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Versions: 00 01 02

Network Working Group                                             C. Liu
Internet-Draft                                                    Q. Sun
Intended status: Informational                                     J. Wu
Expires: December 31, 2016                           Tsinghua University
                                                               I. Farrer
                                                     Deutsche Telekom AG
                                                           June 29, 2016


            Dynamic IPv4 Provisioning for Lightweight 4over6
          draft-liu-softwire-lw4over6-dynamic-provisioning-02

Abstract

   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 December 31, 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.  Dynamic Provisioning Model  . . . . . . . . . . . . . . . . .   4
     3.1.  Flow 1: lwB4's IPv6 Addressing and DHCPv6 Configuration .   4
     3.2.  Flow 2: DHCP 4o6 Function . . . . . . . . . . . . . . . .   5
     3.3.  Flow 3: lwAFTR Binding Table Maintainence . . . . . . . .   5
       3.3.1.  Flow 3a: Binding Table Maintenance for Co-located
               lwAFTR/DHCP 4o6       Functions . . . . . . . . . . .   5
       3.3.2.  Flow 3b: Binding Table Maintenance for Distributed
               lwAFTR/DHCP 4o6       Functions . . . . . . . . . . .   6
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
     4.1.  Data Retention Requirements . . . . . . . . . . . . . . .   6
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   7
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .   7
     6.2.  Informative References  . . . . . . . . . . . . . . . . .   8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   8

1.  Introduction

   Lightweight 4over6 [RFC7596] (lw4o6) provides IPv4 access over an
   IPv6 network with a 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 a core
   function of the lw4o6 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 how lw4o6 uses DHCPv4 over DHCPv6 to achieve
   dynamic IPv4 address provisioning.  The main advantages of using a
   dynamic provisioning model over a deterministic provisioning 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
      possible

   Since DHCPv4 over IPv4 cannot be used natively in a pure IPv6
   network, DHCPv4 over DHCPv6 (DHCP 4o6) [RFC7341] allows DHCPv4
   messages to be trasported over a pure IPv6 network by encapsulating
   DHCPv4 messages into specific DHCPv6 options and messages.

   Note that the dynamic provisioning decouples the IPv6 and IPv4
   addresses, the binding info required by lwAFTR turns to be an
   ayschronous combiantion of (restricted) IPv4 address and IPv6
   address.  [I-D.fsc-softwire-dhcp4o6-saddr-opt] defines a DHCP 4o6
   based mechanism for the lwB4 to inform the server of its binding
   between dynamically allocated IPv4 address and Port Set ID and the
   IPv6 address that it will use for accessing IPv4-over-IPv6 services

   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 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.




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   Determinstic provisioning: Lightweight B4 provisioning with DHCPv6 as
   described in section 5.1 of [RFC7596].  The IPv4 address, restricted
   port set and the address of lwAFTR are carried in DHCPv6 options
   defined in [RFC7598].

   Dynamic provisioning: Lightweight B4 provisioning with DHCPv4 over
   DHCPv6 as described in this document.  The IPv4 address and
   rescricted port set are allocated through DHCP 4o6 transport as
   defined in [RFC7341].  The allocation of lwAFTR's IPv6 address is
   descirbed in [I-D.fsc-softwire-dhcp4o6-saddr-opt].

3.  Dynamic Provisioning Model

   As shown in Figure 1, the dynamic provisioning model consists of four
   functional elements: lwB4, lwAFTR, DHCPv6 Server and DHCP 4o6 Server.
   Note that these elements are not necessarily separate devices, one or
   more functional elements could be located on a single device.  One
   existing example of this is the co-location of the DHCP 4o6 Server
   and lwAFTR as a single gateway device.  The differences in the
   message flow from this co-location are also described below.

                 ________     __________
                |        |   |          |
                | DHCPv6 |   | DHCP 4o6 |
                | Server |   |  Server  |
                |________|   |__________|
                    ^       /            \
                  1 |    2 /              \ 3a/b
                 ___v____ /                \ ________
                |        |                  |        |
                |  lwB4  |<---------------->| lwAFTR |
                |________|    Data Plane    |________|

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

                Figure 1: Dynamic lw4o6 Provisioning Model

3.1.  Flow 1: lwB4's IPv6 Addressing and DHCPv6 Configuration

   Before attempting the DHCP 4o6 configuration process to obtain IPv4
   configuration, the lwB4 requires an IPv6 address of a suitable scope
   to allow communication with the lwAFTR (e.g. a link-local address
   cannot be used).  This IPv6 address can be configured using any
   applicable method (e.g.  SLAAC, DHCPv6, etc.).

   To enable DHCPv4 over DHCPv6 transport, the lwB4 needs to perform
   DHCPv6 to retrieve the DHCP 4o6 server's IPv6 address.  The option



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   code OPTION_DHCP4_O_DHCP6_SERVER (88) is included in the client's
   ORO.  The DHCPv6 server responds the DHCP 4o6 server's IPv6 address
   by carrying the addresses in DHCP 4o6 Server Address option as
   defined in [RFC7341].

3.2.  Flow 2: DHCP 4o6 Function

   Once the lwB4 has acquired the IPv6 address of the DHCP 4o6 server,
   stateful configuration using DHCP 4o6 is performed to obtain an IPv4
   address and (optionally) a port set.  The lwB4 sends a DHCPv4
   DISCOVER message in a DHCPv4-query Message to the DHCP 4o6 server(s)
   to activate the DHCP 4o6 transport.  To obtain a shared IPv4 address,
   the lwB4 also has to include Parameter Request List option with the
   option code OPTION_V4_PORTPARAMS (159) as described in [RFC7618].

   To obtain the IPv6 address of lwAFTR and inform the DHCP4o6 server of
   the lwB4's IPv6 tunnle source address, the message flow described in
   section 5 of [I-D.fsc-softwire-dhcp4o6-saddr-opt] is followed by the
   lwB4.

   Once successfully completed, the client has been 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.

3.3.  Flow 3: lwAFTR Binding Table Maintainence

   As stated in [RFC7596], the lwAFTR MUST synchronize the binding
   information with the port-restricted address provisioning process.
   In the dynamic provisioning model described in this document, once
   the lwB4's provisioning process is completed and the DHCP 4o6 server
   holds the client's /128 IPv6 tunnel endpoint address, this binding
   information can be syncronized with the lwAFTR.  The method for this
   synchronization is dependent on whether the DHCP 4o6 and lwAFTR
   functions are co-located on the same physical host.

3.3.1.  Flow 3a: Binding Table Maintenance for Co-located lwAFTR/DHCP
        4o6 Functions

   Here, the lwAFTR maintains its binding table as per section 6.1 of
   [RFC7596] and is synchronized with DHCP 4o6 process.  The following
   DHCP 4o6 messages trigger binding table modification:

   DHCPACK:  Generated by the DHCP 4o6 server, triggers lwAFTR to add a
      new entry or modify an existing entry.

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



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   When the DHCP 4o6 server generates a DHCPACK message, information
   about the new lease including the client's IPv6 tunnel endpoint
   address and IPv4 address/PSID tuple is sent to the lwAFTR process.
   The lwAFTR performs a check that this new binding does not match an
   existing binding (both the v6 and v4 information must be checked
   independently to ensure no conflicts).  If no conflicts are found the
   lwAFTR creates a new binding table entry for the client.

   If there an existing entry is found, the lwAFTR updates the IPv6
   address and lifetime fields of the entry.

   When the DHCP 4o6 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).

3.3.2.  Flow 3b: Binding Table Maintenance for Distributed lwAFTR/DHCP
        4o6 Functions

   With this architecture, NETCONF [RFC6241] is used for syncronising
   client DHCP 4o6 provisioning and the lwAFTR binding table.  A YANG
   model for lw4o6 is defined in [I-D.sun-softwire-yang].  In this
   deployment model, the DHCP 4o6 server and lwAFTR also implements a
   NETCONF server.  When an IPv4 leasing event occurs (DHCPACK/
   DHCPRELEASE messages, or an active lease expiring), the DHCP 4o6
   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 he DHCP 4o6 server's IPv4 address lease.

4.  Security Considerations

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

   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.

4.1.  Data Retention Requirements

   In some countries, regulations require a service providers to retain
   the necessary information to link IP allocatoin information to a
   specific customer at a specific point in time.




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   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
   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.

5.  IANA Considerations

   This document does not include an IANA request.

6.  References

6.1.  Normative References

   [I-D.fsc-softwire-dhcp4o6-saddr-opt]
              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,
              <http://www.rfc-editor.org/info/rfc7341>.

   [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,
              <http://www.rfc-editor.org/info/rfc7618>.




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6.2.  Informative References

   [I-D.sun-softwire-yang]
              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
              2015.

   [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,
              <http://www.rfc-editor.org/info/rfc6241>.

   [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,
              <http://www.rfc-editor.org/info/rfc6887>.

   [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,
              <http://www.rfc-editor.org/info/rfc7598>.

Authors' Addresses

   Cong Liu
   Tsinghua University
   Department of Computer Science, Tsinghua University
   Beijing  100084
   P.R.China

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












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   Qi Sun
   Tsinghua University
   Department of Computer Science, Tsinghua University
   Beijing  100084
   P.R.China

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


   Jianping Wu
   Tsinghua University
   Department of Computer Science, Tsinghua University
   Beijing  100084
   P.R.China

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


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

   Email: ian.farrer@telekom.de
























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