RFC 3315

   Replace Section 18.1.3 of RFC 3315 with the following text:

     To extend the valid and preferred lifetimes for the addresses
     associated with an IA, the client sends a Renew message to the
     server from which the client obtained the addresses in the IA
     containing an IA option for the IA.  The client includes IA Address
     options in the IA option for the addresses associated with the IA.
     The server determines new lifetimes for the addresses in the IA
     according to the administrative configuration of the server.  The
     server may also add new addresses to the IA.  The server may remove
     addresses from the IA by setting the preferred and valid lifetimes
     of those addresses to zero.

     The server controls the time at which the client contacts the
     server to extend the lifetimes on assigned addresses through the T1
     and T2 parameters assigned to an IA.  However, as the client
     Renews/Rebinds all IAs from the server at the same time, the client
     MUST select a T1 and T2 time from all IA options which will
     guarantee that the client will send Renew/Rebind messages not later
     than at the T1/T2 times associated with any of the client's
     bindings.

     At time T1, the client initiates a Renew/Reply message exchange to
     extend the lifetimes on any addresses in the IA.

     If T1 or T2 had been set to 0 by the server (for an IA_NA) or there
     are no T1 or T2 times (for an IA_TA) in a previous Reply, the
     client may send a Renew or Rebind message, respectively, at the
     client's discretion.

     The client sets the "msg-type" field to RENEW.  The client
     generates a transaction ID and inserts this value in the
     "transaction-id" field.

     The client places the identifier of the destination server in a
     Server Identifier option.

     The client MUST include a Client Identifier option to identify
     itself to the server.  The client adds any appropriate options,
     including one or more IA options.

     The client includes an IA option with all addresses currently
     assigned to the IA in its Renew message.  The client also includes
     IA options for all other bindings for which the client desires to
     extend the lifetimes of addresses.  The client MUST only include




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     addresses in the IA that the client obtained from the server and
     are still valid (have non-zero lifetime).

     The client MAY include an IA option for each binding it desires but
     has been unable to obtain.  This IA option MUST NOT contain any
     addresses.  However, it MAY contain the IA Address option with IPv6
     address field set to 0 to indicate the client's preference for the
     preferred and valid lifetimes for any newly assigned addresses.

     The client MUST include an Option Request option (see section 22.7)
     to indicate the options the client is interested in receiving.  The
     client MAY include options with data values as hints to the server
     about parameter values the client would like to have returned.

     The client transmits the message according to section 14, using the
     following parameters:

        IRT     REN_TIMEOUT

        MRT     REN_MAX_RT

        MRC     0

        MRD     Remaining time until T2

     The message exchange is terminated when time T2 is reached (see
     section 18.1.4), at which time the client begins a Rebind message
     exchange.

4.4.4.  Updates to Section 18.1.4 of RFC 3315

   Replace Section 18.1.4 of RFC 3315 with the following text:

     At time T2 (which will only be reached if the server to which the
     Renew message was sent at time T1 has not responded), the client
     initiates a Rebind/Reply message exchange with any available
     server.

     The client constructs the Rebind message as described in 18.1.3
     with the following differences:

     -  The client sets the "msg-type" field to REBIND.

     -  The client does not include the Server Identifier option in the
        Rebind message.

     The client transmits the message according to section 14, using the
     following parameters:



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        IRT     REB_TIMEOUT

        MRT     REB_MAX_RT

        MRC     0

        MRD     Remaining time until valid lifetimes of all addresses in
                all IAs have expired

     If all addresses for an IA have expired the client may choose to
     include this IA without any addresses (or with only a hint for
     lifetimes) in subsequent Rebind messages to indicate that the
     client is interested in assignment of the addresses to this IA.

     The message exchange is terminated when the valid lifetimes of all
     addresses across all IAs have expired, at which time the client may
     use a Solicit message to locate a new DHCP server and send a
     Request for the expired IAs to the new server.

4.4.5.  Updates to Section 18.1.8 of RFC 3315

   Replace Section 18.1.8 of RFC 3315 with the following text:

     Upon the receipt of a valid Reply message in response to a Solicit
     (with a Rapid Commit option), Request, Confirm, Renew, Rebind or
     Information-request message, the client extracts the configuration
     information contained in the Reply.  The client MAY choose to
     report any status code or message from the status code option in
     the Reply message.

     If the client receives a Reply message with a Status Code
     containing UnspecFail, the server is indicating that it was unable
     to process the message due to an unspecified failure condition.  If
     the client retransmits the original message to the same server to
     retry the desired operation, the client MUST limit the rate at
     which it retransmits the message and limit the duration of the time
     during which it retransmits the message.

     When the client receives a Reply message with a Status Code option
     with the value UseMulticast, the client records the receipt of the
     message and sends subsequent messages to the server through the
     interface on which the message was received using multicast.  The
     client resends the original message using multicast.

     When the client receives a NotOnLink status from the server in
     response to a Confirm message, the client performs DHCP server
     solicitation, as described in section 17, and client-initiated
     configuration as described in section 18.  If the client receives



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     any Reply messages that do not indicate a NotOnLink status, the
     client can use the addresses in the IA and ignore any messages that
     indicate a NotOnLink status.

     When the client receives a NotOnLink status from the server in
     response to a Request, the client can either re-issue the Request
     without specifying any addresses or restart the DHCP server
     discovery process (see section 17).

     The client SHOULD perform duplicate address detection [17] on each
     of the received addresses in any IAs, on which it has not performed
     duplicate address detection during processing of any of the
     previous Reply messages from the server.  The client performs the
     duplicate address detection before using the received addresses for
     the traffic.  If any of the addresses are found to be in use on the
     link, the client sends a Decline message to the server for those
     addresses as described in section 18.1.7.

     If the Reply was received in response to a Solicit (with a Rapid
     Commit option), Request, Renew or Rebind message, the client
     updates the information it has recorded about IAs from the IA
     options contained in the Reply message:

     -  Record T1 and T2 times.

     -  Add any new addresses in the IA option to the IA as recorded by
        the client.

     -  Update lifetimes for any addresses in the IA option that the
        client already has recorded in the IA.

     -  Discard any addresses from the IA, as recorded by the client,
        that have a valid lifetime of 0 in the IA Address option.

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

     Management of the specific configuration information is detailed in
     the definition of each option in section 22.

     The client examines the status code in each IA individually.  If
     the client receives a NoAddrsAvail, the client has received no
     usable addresses in the IA.

     If the client finds no usable addresses in any of the IAs, it may
     either try another server (by restarting the DHCP server discovery




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     process) or use the Information-request message to obtain other
     configuration information only.

     The client uses addresses and other information from any IAs that
     do not contain a Status Code option with the NoAddrsAvail code.
     For each IA for which the client receives NoAddrsAvail status code
     the client has the following choices:

     -  The client includes the IA with no addresses in subsequent Renew
        and Rebind messages sent to the server, to request creation of
        the binding for the IA.

     -  Tries another server (by restarting the DHCP server discovery
        process).

     When the client receives a Reply message in response to a Renew or
     Rebind message, for each IA in the original Renew or Rebind
     message, the client:

     -  Sends a Request message if the server responded with the
        NoBinding status code.  The client places only these IA options
        in the Request message for which the server returned NoBinding
        status code in the Reply message.  The client continues to use
        other bindings for which the server did not return an error.

     -  Sends a Renew/Rebind if the IA is not in the Reply message.
        However, in this case, the client MUST limit the rate at which
        it sends subsequent Renew/Rebind messages and limit the duration
        of the time during which it sends the messages.

     -  Otherwise accepts the information in the IA.

     When the client receives a valid Reply message in response to a
     Release message, the client considers the Release event completed,
     regardless of the Status Code option(s) returned by the server.

     When the client receives a valid Reply message in response to a
     Decline message, the client considers the Decline event completed,
     regardless of the Status Code option(s) returned by the server.

4.4.6.  Updates to Section 18.2.3 of RFC 3315

   Replace Section 18.2.3 of RFC 3315 with the following text:

     When the server receives a Renew message via unicast from a client
     to which the server has not sent a unicast option, the server
     discards the Renew message and responds with a Reply message
     containing a Status Code option with the value UseMulticast, a



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     Server Identifier option containing the server's DUID, the Client
     Identifier option from the client message, and no other options.

     For each IA in the Renew message from a client, the server locates
     the client's binding and verifies that the information in the IA
     from the client matches the information stored for that client.

     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, if
     applicable, T1/T2 times.  If the server is unable to extend the
     lifetimes of an address in the IA, the server MAY choose not to
     include the IA Address option for this address.

     The server may choose to change the list of addresses and the
     lifetimes of addresses in IAs that are returned to the client.

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

     For each IA for which the server cannot find a client entry, the
     server has the following choices depending on the server's policy
     and configuration information:

     -  If the server is configured to create new bindings as a result
        of processing Renew messages, the server SHOULD create a binding
        and return the IA with allocated addresses with lifetimes and,
        if applicable, T1/T2 times and other information requested by
        the client.  The server MAY use values in the IA Address option
        (if included) as a hint.

     -  If the server is configured to create new bindings as a result
        of processing Renew messages, but the server will not assign any
        addresses to an IA, the server returns the IA option containing
        a Status Code option with the NoAddrsAvail status code and a
        status message for a user.

     -  If the server does not support creation of new bindings for the
        client sending a Renew message, or if this behavior is disabled
        according to the server's policy or configuration information,
        the server returns the IA option containing a Status code option
        with the NoBinding status code and a status message for a user.

     The server constructs a Reply message by setting the "msg-type"
     field to REPLY, and copying the transaction ID from the Renew
     message into the transaction-id field.





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     The server MUST include a Server Identifier option containing the
     server's DUID and the Client Identifier option from the Renew
     message in the Reply message.

     The server includes other options containing configuration
     information to be returned to the client as described in section
     18.2.

     The T1/T2 times set in each applicable IA option for a Reply MUST
     be the same values across all IAs.  The server MUST determine the
     T1/T2 times across all of the applicable client's bindings in the
     Reply.  This facilitates the client being able to renew all of the
     bindings at the same time.

4.4.7.  Updates to Section 18.2.4 of RFC 3315

   Replace Section 18.2.4 of RFC 3315 with the following text:

      When the server receives a Rebind message that contains an IA
      option from a client, it locates the client's binding and verifies
      that the information in the IA from the client matches the
      information stored for that client.

      If the server finds the addresses in the IA for the client and the
      server determines that the addresses in the IA are appropriate for
      the link to which the client's interface is attached according to
      the server's explicit configuration information, the server SHOULD
      send back the IA to the client with new lifetimes and, if
      applicable, T1/T2 times.  If the server is unable to extend the
      lifetimes of an address in the IA, the server MAY choose not to
      include the IA Address option for this address.

      If the server finds the client entry for the IA and any of the
      addresses are no longer appropriate for the link to which the
      client's interface is attached according to the server's explicit
      configuration information, the server returns the addresses to the
      client with lifetimes of 0.

      If the server cannot find a client entry for the IA, the IA
      contains addresses 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 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 0.  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.



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      Otherwise, for each IA for which the server cannot find a client
      entry, the server has the following choices depending on the
      server's policy and configuration information:

      -  If the server is configured to create new bindings as a result
         of processing Rebind messages (also see the note about the
         Rapid Commit option below), the server SHOULD create a binding
         and return the IA with allocated addresses with lifetimes and,
         if applicable, T1/T2 times and other information requested by
         the client.  The server MAY use values in the IA Address option
         (if included) as a hint.

      -  If the server is configured to create new bindings as a result
         of processing Rebind messages, but the server will not assign
         any addresses to an IA, the server returns the IA option
         containing a Status Code option with the NoAddrsAvail status
         code and a status message for a user.

      -  If the server does not support creation of new bindings for the
         client sending a Rebind message, or if this behavior is
         disabled according to the server's policy or configuration
         information, the server returns the IA option containing a
         Status Code option with the NoBinding status code and a status
         message for a user.

      When the server creates new bindings for the IA it is possible
      that other servers also create bindings as a result of receiving
      the same Rebind message.  This is the same issue as in the
      Discussion under the Rapid Commit option, see section 22.14.
      Therefore, the server SHOULD only create new bindings during
      processing of a Rebind message if the server is configured to
      respond with a Reply message to a Solicit message containing the
      Rapid Commit option.

      The server constructs a Reply message by setting the "msg-type"
      field to REPLY, and copying the transaction ID from the Rebind
      message into the transaction-id field.

      The server MUST include a Server Identifier option containing the
      server's DUID and the Client Identifier option from the Rebind
      message in the Reply message.

      The server includes other options containing configuration
      information to be returned to the client as described in section
      18.2.

      The T1/T2 times set in each applicable IA option for a Reply MUST
      be the same values across all IAs.  The server MUST determine the



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      T1/T2 times across all of the applicable client's bindings in the
      Reply.  This facilitates the client being able to renew all of the
      bindings at the same time.

4.4.8.  Updates to RFC 3633

   Replace Section 12.1:

      Each prefix has valid and preferred lifetimes whose durations are
      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.

   With:

      Each prefix has valid and preferred lifetimes whose durations are
      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 MAY include IA_PD options without any
      prefixes, i.e. without IA Prefix option or with IPv6 prefix field
      of IA Prefix option set to 0, in a Renew or Rebind message to
      obtain bindings it desires but has been unable to obtain.  The
      requesting router MAY set the prefix-length field of the IA Prefix
      option as a hint to the server.

   Replace Section 12.2:

      The delegating router behaves as follows when it cannot find a
      binding for the requesting router's IA_PD:

   With:

      For the Renew or Rebind, if the IA_PD contains no prefixes, i.e.
      contains no IA Prefix option or the IPv6 prefix field in the IA
      Prefix option is set to 0, the delegating router SHOULD assign
      prefixes to the IA_PD according to the delegating router's
      explicit configuration information.  In this case, when the server
      assigns new prefixes to the IA_PD, the server MAY use the value in
      the prefix-length field of the IA Prefix option as a hint for the
      length of the prefixes being assigned.

      The delegating router behaves as follows when it cannot find a
      binding for the requesting router's IA_PD containing prefixes:






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4.5.  Confirm Message

   The Confirm message, as described in [RFC3315], is specific to
   address assignment.  It allows a server without a binding to reply to
   the message, under the assumption that the server only needs
   knowledge about the prefix(es) on the link, to inform the client that
   the address is likely valid or not.  This message is sent when e.g.
   the client has moved and needs to validate its addresses.  Not all
   bindings can be validated by servers and the Confirm message provides
   for this by specifying that a server that is unable to determine the
   on-link status MUST NOT send a Reply.

   Note: Confirm has a specific meaning and does not overload Renew/
   Rebind.  It also is lower processing cost as the server does NOT need
   to extend lease times or otherwise send back other configuration
   options.

   The Confirm message is used by the client to verify that it has not
   moved to a different link.  For IAs with addresses, the mechanism
   used to verify if a client has moved or not, is by matching the
   link's on-link prefix(es) (typically a /64) against the prefix-length
   first bits of the addresses provided by the client in the IA_NA or
   IA_TA IA-types.  As a consequence Confirm can only be used when the
   client has an IA with address(es) (IA_NA or IA_TA).

   A client MUST have a binding including an IA with addresses to use
   the Confirm message.  A client with IAs with addresses as well as
   other IA-types MAY, depending on the IA-type, use the Confirm message
   to detect if the client has moved to a different link.  A client that
   does not have a binding with an IA with addresses MUST use the Rebind
   message instead.

   IA_PD requires verification that the server has the binding for the
   IAs.  In that case a client MUST use the Rebind message in place of
   the Confirm message and it MUST include all of its bindings, even
   address IAs.

   Note that Section 18.1.2 of RFC 3315 states that a client MUST
   initiate a Confirm when it may have moved to a new link.  This is
   relaxed to a SHOULD as a client may have determined whether it has or
   has not moved using other techniques, such as described in [RFC6059].
   And, as stated above, a client with delegated prefixes, MUST send a
   Rebind instead of a Confirm.








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4.6.  Decline Should Not Necessarily Trigger a Release

   Some client implementations have been found to send a Release message
   for other bindings they may have received after they determine a
   conflict and have correctly sent a Decline message for the
   conflicting address(es).

   It is recommended that a client SHOULD NOT send a Release message for
   other bindings it may have received just because it sent a Decline
   message.  The client should retain the non-conflicting bindings.

4.7.  Multiple Provisioning Domains

   This document has assumed that all DHCP servers on a network are in a
   single provisioning domain and thus should be "equal" in the service
   that they offer.  This was also assumed by [RFC3315] and [RFC3633].

   One could envision a network where the DHCP servers are in multiple
   provisioning domains, and it may be desirable to have the DHCP client
   obtain different IA types from different provisioning domains.  How a
   client detects the multiple provisioning domains and how it would
   interact with the multiple servers in these different domains is
   outside the scope of this document.

5.  IANA Considerations

   This specification does not require any IANA actions.

6.  Security Considerations

   There are no new security considerations pertaining to this document.

7.  Acknowledgements

   Thanks to many people that contributed to identify the stateful
   issues addressed by this document and for reviewing drafts of the
   document, including Ralph Droms, John Brzozowski, Ted Lemon, Hemant
   Singh, Wes Beebee, Gaurau Halwasia, Bud Millword, Tim Winters, Rob
   Shakir, Jinmei Tatuya, Andrew Yourtchenko, and Fred Templin.

8.  References

8.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.





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   [RFC3315]  Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C.,
              and M. Carney, "Dynamic Host Configuration Protocol for
              IPv6 (DHCPv6)", RFC 3315, July 2003.

   [RFC3633]  Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic
              Host Configuration Protocol (DHCP) version 6", RFC 3633,
              December 2003.

   [RFC7083]  Droms, R., "Modification to Default Values of SOL_MAX_RT
              and INF_MAX_RT", RFC 7083, November 2013.

8.2.  Informative References

   [I-D.dhcwg-dhc-rfc3315bis]
              Mrugalski, T., Siodelski, M., Volz, B., Yourtchenko, A.,
              Richardson, M., Jiang, S., and T. Lemon, "Dynamic Host
              Configuration Protocol for IPv6 (DHCPv6) bis", draft-
              dhcwg-dhc-rfc3315bis-03 (work in progress), October 2014.

   [RFC4941]  Narten, T., Draves, R., and S. Krishnan, "Privacy
              Extensions for Stateless Address Autoconfiguration in
              IPv6", RFC 4941, September 2007.

   [RFC6059]  Krishnan, S. and G. Daley, "Simple Procedures for
              Detecting Network Attachment in IPv6", RFC 6059, November
              2010.

   [RFC7084]  Singh, H., Beebee, W., Donley, C., and B. Stark, "Basic
              Requirements for IPv6 Customer Edge Routers", RFC 7084,
              November 2013.

   [RFC7227]  Hankins, D., Mrugalski, T., Siodelski, M., Jiang, S., and
              S. Krishnan, "Guidelines for Creating New DHCPv6 Options",
              BCP 187, RFC 7227, May 2014.

Authors' Addresses

   Ole Troan
   Cisco Systems, Inc.
   Philip Pedersens vei 20
   N-1324 Lysaker
   Norway

   Email: ot@cisco.com







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   Bernie Volz
   Cisco Systems, Inc.
   1414 Massachusetts Ave
   Boxborough, MA  01719
   USA

   Email: volz@cisco.com


   Marcin Siodelski
   ISC
   950 Charter Street
   Redwood City, CA  94063
   USA

   Email: msiodelski@gmail.com



































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