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Versions: 00 01 02                                                      
Network Working Group                                             C. Liu
Internet-Draft                                                    Q. Sun
Intended status: Informational                                     J. Wu
Expires: September 22, 2016                          Tsinghua University
                                                               I. Farrer
                                                     Deutsche Telekom AG
                                                          March 21, 2016

            Dynamic IPv4 Provisioning for Lightweight 4over6


   Lightweight 4over6 [RFC7596] is an IPv4 over IPv6 hub-and-spoke
   mechanism that provides overlay IPv4 services in an IPv6-only access
   network.  It uses a deterministic, DHCPv6 based method for the
   provisioning of IPv4 addresses and port sets to customer CE devices.
   This document describes how existing specifications can be used for
   the dynamic IPv4 provisioning of Lightweight 4over6, based on DHCPv4
   over DHCPv6 [RFC7341].

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 September 22, 2016.

Copyright Notice

   Copyright (c) 2016 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.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Architecture Overview . . . . . . . . . . . . . . . . . . . .   4
   4.  Lightweight4over6 Dynamic Provisioning Process  . . . . . . .   5
     4.1.  Client IPv6 Addressing  . . . . . . . . . . . . . . . . .   5
     4.2.  DHCPv6 Configuration  . . . . . . . . . . . . . . . . . .   5
     4.3.  DHCPv4 over DHCPv6 Function . . . . . . . . . . . . . . .   5
     4.4.  lwAFTR Binding Table Maintenance  . . . . . . . . . . . .   5
       4.4.1.  Co-located lwAFTR/DHCP4o6 Binding Table Maintenance .   6
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
     5.1.  Data Retention Requirements . . . . . . . . . . . . . . .   6
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   7
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .   7
     7.2.  Informative References  . . . . . . . . . . . . . . . . .   7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   8

1.  Introduction

   Lightweight 4over6 [RFC7596] provides IPv4 access over an IPv6
   network in hub-and-spoke softwire architecture.  In Lightweight
   4over6, each Lightweight B4 (lwB4) is assigned a full, or shared
   (port-restricted) IPv4 address to be used for IPv4 communication.
   Provisioning the lwB4 with its IPv4 address, port set and other
   parameters necessary for building the softwire is the core function
   of the Lightweight 4over6 control plane.

   [RFC7596] describes the use of DHCPv6 for deterministic IPv4
   provisioning.  The IPv4 address, port set ID (PSID) and address of
   the lwAFTR are carried in DHCPv6 options defined in [RFC7598].

   However, the deterministic provisioning of the IPv4 parameters
   imposes restrictions on the deployment:

   o  The IPv4 address' life time is bound to the client's IPv6 tunnel
      endpoint life time

   o  The tunnel must be initiated from a fixed and predictable /64
      prefix in the home network topology

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   o  The IPv4 address and PSID need to be embedded into the IID of the
      clients' /128 IPv6 address

   o  IPv4 address resources are permanently reserved for a client
      whether it is active or not.  This results in less efficient
      public IPv4 address usage

   This document describes the deployment of Lightweight 4over6 using
   DHCPv4 over DHCPv6 for dynamic IPv4 address provisioning.  The main
   advantages of using a dynamic provisioning model over a deterministic
   model are as follows:

   o  No inherent restrictions on the IPv6 source address within the
      customer internal network that the client uses for sourcing its
      tunneled traffic

   o  The lifetimes of IPv6 and IPv4 addresses are decoupled, allowing
      for more flexibility in the service provider's addressing policy

   o  Inactive clients' addresses can be released/reclaimed for
      allocation to active clients, so more efficient address usage is

   Since DHCPv4 over IPv4 cannot be used natively in a single stack IPv6
   network, DHCPv4 over DHCPv6 (DHCP4o6) [RFC7341] allows DHCPv4
   functionality to be trasported over a pure in IPv6 network by placing
   DHCPv4 messages within DHCPv6 messages.

   [I-D.fsc-softwire-dhcp4o6-saddr-opt] defines a DHCP4o6 based
   mechanism for the lwB4 to inform the server of its IPv6 tunnel source

   The architecture which is described in this document can be
   implemented with or without the sharing of IPv4 addresses between
   multiple clients.  If IPv4 address sharing is required, then
   [RFC7618] describes the changes necessary extensions to the DHCPv4
   server and client provisioning for the allocation and lease
   management of shared IPv4 addresses.

2.  Terminology

   Terminology defined in [RFC7341] and [RFC7596] is used extensively
   throughout this document.

   Unless stated otherwise, the term "lwB4" should be understood to mean
   a stateful lwB4 using DHCP4o6 for dynamic IPv4 provisioning.

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3.  Architecture Overview

   There are four functional elements which make up the architecture.
   Although these are shown as being seperate entities, it is possibile
   that one or more of the operator side functions might be performed by
   a single device.

                 ________     __________
                |        |   |          |
                | DHCPv6 |   | DHCP4o6 |
                | Server |   |  Server  |
                |________|   |__________|
                    ^       /            \
                  1 |    2 /              \ 3
                 ___v____ /                \ ________
                |        |                  |        |
                |  lwB4  |<---------------->| lwAFTR |
                |________|    Data Plane    |________|

    The numbers in each of the provisioning flows are described in more
                               detail below.

                Figure 1: Dynamic lw4o6 Provisioning Model

   The process for provisioning Lightweight 4over6 using DHCP4o6 is as

   1.  The lwB4 uses DHCPv6[RFC3315] to obtain its basic configuration.
       OPTION_DHCP4_O_DHCP6_SERVER (88) is included in the client's ORO.
       The IPv6 address of at least one DHCP4o6 server is given in the

   2.  The client sends a DHCPv4 DISCOVER message in a DHCP4o6 message
       to the DHCP4o6 server(s).  The rest of the message flow proceeds
       as per Section 5 of [I-D.fsc-softwire-dhcp4o6-saddr-opt].  The
       result is that the client is provisioned with the Ipv6 address of
       the lwAFTR, an IPv4 address and (optionally) a range of source
       ports.  The server has the /128 IPv6 address that the client will
       use its tunnel source associated with the IPv4 lease.

   3.  lwAFTR binding table maintenance is achieved by using NETCONF
       [RFC6241].  The YANG model for lw4o6 is defined in

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4.  Lightweight4over6 Dynamic Provisioning Process

   This section describes the dynamic provisioning process of
   Lightweight 4over6 in more detail.

4.1.  Client IPv6 Addressing

   Before attempting the DHCP4o6 configuration process to obtain IPv4
   configuration, the lwB4 needs to have an IPv6 address of a suitable
   scope to allow communication with the lwAFTR (e.g. a link-local
   address cannot be used).  There are no restrictions on how the
   client's IPv6 address is provisioned, (e.g.  SLAAC, DHCPv6 or some
   other mechanisms).

4.2.  DHCPv6 Configuration

   The initial configuration step is for the lwB4 to perform DHCPv6 to
   retrieve the DHCP 4o6 server's IPv6 address.  The DHCPv6 server
   provides the DHCP 4o6 server's IPv6 address by
   OPTION_DHCP4_O_DHCP6_SERVER as defined in [RFC7341].

4.3.  DHCPv4 over DHCPv6 Function

   Once the lwB4 has acquired the IPv6 address of the DHCP4o6 server,
   stateful configuration using DHCP4o6 is performed to obtain an IPv4
   address and port set.  The PSID is conveyed using DCHPv4
   OPTION_V4_PORTPARAMS (159) as decribed in [RFC7618].  The lwB4
   includes one of its active IPv6 addresses as the IPv6 tunnel source
   address in this message flow with the DHCP 4o6 server, and receives
   the lwAFTR's tunnel address through DHCP4o6, as described in section
   4 of [I-D.fsc-softwire-dhcp4o6-saddr-opt].

4.4.  lwAFTR Binding Table Maintenance

   In figure 1 above, the lwAFTR is not co-located with the DHCP 4o6
   server.  With this architecture, NETCONF [RFC6241] is used for
   syncronising client DHCP4o6 provisioning and the lwAFTR binding
   table.  A YANG model for lw4o6 is defined in [I-D.sun-softwire-yang].
   In this deployment model, the DHCP4o6 server and lwAFTR also
   implements a NETCONF server.  When an IPv4 leasing event occurs (e.g.
   DHCPACK/DHCPRELEASE messages), the DHCP4o6 server informs the
   operator's centralised configuration database of the change.

   The operator's configuration database will then use NETCONF to update
   the lwAFTR of the relevant change by adding or removing the binding
   table entry which matches the DHCP4o6 server's IPv4 address lease.

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4.4.1.  Co-located lwAFTR/DHCP4o6 Binding Table Maintenance

   In this deployment scenario, the DHCP4o6 and lwAFTR functions are
   both active on the same device.  Here, the lwAFTR maintains its
   binding table as per section 6.1 of [RFC7596] and is synchronized
   with DHCP4o6 process.  The following DHCP4o6 messages trigger binding
   table modification:

   DHCPACK:  Generated by the DHCP4o6 server, triggers lwAFTR to add a
      new entry or modify an existing entry.

   DHCPRELEASE:  Generated by lwB4, triggers lwAFTR to delete an
      existing entry.

   When the DHCP4o6 server generates a DHCPACK message, the lwAFTR looks
   up the binding table using the lwB4's IPv4 address and PSID as index.
   If there is an existing entry found, the lwAFTR updates the IPv6
   address and lifetime fields of the entry; otherwise the lwAFTR
   creates a new entry accordingly.  When the DHCP4o6 server receives a
   DHCPRELEASE message , the lwAFTR looks up the binding table using the
   lwB4's IPv6 address, IPv4 address and PSID as index.  The lwAFTR
   deletes the entry either by removing it from the binding table or by
   marking the lifetime field with an invalid value (e.g. 0).

5.  Security Considerations

   Security considerations in [RFC7596] and [RFC7341] are also relevant

   The DHCP message triggered binding table maintenance may be used by
   an attacker to send fake DHCP messages to lwAFTR.  The operator
   network should deploy [RFC2827] to prevent this kind of attack.

5.1.  Data Retention Requirements

   In some countries, regulations require a service providers to retain
   the necessary information to link IP information to a specific
   customer.  With a deterministic provisioning model, any individual
   client will always receive a pre-determined set of IPv4 provisioning
   requirements.  In this scenario, the logging requirement may be met
   by retaining information on how the DHCPv6 server has been pre-
   provisioned, with timestamp information on when changes to the pre-
   provisioning have come into effect.

   The dynamic provisioning model that is described in this document
   brings an additional logging requirement to the service provider: The
   retention logs holding allocated IPv4 address and ports, the
   associated IPv6 tunnel endpoint and timestamps marking the start and

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   end of the lease.  This is a higher logging overheard than
   deterministic provisioning, but is in line with the amount of logging
   that service providers currently have.

6.  IANA Considerations

   This document does not include an IANA request.

7.  References

7.1.  Normative References

              Farrer, I., Sun, Q., and Y. Cui, "DHCPv4 over DHCPv6
              Source Address Option", draft-fsc-softwire-dhcp4o6-saddr-
              opt-04 (work in progress), November 2015.

   [RFC2827]  Ferguson, P. and D. Senie, "Network Ingress Filtering:
              Defeating Denial of Service Attacks which employ IP Source
              Address Spoofing", BCP 38, RFC 2827, DOI 10.17487/RFC2827,
              May 2000, <http://www.rfc-editor.org/info/rfc2827>.

   [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,

   [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, <http://www.rfc-editor.org/info/rfc7596>.

   [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,

7.2.  Informative References

              Sun, Q., Wang, H., Cui, Y., Farrer, I., Boucadair, M., and
              R. Asati, "YANG Data Model for IPv4-in-IPv6 Softwire",
              draft-sun-softwire-yang-04 (work in progress), October

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   [RFC3315]  Droms, R., Ed., Bound, J., Volz, B., Lemon, T., Perkins,
              C., and M. Carney, "Dynamic Host Configuration Protocol
              for IPv6 (DHCPv6)", RFC 3315, DOI 10.17487/RFC3315, July
              2003, <http://www.rfc-editor.org/info/rfc3315>.

   [RFC6241]  Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed.,
              and A. Bierman, Ed., "Network Configuration Protocol
              (NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011,

   [RFC6887]  Wing, D., Ed., Cheshire, S., Boucadair, M., Penno, R., and
              P. Selkirk, "Port Control Protocol (PCP)", RFC 6887,
              DOI 10.17487/RFC6887, April 2013,

   [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,

Authors' Addresses

   Cong Liu
   Tsinghua University
   Department of Computer Science, Tsinghua University
   Beijing  100084

   Phone: +86-10-6278-5822
   Email: cong-liu13@mails.tsinghua.edu.cn

   Qi Sun
   Tsinghua University
   Department of Computer Science, Tsinghua University
   Beijing  100084

   Phone: +86-10-6278-5822
   Email: sunqi@csnet1.cs.tsinghua.edu.cn

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   Jianping Wu
   Tsinghua University
   Department of Computer Science, Tsinghua University
   Beijing  100084

   Phone: +86-10-6278-5983
   Email: jianping@cernet.edu.cn

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

   Email: ian.farrer@telekom.de

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