Gateway-Initiated 4over6 Deployment
draft-chen-softwire-gw-init-4over6-01

Network Working Group                                            Y. Chen
Internet-Draft                                                     J. Wu
Intended status: Informational                       Tsinghua University
Expires: August 28, 2013                                         X. Tang
                                         China Unicom Research Institute
                                                       February 24, 2013

                  Gateway-Initiated 4over6 Deployment
                 draft-chen-softwire-gw-init-4over6-01

Abstract

   Gateway-Initiated 4over6 (GI-4over6) is a variant of 4over6
   mechanisms which include Public 4over6
   ([I-D.ietf-softwire-public-4over6]) and Lightweight 4over6
   ([I-D.cui-softwire-b4-translated-ds-lite]), and it's designed to
   satisfy the certain tunnel-based access scenario.  The GI-4over6
   extends the On-Link Client Relay Agent (LCRA) that is defined in
   [I-D.ietf-dhc-dhcpv4-over-ipv6] and thus makes it enabled to help
   gateway device perform 4over6 CE function described in
   [I-D.ietf-softwire-public-4over6], and lwB4 function described in
   [I-D.cui-softwire-b4-translated-ds-lite], while the public IPv4
   addresses (and available ports) are assigned to the end hosts that
   behind the gateway device.

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   This Internet-Draft will expire on August 28, 2013.

Copyright Notice

   Copyright (c) 2013 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   This document is subject to BCP 78 and the IETF Trust's Legal
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Table of Contents

   1.  Overview . . . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Requirements Language  . . . . . . . . . . . . . . . . . . . .  4
   3.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  5
   4.  GI-4over6 Architecture . . . . . . . . . . . . . . . . . . . .  6
   5.  4over6 Gateway Behaviors . . . . . . . . . . . . . . . . . . .  7
     5.1.  Public 4over6 Mode . . . . . . . . . . . . . . . . . . . .  7
     5.2.  Lightweight 4over6 Mode  . . . . . . . . . . . . . . . . .  7
   6.  Relative Considerations  . . . . . . . . . . . . . . . . . . .  9
     6.1.  Consideration for IPv4 Gateway of Customer End Hosts . . .  9
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 10
   8.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 11
     8.1.  Normative References . . . . . . . . . . . . . . . . . . . 11
     8.2.  Informative References . . . . . . . . . . . . . . . . . . 11
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12

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1.  Overview

   Gateway-Initiated 4over6 (GI-4over6) is a variant of 4over6
   mechanisms which include Public 4over6
   ([I-D.ietf-softwire-public-4over6]) and Lightweight 4over6
   ([I-D.cui-softwire-b4-translated-ds-lite]), and it's designed to
   satisfy the certain tunnel-based access scenario.

   [I-D.ietf-dhc-dhcpv4-over-ipv6] describes a way for communication
   between traditional DHCPv4 clients with DHCPv4 servers over IPv6-only
   transport.  The On-Link Client Relay Agent (LCRA) defined in the
   draft can serve any DHCPv4 client on the same link.

   If the 4over6 tunnel initiator is the gateway device, and if the DHCP
   client on the end host behind the gateway device wants to communicate
   with the remote DHCP server on the tunnel concentrator, and get IPv4
   provision from the tunnel concentrator directly, the gateway device
   must perform the LCRA function to relay the DHCP messages between the
   end hosts and the remote DHCP server.  When it comes to the
   lightweight 4over6 scenario, if the end host cannot perform as a
   lwB4, but still wants to get an public IPv4 address, then the data
   plane function of lwB4 must be performed by the gateway device, and
   the LCRA on the gateway must extract the port-set information (i.e.
   the DHCP Port-Set Option defined in [I-D.sun-dhc-port-set-option])
   from the DHCP response from the DHCP server, and help the gateway
   device maintains the state of binding between the identifier of the
   end host and the port-set.

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2.  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 [RFC2119].

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3.  Terminology

   This document uses the terms defined in
   [I-D.ietf-dhc-dhcpv4-over-ipv6], [I-D.ietf-softwire-public-4over6],
   [I-D.cui-softwire-b4-translated-ds-lite] and
   [I-D.sun-dhc-port-set-option].

   The other terms used are described as follows:

   Customer End Host: The end host in the customer IPv4 network behinds
   the 4over6 Gateway.  It should perform as a DHCP client and
   communicate with DHCP server on the tunnel concentrator through
   DHCPv4 over IPv6 mechanism.

   4over6 Gateway: The gateway device located at the border of the
   customer IPv4 network and the IPv6 ISP network.  In the Public 4over6
   scenario, the 4over6 Gateway should perform the 4over6 CE function.
   And in the Lightweight 4over6 scenario, the 4over6 Gateway should act
   as the LwB4.

   4over6 Tunnel Concentrator: The border router located between the
   IPv6 ISP network and the Internet.  In the Public 4over6 scenario,
   the 4over6 Tunnel Concentrator refers to 4over6 CE.  And in the
   Lightweight 4over6 scenario, the 4over6 Tunnel Concentrator refers to
   LwAFTR.

   EX-LCRA: The LCRA with the extended function described in the
   document.  It is assumed to be co-located with the 4over6 Gateway.
   It could be deployed in ohter ways depending on the actual deployment
   requirements, and they are out of the scope of this document.

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4.  GI-4over6 Architecture

   The general architecture of GI-4over6 is illustrated as Figure 1.
   The Customer End Host in the Customer IPv4 Network could be an IPv4
   or dual-stack host.  The 4over6 Gateway is a dual-stack gateway
   device provided by the ISP, and has been already enabled to support
   EX-LCRA.

  +------------------+           +-------------------------+
  | +----------+     |           |                         |
  | | Customer |   +-+-----------+-+                     +-+-------------+   +----------+
  | | End Host +---+ 4over6        | IPv4-in-IPv6 tunnel | 4over6 Tunnel |   |          |
  | +----------+   | Gateway       |=====================| Concentrator  +---+ Internet |
  | +----------+   | (with EX-LCRA)|                     | (with TSV)    |   |          |
  | | Customer +---+               |  IPv6 ISP Network   +-+-------------+   +----------+
  | | End Host |   +-+-----------+-+                       |
  | +----------+     |           |                         |
  | Customer IPv4    |           +-------------------------+
  | Network          |
  +------------------+

   Figure 1 GI-4over6 Architecture

   There are two major scenarios: Public 4over6 Scenario and Lightweight
   4over6 Scenario.  We assume that in both of the scenario the Customer
   End Host needs to get public IPv4 access, and the DHCP client on the
   Customer End Host has to stay traditional (i.e. without any extension
   to support DHCPv4 over IPv6 transport or Port-Set Option).  Hence the
   actual 4over6 tunnel initiator should be the 4over6 Gateway.  And in
   both scenarios, we assume that there is a 4over6 tunnel that has been
   established already between the 4over6 Gateway and the 4over6 Tunnel
   Concentrator.

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5.  4over6 Gateway Behaviors

   The 4over6 Gateway should act differently in the two major scenarios,
   which means that the 4over6 Gateway has 2 modes of behaviors.  We
   name them with Public 4over6 Mode and Lightweight 4over6 Mode.  The
   EX-LCRA MUST function in either of the two modes at the same time,
   depending on the actual scenario it is in.

5.1.  Public 4over6 Mode

   In the Public 4over6 Scenario, the 4over6 Gateway must perform the
   4over6 CE function on the data plane.  The Customer End Hosts should
   get the full public IPv4 addresses directly from the TSV, not any
   other DHCP server.  Therefore, the EX-LCRA must perform the LCRA
   function described in the Section 6 of
   [I-D.ietf-dhc-dhcpv4-over-ipv6].

   Note that if there is a Port-Set Option in any of the DHCP message
   going through, the EX-LCRA MUST discard the message.

5.2.  Lightweight 4over6 Mode

   In the Lightweight 4over6 Scenario, the 4over6 Gateway must perform
   the LwB4 function on the data plane.  The Customer End Hosts should
   get the public IPv4 addresses and available ports from the TSV, not
   any other DHCP server.  In this case, the EX-LCRA must perform the
   LCRA function described in the Seciton 6 of
   [I-D.ietf-dhc-dhcpv4-over-ipv6], and the EX-LCRA MUST also handle the
   Port-Set Option of the DHCP messages.

   For the DHCPDISCOVER message sent by Customer End Host, the EX-LCRA
   MUST add the Option Code of the Port-Set Option into the DHCP
   Parameter Request List Option (Option Code 55) of the message.

   For the DHCPOFFER message sent by TSV, the EX-LCRA MUST extract the
   Port-Set Option from the message, and store the match of Client
   Identifier and the values of Port Set Index and Port Set Mask of the
   Port-Set Option in a binding table.  The EX-LCRA MAY erase the Port-
   Set Option from the DHCPOFFER message then.  Note that if the
   received DHCPOFFER message doesn't include the Port-Set Option, the
   EX-LCRA MUST discard the message.

   For the DHCPREQUEST message sent by Customer End Host, the EX-LCRA
   should look into the binding table and search for the Client
   Identifier carried by the message.  If there is an entry that
   matches, the EX-LCRA should get the values of the Port Set Index and
   Port Set Mask from the entry, and add the Port-Set Option with theses
   values into the DHCPREQUEST message.

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   For the DHCPACK message sent by TSV, the EX-LCRA MUST extract the
   Port-Set Option from the message, and look into the binding table and
   search for the Client Identifier carried by the message.  If there is
   an entry that matches, the EX-LCRA should update the values of the
   Port Set Index and Port Set Mask of the entry with the values of the
   corresponding field of the Port-Set Option in the DHCPACK message,
   and enable the binding on the data plane of the 4over6 Gateway.

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6.  Relative Considerations

6.1.  Consideration for IPv4 Gateway of Customer End Hosts

   As the TSV is co-located with the 4over6 Tunnel Concentrator and is
   not in the local IPv4 network, it may not include the correct IPv4
   address of the 4over6 Gateway in the DHCP Router Option (Option Code
   3), which is the actual gateway and access entrance for the Customer
   End Hosts.  Thus the outbound IPv4 sessions on the Customer End Host
   may fail because of the lack of default gateway information.  In
   order to get rid of this issue, the EX-LCRA may modify the value of
   the DHCP Router Option of the DHCP response messages from the remote
   DHCP server, and input the IPv4 address of the 4over6 Gateway on the
   LAN side as the value of the DHCP Router Option, when the messages
   are going to pass through.

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7.  Security Considerations

   The security considerations of the document is well described in all
   the references, and the document raises barely new security issues.

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8.  References

8.1.  Normative References

   [I-D.cui-softwire-b4-translated-ds-lite]
              Cui, Y., Sun, Q., Boucadair, M., Tsou, T., Lee, Y., and I.
              Farrer, "Lightweight 4over6: An Extension to the DS-Lite
              Architecture", draft-cui-softwire-b4-translated-ds-lite-10
              (work in progress), February 2013.

   [I-D.ietf-dhc-dhcpv4-over-ipv6]
              Cui, Y., Wu, P., Wu, J., and T. Lemon, "DHCPv4 over IPv6
              Transport", draft-ietf-dhc-dhcpv4-over-ipv6-05 (work in
              progress), September 2012.

   [I-D.ietf-softwire-public-4over6]
              Cui, Y., Wu, J., Wu, P., Vautrin, O., and Y. Lee, "Public
              IPv4 over IPv6 Access Network",
              draft-ietf-softwire-public-4over6-04 (work in progress),
              October 2012.

   [I-D.sun-dhc-port-set-option]
              Sun, Q., Lee, Y., Sun, Q., Bajko, G., and M. Boucadair,
              "Dynamic Host Configuration Protocol (DHCP) Option for
              Port Set Assignment", draft-sun-dhc-port-set-option-00
              (work in progress), October 2012.

8.2.  Informative References

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

   [RFC4925]  Li, X., Dawkins, S., Ward, D., and A. Durand, "Softwire
              Problem Statement", RFC 4925, July 2007.

   [RFC6674]  Brockners, F., Gundavelli, S., Speicher, S., and D. Ward,
              "Gateway-Initiated Dual-Stack Lite Deployment", RFC 6674,
              July 2012.

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Authors' Addresses

   Yuchi Chen
   Tsinghua University
   Department of Computer Science, Tsinghua University
   Beijing,   100084
   P.R.China

   Phone: +86 10 6278 5822
   Email: chenycmx@gmail.com

   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

   Xiongyan Tang
   China Unicom Research Institute
   33 Erlong Road, Xicheng District
   Beijing,   100032
   P.R.China

   Phone: +86 10 6652 2558
   Email: tangxy@chinaunicom.cn

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