[Docs] [txt|pdf|xml|html] [Tracker] [WG] [Email] [Diff1] [Diff2] [Nits]

Versions: (draft-fsc-softwire-dhcp4o6-saddr-opt) 00 01 02 03

DHCWG                                                          I. Farrer
Internet-Draft                                       Deutsche Telekom AG
Updates: 7598 (if approved)                                       Q. Sun
Intended status: Standards Track                                  Y. Cui
Expires: September 28, 2018                                       L. Sun
                                                     Tsinghua University
                                                          March 27, 2018


             Softwire Provisioning using DHCPv4 Over DHCPv6
                  draft-ietf-dhc-dhcp4o6-saddr-opt-03

Abstract

   DHCPv4 over DHCPv6 is a mechanism for dynamically configuring IPv4
   over an IPv6-only network.  For DHCPv4 over DHCPv6 to function with
   some IPv4-over-IPv6 softwire mechanisms and deployment scenarios, the
   operator needs to know the IPv6 address that the client will use as
   the source of IPv4-in-IPv6 softwire tunnel.  This address, in
   conjunction with the client's IPv4 address and (in some deployments),
   the Port Set ID are used to create a binding table entry in the
   operator's softwire tunnel concentrator.  This memo defines a DHCPv6
   option to convey IPv6 parameters for establishing the softwire tunnel
   and a DHCPv4 option (to be used only with DHCP 4o6) to communicate
   the source tunnel IPv6 address between the DHCP 4o6 client and
   server.  It is designed to work in conjunction with the IPv4 address
   allocation process.  This document updates "DHCPv6 Options for
   Configuration of Softwire Address and Port-Mapped Clients" to allow
   the DHCPv6 option OPTION_S46_BR (90) to appear outside of DHCPv6
   softwire container options.

   This document updates RFC7598, allowing OPTION_S46_BR (90) to be
   enumerated in the DHCPv6 client's ORO request and appear directly
   within subsequent messages sent by the DHCPv6 server.

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 https://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




Farrer, et al.         Expires September 28, 2018               [Page 1]


Internet-Draft      Softwire Provising with DHCP 4o6          March 2018


   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 September 28, 2018.

Copyright Notice

   Copyright (c) 2018 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
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   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  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Applicability . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Requirements Language . . . . . . . . . . . . . . . . . . . .   4
   4.  Solution Overview . . . . . . . . . . . . . . . . . . . . . .   4
     4.1.  Updating RFC7598 to Permit the Reuse of OPTION_S46_BR(90)   4
   5.  DHCP 4o6 IPv6/IPv4 Binding Message Flow . . . . . . . . . . .   5
   6.  DHCP Options  . . . . . . . . . . . . . . . . . . . . . . . .   7
     6.1.  DHCPv6 Softwire Source Binding Prefix Hint Option . . . .   7
     6.2.  DHCPv4 over DHCPv6 Softwire Source Address Option . . . .   7
   7.  Client Behavior . . . . . . . . . . . . . . . . . . . . . . .   8
     7.1.  Client Initialization . . . . . . . . . . . . . . . . . .   8
     7.2.  Renewing or Rebinding the IPv4 Address Lease and
           Softwire Source Address . . . . . . . . . . . . . . . . .   9
       7.2.1.  Changing the Bound IPv6 Softwire Source Address . . .  10
     7.3.  Releasing the IPv4 Address Lease and Softwire
           Source Address  . . . . . . . . . . . . . . . . . . . . .  10
     7.4.  OPTION_S46_BIND_IPV6_PREFIX Validation Behavior . . . . .  10
     7.5.  Client and Server Softwire Source Address Mismatch  . . .  11
     7.6.  Use With Dynamic, Shared IPv4 Addresses . . . . . . . . .  11
   8.  Server Behavior . . . . . . . . . . . . . . . . . . . . . . .  11
     8.1.  Changing the Bound IPv6 Source Address  . . . . . . . . .  11
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .  12
   10. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  12
   11. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  12
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . .  13
     12.1.  Normative References . . . . . . . . . . . . . . . . . .  13



Farrer, et al.         Expires September 28, 2018               [Page 2]


Internet-Draft      Softwire Provising with DHCP 4o6          March 2018


     12.2.  Informative References . . . . . . . . . . . . . . . . .  13
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  13

1.  Introduction

   Deterministic IPv4-over-IPv6 transition technologies require that
   elements are pre-configured with binding rules for routing traffic to
   clients.  This places a constraint on the choice of address used as
   the client's softwire source address: it must use a pre-determined
   prefix which is usually configured on the home gateway device.
   [RFC7597] describes a DHCPv6 based mechanism for provisioning such
   deterministic softwires.

   A dynamic provisioning model, such as using DHCPv4 over DHCPv6
   [RFC7341] (DHCP 4o6) allows much more flexibility in the location of
   the IPv4-over-IPv6 softwire source address.  In this model, the IPv6
   address is dynamically communicated back to the service provider
   allowing the corresponding softwire configuration to be created in
   the border router (BR).

   The DHCP 4o6 client and softwire client could be run on end devices
   attached to any routable IPv6 prefix allocated to an end-user,
   located anywhere within an arbitrary home network topology.  Dynamic
   allocation also helps to optimize IPv4 resource usage as only clients
   which are actively renewing their IPv4 lease hold on to the address.

   This document describes a mechanism for dynamically provisioning
   softwires created using DHCP 4o6, including provisioning the client
   with the address of the softwire border router (BR) and informing the
   service provider of client's binding between the dynamically
   allocated IPv4 address and Port Set ID and the IPv6 address that the
   softwire Initiator will use for accessing IPv4-over-IPv6 services.

   The mechanism operates alongside the DHCP 4o6 message flows to
   communicate the binding information over the IPv6-only network.  The
   DHCP 4o6 server provides a single point in the network which holds
   the current client binding information.  The service provider can
   then use this binding information to provision other functional
   elements, such as the BR(s).

2.  Applicability

   The mechanism described in this document is only suitable for use for
   provisioning softwire clients via DHCP 4o6.  The options described
   here are only applicable within the DHCP 4o6 message exchange
   process.  Current softwire technologies suitable for extending to
   incorporate DHCP 4o6 with dynamic IPv4 address leasing include
   [RFC7597] and [RFC7596].



Farrer, et al.         Expires September 28, 2018               [Page 3]


Internet-Draft      Softwire Provising with DHCP 4o6          March 2018


3.  Requirements Language

   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 RFC 2119 [RFC2119].

4.  Solution Overview

   In order to provision a softwire, both IPv6 and IPv4 configuration
   needs to be passed to the client.  To map this to the DHCP 4o6
   configuration process, the IPv6 configuration is carried in DHCPv6
   options carried inside the DHCPv6 message DHCPV4-RESPONSE (21) sent
   by the server.  OPTION_S46_BR (90) is used to provision the remote
   IPv6 address for the softwire (see Section 4.1 below).
   OPTION_S46_BIND_IPV6_PREFIX (TBD1), is optionally sent by the DHCP
   4o6 server to indicate to the client a preferred IPv6 prefix for
   binding the received IPv4 configuration and sourcing tunnel traffic.
   This may be necessary if there are multiple IPv6 prefixes in use in
   the customer network (e.g.  ULAs), or if the specific IPv4-over-IPv6
   transition mechanism requires the use of a particular prefix for any
   reason.

   IPv4 configuration is carried in DHCPv4 messages (inside the DHCP 4o6
   option OPTION_DHCPV4_MSG (87)) using the mechanism described in
   [RFC7341].

   In order for the client to communicate the softwire source address, a
   new DHCPv4 option OPTION_DHCP4O6_S46_SADDR (TBD2) is defined in this
   document.  This is included in DHCPREQUEST messages sent by the
   client and is stored by the server for the lifetime of the IPv4
   address lease.

4.1.  Updating RFC7598 to Permit the Reuse of OPTION_S46_BR(90)

   Section 4.2 of [RFC7598] defines option OPTION_S46_BR(90) for
   communicating remote softwire border relay (BR)'s' IPv6 address(es)
   to a client, but mandates that the option can only be used when
   encapsulated within one of the softwire container options:
   OPTION_S46_CONT_MAPE (94) or OPTION_S46_CONT_LW(96).  From Section 3
   of [RFC7598]:

      "Softwire46 DHCPv6 clients that receive provisioning options that
      are not encapsulated in container options MUST silently ignore
      these options."

   This document updates [RFC7598], removing this restriction for
   OPTION_S46_BR (90), allowing it to be enumerated in the client's ORO




Farrer, et al.         Expires September 28, 2018               [Page 4]


Internet-Draft      Softwire Provising with DHCP 4o6          March 2018


   request and appear directly within subsequent messages sent by the
   DHCPv6 server.

5.  DHCP 4o6 IPv6/IPv4 Binding Message Flow

   The following diagram shows the relevant extensions to the successful
   DHCP 4o6 IPv4 allocation client/server message flow for the softwire
   source address function.  The full process, including error handling
   is described in Section 7.

   In each step, the DHCPv6 portion of the message and any relevant
   option is shown above the arrow.  The DHCP 4o6 content of the message
   and its relevant options are below the arrow.  All the DHCPv4
   messages are encapsulated in DHCPV4-QUERY (20) or DHCPV4-RESPONSE
   (21) messages.  Where relevant, the necessary options and their
   contents are shown.



































Farrer, et al.         Expires September 28, 2018               [Page 5]


Internet-Draft      Softwire Provising with DHCP 4o6          March 2018


        DHCP 4o6                                              DHCP 4o6
         Client                                                Server
           |                                                      |
           |       DHCPv6 - DHCPV4-QUERY message containing       |
           |           OPTION_ORO(6) listing (90, TBD1)           |
    Step 1 |----------------------------------------------------->|
           |            DHCPv4 - DHCPDISCOVER message             |
           |                                                      |
           |                                                      |
           |     DHCPv6 - DHCPV4-RESPONSE message containing      |
           | OPTION_S46_BR(90), OPTION_S46_BIND_IPV6_PREFIX(TDB1) |
           |     (bind-ipv6-prefix with service provider's        |
           |                  preferred prefix)                   |
    Step 2 |<-----------------------------------------------------|
           |              DHCPv4 - DHCPOFFER message              |
           |                                                      |
           |                                                      |
           |             DHCPv6 - DHCPV4-QUERY message            |
    Step 3 |----------------------------------------------------->|
           |       DHCPv4 -  DHCPREQUEST message containing       |
           |  OPTION_DHCP4O6_S46_SADDR (softwire-ipv6-src-address |
           |   with client's bound IPv6 softwire source address)  |
           |                                                      |
           |                                                      |
           |           DHCPv6 - DHCPV4-RESPONSE message           |
    Step 4 |<-----------------------------------------------------|
           |          DHCPv4 - DHCPACK message containing         |
           |  OPTION_DHCP4O6_S46_SADDR (softwire-ipv6-src-address |
           |   with client's bound IPv6 softwire source address)  |
           |                                                      |

                 Figure 1: IPv6/IPv4 Binding Message Flow

   Step 1  The client constructs a DHCPv6 'DHCPV4-QUERY(20)' message.
           This message contains two options: DHCPv6 OPTION_ORO (6) and
           OPTION_DHCPV4_MSG (87).  OPTION_ORO lists '90'
           (OPTION_S46_BR) and 'TBD1' (OPTION_S46_BIND_IPV6_PREFIX).
           OPTION_DHCPV4_MSG contains a DHCPv4 DHCPDISCOVER message.

   Step 2  The server responds with a DHCPv6 'DHCPV4-RESPONSE (21)'
           message.  This message contains OPTION_S46_BR (90) containing
           the IPv6 address of the BR for the client's softwire
           configuration.  The message may also, optionally contain
           OPTION_S46_BIND_IPV6_PREFIX (TBD1).  OPTION_DHCPV4_MSG
           contains a DHCPv4 DHCPOFFER message.

   Step 3  The client sends with a DHCPv6 'DHCPV4-QUERY(20)' message
           containing a DHCPv4 DHCPREQUEST message with



Farrer, et al.         Expires September 28, 2018               [Page 6]


Internet-Draft      Softwire Provising with DHCP 4o6          March 2018


           OPTION_DHCP4O6_S46_SADDR (TBD2) with the IPv6 address which
           the client will use as its softwire source address.

   Step 4  The server sends a DHCPv6 'DHCPV4-RESPONSE(21)' message.
           OPTION_DHCPV4_MSG contains a DHCPv4 DHCPACK message.
           OPTION_DHCP4O6_S46_SADDR with the client's softwire source
           address is included.

6.  DHCP Options

6.1.  DHCPv6 Softwire Source Binding Prefix Hint Option

   The format of DHCPv6 Source Binding Prefix hint option is as follows:

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |  OPTION_S46_BIND_IPV6_PREFIX  |         option-length         |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |bindprefix6-len|                                               |
     +-+-+-+-+-+-+-+-+             bind-ipv6-prefix                  .
     .                            (variable length)                  .
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                   Format of OPTION_S46_BIND_IPV6_PREFIX

   o  option-code: OPTION_S46_BIND_IPV6_PREFIX (TBD1)
   o  option-length: 1 + length of bind-ipv6-prefix, specified in bytes.
   o  bindprefix6-len: 8-bit field expressing the bit mask length of the
      IPv6 prefix specified in bind-ipv6-prefix.  Valid values are 0 to
      128.
   o  bind-ipv6-prefix: The IPv6 prefix indicating the preferred prefix
      for the client to bind the received IPv4 configuration to.  The
      length is (bindprefix6-len + 7) / 8.  The field is padded on the
      right with zero bits up to the next octet boundary when bind-
      ipv6-prefix is not evenly divisible by 8.

   OPTION_S46_BIND_IPV6_PREFIX is a singleton.  Servers MUST NOT send
   more than one instance of the OPTION_S46_BIND_IPV6_PREFIX option.

6.2.  DHCPv4 over DHCPv6 Softwire Source Address Option

   The format of DHCPv4 over DHCPv6 softwire source address option is as
   follows:







Farrer, et al.         Expires September 28, 2018               [Page 7]


Internet-Draft      Softwire Provising with DHCP 4o6          March 2018


              0                             1
              0  1  2  3  4  5  6  7  8  9  0  1  2  3  4  5
             +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
             |   option-code (TBD)   |     option-length     |
             +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
             +           softwire-ipv6-src-address           +
             .                  (128 bits)                   .
             +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+

                    Format of OPTION_DHCP4O6_S46_SADDR

   o  option-code: OPTION_DHCP4O6_S46_SADDR (TBD2)
   o  option-length: 16.
   o  softwire-ipv6-src-address: 16 bytes long; The IPv6 address that is
      associated (either being requested for binding or currently bound)
      with the client's IPv4 configuration.

   NB - The function of OPTION_DHCP4O6_S46_SADDR may seem similar to the
   DHCPv4 message's 'chaddr' field, or the Client Identifier (61) option
   in that it provides a lower-layer address which is unique that the
   server can use for identifying the client.  However, as both of these
   are required to remain constant throughout the address lease
   lifetime, they cannot be used with the mechanism described in this
   document.  This is because the client may only be able to construct
   the IPv6 address to use as the source address after it has received
   the first DHCPV4-RESPONSE message from the server containing
   OPTION_S46_BIND_IPV6_PREFIX.

7.  Client Behavior

   A client requiring dynamic softwire configuration first enables DHCP
   4o6 configuration using the method described in Section 5.  of
   [RFC7341].  If OPTION_DHCP4_O_DHCP6_SERVER is received in the
   corresponding REPLY message, the client MAY continue with the
   configuration process described below.

   It is also a prerequisite that the client has already learned a
   suitable IPv6 prefix to use for its local softwire endpoint using
   DHCPv6, RA/PIO or another mechanism.

7.1.  Client Initialization

   When constructing the initial DHCP 4o6 DHCPDISCOVER message, the
   client includes a DHCPv6 OPTION_ORO (6) within the options field of
   the DHCP-QUERY message.  OPTION_ORO contains the option codes for
   OPTION_S46_BR (90) and OPTION_S46_BIND_IPV6_PREFIX (TBD1).





Farrer, et al.         Expires September 28, 2018               [Page 8]


Internet-Draft      Softwire Provising with DHCP 4o6          March 2018


   On receipt of the DHCP 4o6 server's reply (a DHCPV4-RESPONSE
   containing a DHCPOFFER message), the client checks the contents of
   the DHCPv4-RESPONSE for the presence of a valid OPTION_S46_BR option.
   If this option is not present, or does not contain at least one valid
   IPv6 address for a BR, then the client MUST discard the message, as
   without the address of the BR the client cannot configure the
   softwire and so has no interface to request IPv4 configuration for.

   The DHCPV4-RESPONSE message may also include
   OPTION_S46_BIND_IPV6_PREFIX, which is used by the operator to
   indicate a preferred prefix that the client should use to bind IPv4
   configuration to.  If received, the client first checks the option
   according to Section 7.4.  If valid, the client uses this prefix as
   the 'IPv6 binding prefix' and follows to the process described in
   Section 5.1 of [RFC7596] in order to select an active IPv6 prefix to
   construct the softwire.  If no match is found, or the client doesn't
   receive OPTION_S46_BIND_IPV6_PREFIX the client MAY select any valid
   IPv6 prefix (of a suitable scope) to use as the tunnel source.

   Once the client has selected a suitable prefix, it MAY use either an
   existing IPv6 address that is already configured on an interface, or
   create a new address specifically for use as the softwire source
   address (e.g. using an Interface Identifier constructed as per
   Section 6. of [RFC7597]).  If a new address is being created, the
   client MUST complete configuration of the new address, performing
   duplicate address detection (if required) before proceeding.

   The client then constructs a DHCPV4-QUERY message containing a DHCPv4
   DHCPREQUEST message.  OPTION_DHCP4O6_S46_SADDR is included in the
   options field of the DHCPREQUEST message with the IPv6 address of its
   softwire source address in the softwire-ipv6-src-address field.

   When the client receives a DHCPv4 DHCPACK message from the server, it
   checks the IPv6 address in OPTION_DHCP4O6_S46_SADDR against its
   active softwire source address.  If they match, the allocation
   process has concluded.  If there is a discrepancy then the process
   described in Section 7.5 is followed.

   If the client receives a DHCPv4 DHCPNAK message from the server, then
   the configuration process has been unsuccessful.  The client then
   restarts the process from Step 1 of Figure 1.

7.2.  Renewing or Rebinding the IPv4 Address Lease and Softwire Source
      Address

   Whenever the client attempts to extend the lease time of the IPv4
   address, OPTION_DHCP4O6_S46_SADDR with the IPv6 address of its




Farrer, et al.         Expires September 28, 2018               [Page 9]


Internet-Draft      Softwire Provising with DHCP 4o6          March 2018


   softwire source address in the softwire-ipv6-src-address field MUST
   be included in the DHCPREQUEST message.

7.2.1.  Changing the Bound IPv6 Softwire Source Address

   Across the lifetime of the leased IPv4 address, it is possible that
   the client's IPv6 will change.  E.g. if there is a flash IPv6 re-
   numbering event.

   In this situation, the client MUST inform the server of the new
   address.  This is done by sending a DHCPREQUEST message containing
   OPTION_DHCP4O6_S46_SADDR with the new IPv6 source address.

   When the client receives a DHCPv4 DHCPACK message from the server, it
   checks the IPv6 address in OPTION_DHCP4O6_S46_SADDR against its
   active softwire source address.  If they match, the allocation
   process has concluded.  If there is a discrepancy then the process
   described in Section 7.5 is followed.

   If the client receives a DHCPv4 DHCPNAK message in repsonse from the
   server, then the change of the bound IPv6 Softwire source address has
   been unsuccessful.  In this case, the client MUST stop using the new
   IPv6 source address.  The client then restarts the process from Step
   1 of Figure 1.

7.3.  Releasing the IPv4 Address Lease and Softwire Source Address

   When the client no longer requires the IPv4 resource, it sends a
   DHCPv4 DHCPRELEASE message to the server.  As the options field is
   unused in this message type, OPTION_DHCP4O6_S46_SADDR is not
   included.

7.4.  OPTION_S46_BIND_IPV6_PREFIX Validation Behavior

   On receipt of the OPTION_S46_BIND_IPV6_PREFIX option, the client
   makes the following validation checks:

   o  The received bindprefix6-len value is not larger than 128.
   o  The received bindprefix6-len value is not larger than the number
      of bytes sent in the bind-ipv6-prefix field. (e.g. the
      bindprefix6-len is 128 but the bind-ipv6-prefix has only 8 bytes).

   For either of these cases the receiver MAY either discard the option
   and proceed to attempt configuration as if the option had not been
   received, or attempt to use the received values for the longest
   prefix match anyway.





Farrer, et al.         Expires September 28, 2018              [Page 10]


Internet-Draft      Softwire Provising with DHCP 4o6          March 2018


   The receiver MUST only use bits from the bind-ipv6-prefix field up to
   the value specified in the bindprefix6-len when performing the
   longest prefix match. bind-ipv6-prefix bits beyond this value MUST be
   ignored.

7.5.  Client and Server Softwire Source Address Mismatch

   If the client receives a DHCPACK message with an
   OPTION_DHCP4O6_S46_SADDR containing an IPv6 address which differs
   from its active softwire source address, the client MAY either:

   o  Wait for a randomised time interval and then resend a DHCPREQUEST
      message with the correct softwire source address, OR
   o  Send a DHCPRELEASE message and re-start the process described in
      Section 7.

7.6.  Use With Dynamic, Shared IPv4 Addresses

   [RFC7618]describes a mechanism for using DHCPv4 to distribute
   dynamic, shared IPv4 addresses to clients.  The mechanism described
   in this document is compatible with IPv4 address sharing, and can be
   enabled by following the process described in Section 6 of [RFC7618].

8.  Server Behavior

   Beyond the normal DHCP 4o6 functionality defined in [RFC7341], the
   server MUST also store the IPv6 softwire source address of the client
   in the leasing address database, alongside the IPv4 address and
   client identifier.  An OPTION_DHCP4O6_S46_SADDR containing the bound
   softwire source address MUST be sent in every DHCPACK message sent by
   the server.

   The binding entry between the client's IPv6 softwire source address
   and the leased IPv4 address is valid as long as the IPv4 lease
   remains valid.

8.1.  Changing the Bound IPv6 Source Address

   In the event that the server receives a DHCPREQUEST message for an
   active IPv4 lease containing a OPTION_DHCP4O6_S46_SADDR with an IPv6
   address which differs from the address which is currently stored, the
   server updates the stored softwire source address with the new
   address supplied by the client, and sends a DHCPACK message
   containing the updated softwire source address in
   OPTION_DHCP4O6_S46_SADDR.

   The server MAY implement a policy enforcing a minimum time interval
   between a client updating its softwire source IPv6 address.  If a



Farrer, et al.         Expires September 28, 2018              [Page 11]


Internet-Draft      Softwire Provising with DHCP 4o6          March 2018


   client attempts to update the softwire source IPv6 address before the
   minimum time has expired, the server can either silently drop the
   client's message or send back a DHCPACK message containing the
   exisiting IPv6 address binding in OPTION_DHCP4O6_S46_SADDR.

9.  Security Considerations

   Security considerations which are applicable to [RFC7341] are also
   applicable here.

10.  IANA Considerations

   IANA is requested to assign the OPTION_DHCP4O6_S46_SADDR option code
   from the "BOOTP Vendor Extensions and DHCP Options" registry
   maintained at http://www.iana.org/assignments/bootp-dhcp-parameters.

   IANA is requested to assign the OPTION_S46_BIND_IPV6_PREFIX option
   code from the DHCPv6 "Option Codes" registry maintained at
   http://www.iana.org/assignments/dhcpv6-parameters.

   IANA is requested to update the entry for DHCPv6 Option S46_BR (90)
   in the table at https://www.iana.org/assignments/dhcpv6-parameters as
   follows:

   Old entry:

   |    90 | S46_BR                  | No                  | No        |

   New entry:

   |    90 | S46_BR                  | Yes                 | No        |

   IANA is also requested to make a new entry for
   OPTION_S46_BIND_IPV6_PREFIX TBD1) in the table at
   https://www.iana.org/assignments/dhcpv6-parameters:

   |  TBD1 |OPTION_S46_BIND_IPV6_PREFIX| Yes               | Yes       |

11.  Acknowledgements

   The authors would like to thank Ted Lemon, Lishan Li, Tatuya Jinmei,
   Jonas Gorski and Razvan Becheriu for their contributions and
   comments.








Farrer, et al.         Expires September 28, 2018              [Page 12]


Internet-Draft      Softwire Provising with DHCP 4o6          March 2018


12.  References

12.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC7341]  Sun, Q., Cui, Y., Siodelski, M., Krishnan, S., and I.
              Farrer, "DHCPv4-over-DHCPv6 (DHCP 4o6) Transport",
              RFC 7341, DOI 10.17487/RFC7341, August 2014,
              <https://www.rfc-editor.org/info/rfc7341>.

12.2.  Informative References

   [RFC7596]  Cui, Y., Sun, Q., Boucadair, M., Tsou, T., Lee, Y., and I.
              Farrer, "Lightweight 4over6: An Extension to the Dual-
              Stack Lite Architecture", RFC 7596, DOI 10.17487/RFC7596,
              July 2015, <https://www.rfc-editor.org/info/rfc7596>.

   [RFC7597]  Troan, O., Ed., Dec, W., Li, X., Bao, C., Matsushima, S.,
              Murakami, T., and T. Taylor, Ed., "Mapping of Address and
              Port with Encapsulation (MAP-E)", RFC 7597,
              DOI 10.17487/RFC7597, July 2015,
              <https://www.rfc-editor.org/info/rfc7597>.

   [RFC7598]  Mrugalski, T., Troan, O., Farrer, I., Perreault, S., Dec,
              W., Bao, C., Yeh, L., and X. Deng, "DHCPv6 Options for
              Configuration of Softwire Address and Port-Mapped
              Clients", RFC 7598, DOI 10.17487/RFC7598, July 2015,
              <https://www.rfc-editor.org/info/rfc7598>.

   [RFC7618]  Cui, Y., Sun, Q., Farrer, I., Lee, Y., Sun, Q., and M.
              Boucadair, "Dynamic Allocation of Shared IPv4 Addresses",
              RFC 7618, DOI 10.17487/RFC7618, August 2015,
              <https://www.rfc-editor.org/info/rfc7618>.

Authors' Addresses

   Ian Farrer
   Deutsche Telekom AG
   CTO-ATI, Landgrabenweg 151
   Bonn, NRW  53227
   Germany

   Email: ian.farrer@telekom.de




Farrer, et al.         Expires September 28, 2018              [Page 13]


Internet-Draft      Softwire Provising with DHCP 4o6          March 2018


   Qi Sun
   Tsinghua University
   Beijing  100084
   P.R. China

   Phone: +86-10-6278-5822
   Email: sunqi.csnet.thu@gmail.com


   Yong Cui
   Tsinghua University
   Beijing  100084
   P.R. China

   Phone: +86-10-6260-3059
   Email: yong@csnet1.cs.tsinghua.edu.cn


   Linhui Sun
   Tsinghua University
   Beijing  100084
   P.R. China

   Phone: +86-10-6278-5822
   Email: lh.sunlinh@gmail.com


























Farrer, et al.         Expires September 28, 2018              [Page 14]


Html markup produced by rfcmarkup 1.126, available from https://tools.ietf.org/tools/rfcmarkup/