Network Working Group                                             Q. Sun
Internet-Draft                                                    C. Xie
Intended status: Informational                             China Telecom
Expires: January 4, 2018                                          Y. Lee
                                                                 M. Chen
                                                                   T. Li
                                                     Tsinghua University
                                                               I. Farrer
                                                     Deutsche Telekom AG
                                                            July 3, 2017

            Deployment Considerations for Lightweight 4over6


   Lightweight 4over6 is a mechanism for providing IPv4 services to
   clients connected to a single-stack IPv6 network.  The architecture
   is similar to DS-Lite, but the network address translation function
   is relocated from the tunnel concentrator to the tunnel client, hence
   reducing the amount of state which must be maintained in the
   concentrator to a per-customer level.  This document discusses the
   applicability, describes various deployment models and provides
   deployment considerations for Lightweight 4over6.

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
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   Internet-Drafts are draft documents valid for a maximum of six months
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   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on January 4, 2018.

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Copyright Notice

   Copyright (c) 2017 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
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   ( in effect on the date of
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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Deployment Models . . . . . . . . . . . . . . . . . . . . . .   4
     2.1.  Top-Down Deployment Model . . . . . . . . . . . . . . . .   4
     2.2.  Bottom-Up Deployment Model  . . . . . . . . . . . . . . .   5
     2.3.  Campus Deployment . . . . . . . . . . . . . . . . . . . .   5
   3.  Overall Deployment Considerations . . . . . . . . . . . . . .   5
     3.1.  IP Addressing and Routing . . . . . . . . . . . . . . . .   5
       3.1.1.  IPv4 Routing  . . . . . . . . . . . . . . . . . . . .   5
       3.1.2.  IPv6 Routing  . . . . . . . . . . . . . . . . . . . .   6
     3.2.  lwB4 Configuration  . . . . . . . . . . . . . . . . . . .   6
       3.2.1.  DHCPv6 Based Provisioning . . . . . . . . . . . . . .   6
       3.2.2.  DHCPv4 over DHCPv6 Based Provisioning . . . . . . . .   7
       3.2.3.  PCP Based Provisioning  . . . . . . . . . . . . . . .   7
       3.2.4.  NETCONF/YANG Based Provisioning . . . . . . . . . . .   7
       3.2.5.  Other lwB4 Configuation Considerations  . . . . . . .   7
     3.3.  lwAFTR Discovery  . . . . . . . . . . . . . . . . . . . .   8
     3.4.  Impacts on Accouting  . . . . . . . . . . . . . . . . . .   8
   4.  lwAFTR Deployment Considerations  . . . . . . . . . . . . . .   8
     4.1.  Logging at the lwAFTR . . . . . . . . . . . . . . . . . .   9
     4.2.  MTU and Fragmentation Considerations  . . . . . . . . . .   9
     4.3.  Reliability Considerations of lwAFTR  . . . . . . . . . .   9
     4.4.  Location of lwAFTRs in the Network  . . . . . . . . . . .  10
     4.5.  Path Consistency Consideration  . . . . . . . . . . . . .  10
   5.  lwB4 Deployment Considerations  . . . . . . . . . . . . . . .  11
     5.1.  NAT Traversal Issues  . . . . . . . . . . . . . . . . . .  11
     5.2.  Static Port Forwarding Configuration  . . . . . . . . . .  11
   6.  DS-Lite Compatibility Consideration . . . . . . . . . . . . .  12
     6.1.  Case 1: Integrated Network Element with Lightweight
           4over6      and DS-Lite AFTR Scenario . . . . . . . . . .  12
     6.2.  Case 2: DS-Lite Coexistent scenario with Separated AFTR .  13
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  14

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   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  14
   Appendix A.  China Telecom Experimental Results . . . . . . . . .  17
     A.1.  Experimental Environment  . . . . . . . . . . . . . . . .  18
     A.2.  Experimental Results  . . . . . . . . . . . . . . . . . .  19
     A.3.  Conclusions . . . . . . . . . . . . . . . . . . . . . . .  20
   Appendix B.  Tsinghua University Experimental Result  . . . . . .  20
     B.1.  Experimental Environment  . . . . . . . . . . . . . . . .  20
     B.2.  Experimental Results  . . . . . . . . . . . . . . . . . .  21
     B.3.  Conclusion  . . . . . . . . . . . . . . . . . . . . . . .  22
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  22

1.  Introduction

   Lightweight 4over6 [RFC7596] (lw4o6) is an extension to DS-Lite
   [RFC6333] which simplifies the AFTR module by relocating the NAPT
   function among B4 elements located at the subscriber's premises.  In
   the lw4o6 architecture, the functional elements are referred to as
   the lwB4 and lwAFTR.

   The lwB4 is provisioned with an IPv6 address, a public IPv4 address
   and a port-set.  It performs port-restricted NAPT on subscriber's
   packets using the provisioned public IPv4 address and port-set.  IPv4
   packets are routed between the lwB4 and the lwAFTR encapsulated in an
   IPv4 in IPv6 Softwire.  The lwAFTR maintains one binding entry per-
   subscriber, consisting of the lwB4's IPv6 tunnel endpoint, IPv4
   address and port-set.  Section 4.4 of [RFC6346] provides more detail
   of this mechanism.

   This can bring a number of advantages when compared to DS-Lite:

   o  Per-subscriber configuration allows for the operator to provision
      each subscriber according to their specific service requirements.

   o  The logging requirements to meet regulatory requirements may be
      reduced as it is only necessary to log when a subscriber is
      provisioned or de-provisioned in the lwAFTR.  This relaxes the
      need for logging on a per-session, or per port block allocation.

   o  In some lw4o6 deployment topologies, the removal of per-session
      state means that it is possible to have very large parallelisation
      of lwAFTR elements.  This offers excellent scaling and resilience.

   o  This mechanism preserves the dynamic feature of IPv4/IPv6 address
      binding as in DS-Lite, so it has no coupling between IPv6 address
      and IPv4 address/port-set as any full stateless solution
      ([RFC6052] or [RFC7597]) requires.

   The terminology used in this document follows the definitions and

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   abbreviations from [RFC6333] and [RFC7596].

2.  Deployment Models

   Lightweight 4over6 is suitable for operators who would like to free
   any correlation of the IPv6 address with IPv4 address and port-set,
   as the IPv4 addressing is an overlay to the IPv6 addressing
   architecture.  Thus, IPv6 addressing is completely flexible to fit
   other deployment requirements, e.g., auto-configuration, service
   classification, user management, QoS support, etc.

   Lightweight 4over6 can be deployed in a residential ISP network
   (depicted in Figure 1).  In this scenario, a lwB4 acquires an IPv4
   address and a port-set alongside IPv6 provisioning, including an
   address for the lwAFTR.  It then establishes an IPv4-in-IPv6 softwire
   to the lwAFTR.  The lwB4 function may be implemented in a CPE
   providing IPv4 services for a home network, or directly in a host.

   The lwAFTR holds a table with the bindings between the lwB4's IPv6
   addresses and their allocated IPv4 addresses + port sets.  The
   supporting system is used to syncronise the lwB4 and lwAFTR binding
   information.  It may also be used for logging and user management.

                            |   Supporting  |
                            |     System    |
                    |                             |
+---------+  +------+---+                         |
|  Host   |  |   lwB4   |        _  _             |
|         |--|          |=======( `  )=======+----+----+   +-----------+
+---------+  +----------+     (        ) _   |         |   |   IPv4    |
                             (   IPv6   ) )  | lwAFTR  |---| Internet  |
+---------+  +------+---+     ( Network  )   |         |   |           |
|  Host   |--|   lwB4   |====( (       ) ====+---------+   +-----------+
|         |  |          |      `(_, __)
+---------+  +----------+

                      Figure 1 Architectural Overview

2.1.  Top-Down Deployment Model

   In the top-down deployment model, the supporting system holds the
   overall binding table for the network.  It uses this to pre-provision
   the local binding table entries for the lwAFTR and also provision
   lwB4s with the correct configuration (e.g. using DHCPv6 or PCP).

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   With this method, one binding table entry can be present on lwAFTRs
   and stateless failover can be achieved.

2.2.  Bottom-Up Deployment Model

   In the bottom-up model, the client is first provisioned with the
   relevant paramters necessary for building the softwire.  It then
   attempts to send traffic to the lwAFTR.

   On receipt of lwB4 traffic which does not have an existing binding-
   table entry, one is dynamically created.  The lwAFTR reports the new
   binding entry to the supporting system.
   [I-D.ietf-behave-syslog-nat-logging] or
   [I-D.ietf-behave-ipfix-nat-logging] may be used for this purpose.  In
   this way, the lwAFTR can determine the binding by its own and there
   is little impact on existing network architecture.

2.3.  Campus Deployment

   Lightweight 4over6 can also be deployed in a campus or enterprise
   network, (depicted in Figure 2).  In this scenario, a lwB4 acts as a
   gateway router for a number of hosts.  The lwB4 is first provisioned
   with an IPv4 address and port-set.  It then establishes an IPv4-in-
   IPv6 softwire using the IPv6 address to deliver IPv4 services to its
   connected host via the lwAFTR in the network.  A network management
   system could be used to receive statistic information of the network
   equipments, such as the binding table, network load, and connected
   device.  NETCONF [RFC6241] could be used for syncronising lwB4's IPv6
   address and its allocated IPv4 address + port set with the lwAFTR.
   The network management system may keep the binding information as
   well for logging and user management.

3.  Overall Deployment Considerations

3.1.  IP Addressing and Routing

   In Lightweight 4over6, there is no inter-dependency between the IPv4
   and IPv6 addressing schemes.  This allows for complete flexibilty in
   addressing architecture.

3.1.1.  IPv4 Routing

   The IPv4 addresses/prefixes that are allocated to customer's lwB4s
   are advertised to the IPv4 Internet as being reachable via the
   lwAFTR(s).  If multiple lwAFTRs are all serving the same set of
   lwB4s, all will advertise the same IPv4 reachable routes.

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3.1.2.  IPv6 Routing

   The lwAFTR provides a /128 IPv6 tunnel endpoint address which is
   advertsed to the lwB4s.  If multiple lwAFTRs are all serving the same
   set of lwB4s, all will advertise the same IPv6 tunnel endpoing

   The lwB4's IPv6 addressing and routing, there are no specific
   topological limitations.  An existing IPv6 address and routing
   architecture should not be affected.  For example, in PPPoE scenario,
   a CPE could obtain a prefix via DHCPv6 prefix delegation, and the
   hosts behind CPE would get its own IPv6 addresses within the prefix
   through SLAAC or DHCPv6 statefully.  This IPv6 address assignment
   procedure has nothing to do with restricted IPv4 address allocation.

   It is worth noting that if the Top-Down provisioning model is chosen,
   then there must be determinism in the local address that the lwB4
   uses for building its tunnel.  This is so that the binding entry for
   the lwB4 can be pre-provisioned in the lwAFTR.  [RFC7598] offers a
   solution for this using the 'bind-ipv6-prefix' field is used to
   inform the lwB4 which configured prefix to use.  The suffix is then
   created according to Section 6 of [RFC7597].

3.2.  lwB4 Configuration

   In lw4o6, each lwB4 will get its restricted IPv4 address and a port-
   set after successful user authentication process and IPv6
   provisioning process.  This assignment can been achieved using a
   number of methods:

   o  DHCPv6 Softwire S46 Option [RFC7598]

   o  DHCPv4 over DHCPv6 [RFC7341], [RFC7618] and

   o  PCP [RFC7753]

   o  NETCONF/YANG [I-D.ietf-softwire-yang]

3.2.1.  DHCPv6 Based Provisioning

   [RFC7598] describes a set of DHCPv6 options used for provisioning
   lw4o6 clients.  OPTION_S46_CONT_LW (96) is a DHCPv6 contatiner
   option, which can hold the IPv6 of the lwAFTR (OPTION_S46_BR (90)),
   the lwB4's IPv4 address and IPv6 prefix hint (OPTION_S46_V4V6BIND
   (92)), and port set information (OPTION_S46_PORTPARAMS (93)).

   In this model, the DHCPv6 server needs to be pre-provisioned with the

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   client configuration.  Therefore, this approach is better suited to
   client configurations that will be long-lived.

   DHCPv6 based provisioning can also be used in conjunction with a AAA
   server.  [I-D.ietf-softwire-map-radius] decribes this function.

3.2.2.  DHCPv4 over DHCPv6 Based Provisioning

   An operator may use DHCPv4 to provision IPv4 address to the lwB4.  In
   a typical deployment, the DHCP server is a centralized DHCP server
   and lwAFTR is the DHCP relay agent to relay the dhcp messages to the
   server over unicast.  Rarely DHCP server will collocate with the
   lwAFTR to provision IPv4 resources to the lwB4.

3.2.3.  PCP Based Provisioning

   Operator may also use PCP Port-set Option to provision IPv4 address
   and port-set to the lwB4.  In a typical deployment, PCP server will
   collocate with lwAFTR, and the subscriber's binding can be determined
   by lwAFTR.  The PCP request should be sent to the lwAFTR's tunnel
   end-point address.  It is not common that PCP server will be
   centralized deployed in which the lwAFTR is the PCP proxy to relay
   PCP requests.

3.2.4.  NETCONF/YANG Based Provisioning

   Operators using NETCONF to manage customer devices can provision
   lw4o6 using [I-D.ietf-softwire-yang].

3.2.5.  Other lwB4 Configuation Considerations

   Some operators may offer different service level agreements (SLA) to
   users that some users may require more ports then others.  In this
   deployment scenario, the operator can implement differentiated
   policies in provisioning system specified to a user's lwB4 or a group
   of lwB4s to allocate a certain range of port-set.  The lwAFTR may
   also run multiple instances with different port-set sizes to build
   the mapping table.

   It is also worth noting the compatibility between lw4o6 and Public
   IPv4 over IPv6 [RFC7040].  When a lw4o6 client is provisioned with a
   'full' IPv4 address (i.e. with no port-set or a port-set that allows
   the use of all of the L4 ports), then the A+P routing model is no
   longer used by the lwAFTR as traffic is routed on the IPv4 address
   only.  This function can be useful when a subscriber usses protocols
   which do not have L4 ports.

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3.3.  lwAFTR Discovery

   The lwB4 needs to discover the lwAFTR's IPv6 address before it is
   able to set up the softwire tunnel and provide any IPv4 services.
   This address can be learned through an out-of-band channel, static
   configuration, or dynamic configuration.  In practice, Lightweight
   4over6 lwB4 can use the same DHCPv6 option [RFC6334] to discover the
   FQDN of the lwAFTR.

   When Lightweight 4over6 is deployed in the same place with DS-Lite,
   either different FQDNs can be configured for Lightweight 4over6 and
   DS-Lite separately or different DHCPv6 options can be used for
   Lightweight 4over6 [RFC7598] and DS-Lite.  More detailed
   considerations on DS-Lite compatibility will be discussed in
   Section 6.

   The lw4o6 DHCPv6 option (OPTION_S46_LW_CONT (96)) can contain
   OPTION_S46_BR (90) which holds the v6 address of the lwAFTR.

3.4.  Impacts on Accouting

   In lw4o6, the accounting impact due to the tunneling protocol is the
   same with DS-Lite (see section 6.2 of [RFC6908]).  However, since in
   lw4o6, the IPv4 service is only available after port-set allocation,
   if operators regard IPv4 service as a on-demand value-added service,
   e.g.  IPv6 connectivity is offered by default, while IPv4
   connectivity will be offered untill a subscriber requires, etc., IPv4
   service accounting should start after port-set allocation has

   It should be noted that in common with all A+P mechanisms, lw4o6 can
   not performing per-session logging in the way that CGN based
   solutions do.

4.  lwAFTR Deployment Considerations

   As Lightweight 4over6 is an extension to DS-Lite, both technologies
   share similar deployment considerations.  For example: the interface
   considerations, lawful intercept considerations, blacklisting a
   shared IPv4 Address, AFTR policies, and impacts on accounting
   processes described in [RFC6908] are also applicable here.  This
   document only discusses addtional considerations specific to
   Lightweight 4over6.

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4.1.  Logging at the lwAFTR

   In lw4o6, operators only log one entry per subscriber.  Each log
   needs to include subscriber's IPv6 address used for the softwire, the
   public IPv4 address and the allocated port-set, and the start and end
   times that the binding entry was valid for.

   To ensure consistency of the logged information, the port set
   algorithm implemented in lw4o6 lwAFTR needs to be synchronized with
   the one implemented in the logging system.  For example, if
   contiguous port-set algorithm is adopted in the lwAFTR, the same
   algorithm needs to be applied for the logging system.

   Since the binding in lwAFTR does not log sessions as they are set up,
   operators should be aware that lw4o6 does not provided a mechanism
   for destination-specific logging.

4.2.  MTU and Fragmentation Considerations

   As Lightweight 4over6 uses a tunneling protocol, the same
   considerations regarding fragmentation and reassembly as for DS-Lite
   [RFC6908] are applicable.  In order to avoid the problems that are
   associated with fragmentation, it is advisable to ensure that the MTU
   across the IPv6 domain between the lwB4 and lwAFTR is large enough to
   allow for the transportation of IPv4 packets plus the 40-byte
   overhead for IPv6 encapsulation.

4.3.  Reliability Considerations of lwAFTR

   Operators may deploy multiple lwAFTRs for robustness, reliability,
   and load balancing.  In lw4o6, subscriber to IPv4 and port-set
   mapping needs to be pre-provisioned in the lwAFTR before an IPv4
   service can be provided.

   For redundancy, one or more backup lwAFTR can have the subscriber
   bindings already provisioned, e.g. as part of the top-down
   provisioning process described above.  In this case, the provisioning
   system is responsible for ensuring that the binding tables of the
   lwAFTRS are consistent.  In this case, as customer traffic arriving
   or returning through either of the lwAFTRs will be processed in the
   same way, an active/active redundancy model is possbile.

   A second option, which could be more suitable for bottom-up
   provisioning, is for the bindings to be replicated between the
   primary lwAFTR and the backup lwAFTR.  When the primary lwAFTR fails,
   the backup lwAFTR has the necessary binding table entries to
   correctly forward subscriber traffic.  In this mode, the internal
   hosts are not required to re-initiate the bindings with the external

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   hosts.  In lw4o6, as the number of binding states have been greatly
   reduced compared to DS-Lite, it is reasonable to adopt Hot Standby
   mode when there are only two lwAFTRs (a primary and a backup lwAFTR).
   However, if the number of lwAFTRs is larger than two, it is not
   scalable to deploy using hot standby mode since each two of the
   lwAFTRs should to syncronize the binding states.

4.4.  Location of lwAFTRs in the Network

   lwAFTR(s) can be deployed in a centralized or a distributed manner.

   For a centralized deployment, the lwAFTR(s) are locacate in central
   aggregation points in the network, such as a core site, the exit
   point from a MAN etc.  As the lwAFTR provides the gateway between the
   IPv6 and IPv4 networks, it allows single stack IPv6 to be deployed in
   the access part of the network.

   In a distributed deployment, lwAFTR function is integrated with the
   BRAS/SR.  Since newly emerging customers might be distributed in the
   whole Metro area, we have to deploy lwAFTR on all BRAS/SRs.  This
   will cost a lot in the initial phase of the IPv6 transition period.
   This model also has the drawback of requiring both IPv4 and IPv6 to
   the BRAS/Service Router devices and so is unsuitable for providers
   wishing to build a single stack IPv6 only core.

4.5.  Path Consistency Consideration

   In Lightweight 4over6, if the binding state is not syncronized among
   multiple lwAFTRs, the lwAFTR in which the subscriber's binding state
   is stored should be exactly the one to service the subscriber.
   Otherwise, there will be no match in the lwAFTR.  This can be
   achieved by using a unique IPv6 tunnel endpoint address and
   corresponding reachable public IPv4 customer prefix for each lwAFTR.

   If multiple lwAFTRs are deployed for resilience or scalability, using
   the top-down provisioning model, all of the lwAFTRs in this cluster
   will share the same IPv6 tunnel endpoint and set of reachable
   prefixes.  In this case, any packet arriving at any of the cluster
   members will be processed in the same way.  However, it is worth
   considering using ECMP with flow-hashing so that a single customer's
   traffic will be processed by the same lwAFTR.  This will reduce the
   change of packet re-ordering.

   In Lightweight 4over6, if the binding state is not syncronized among
   multiple lwAFTRs, the lwAFTR in which the subscriber's binding state
   is stored should be exactly the one to service the subscriber.
   Otherwise, there will be no match in lwAFTR.  This requires the
   provionsion packets (either using DHCPv4-over-DHCPv6 or PCP Port-set)

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   should arrive at the same lwAFTR as the subsquent IP-in-IP traffic.
   If multiple lwAFTRs are using the same Tunnel End Point address and
   there are intermediate routers between lwB4 and lwAFTR, there might
   be a problem when intermediate routers perform ECMP based on L4 hash
   for the plain provionsion packets while doing L3 hash for subsequent
   IP-in-IP traffic.  In this case, it is recommended that the
   provisioning packet is sent over IPv6 tunnel so that intermediate
   routers can only process ECMP using L3 hash.

5.  lwB4 Deployment Considerations

   For the lwB4, the DNS Deployment Considerations and B4 Remote
   Management in [RFC6908] can also be applied here.  In this section,
   only additional considerations relevant to lw4o6 are discussed.

5.1.  NAT Traversal Issues

   In lw4o6, as the subscriber's traffic source port will be restricted
   to the port-set allocated from the provisioning system, there will be
   an impact on some NAT traversal mechanisms.  For example, in UPnP
   1.0, the external port number that can be used by a remote peer is
   selected by a UPnP client in end host.  If the client randomly
   selects a port number which dos not fall in that valid port-set, the
   UPnP process will fail.

   This is likely to happen because an end-host does not have knowledge
   of the port-set which has been allocated to the lwB4.  More detailed
   experimental results can be found in
   [I-D.deng-aplusp-experiment-results].  This problem will not exist in
   UPnP 2.0 because the end-host's UPnP client in the will negotiate the
   external port number with the server.  Another way is to implement a
   mechanism (e.g.  [RFC7753]) in end host to fetch the allocated port-
   set from the lwB4.  The UPnP client can then select the port number
   within the port-set.

5.2.  Static Port Forwarding Configuration

   Currently, some externally initiated applications rely on manual
   configuration to reserve a port in the CPE.  The restricted port-set
   used by the lwB4 may be problematic for manual port forwarding
   configuration.  It is recommended that the port-set allocated from
   the provioning system should be visible to the user (e.g. via the
   configuration interface of a HGW which implements the lwB4 function),
   which can be used as a hint for subscribers to add port forwarding

   It should also be noted that the well-known ports are not generally
   allocated to a lwB4, unless the client is being allocated a full IPv4

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   address with no address sharing ([RFC7596], Section 5.1).  If the
   user wishes to make a service running on an end-host using a well-
   known port externally accessible, it is necessary to configure the
   lwB4's port-forwarding to re-map the well-known port to a port taken
   from the allocated port-set.

6.  DS-Lite Compatibility Consideration

   Lightweight 4over6 can be either deployed as a complete solution, or
   in conjuction with DS-Lite.  Since Lightweight 4over6 does not any
   have extra requirement on IPv6 addressing, it can use use the same
   addressing scheme with DS-Lite, together with routing policy, user
   management policy, etc.  Besides, the bottom-up model has quite
   similar requirement and workflow on the supporting system with DS-
   Lite.  Therefore, it is suitable for operators to deploy
   incrementally in existing DS-Lite network

6.1.  Case 1: Integrated Network Element with Lightweight 4over6 and DS-
      Lite AFTR Scenario

   In this case, DS-Lite has been deployed in the network.  Later in the
   deployment schedule, the operator decided to implement Lightweight
   4over6 lwAFTR function in the same network element (depicted in
   Figure3, below).  Therefore, the same network element needs to
   support both transition mechanisms.

   There are two options to distinguish the traffic from two transition

   The first one is to distinguish using the client's source IPv4
   address.  The IPv4 address from Lightweight 4over6 is public address
   as NAT has been done in the lwB4, and IPv4 address for DS-lite is
   private address as NAT will be done on AFTR.  When the network
   element receives an encapsulated packet, it would de-capsulate packet
   and apply the transition mechanism based on the IPv4 source address
   in the packet.  This requires the network element to examine every
   packet and may introduce significant extra load to the network
   element.  However, both the B4 element and Lightweight 4over6 lwB4
   can use the same DHCPv6 option [RFC6334] with the same FQDN of the
   AFTR and lwAFTR.

   The second one is to distinguish using the destination's tunnel IPv6
   address.  One network element can run separated instances for
   Lightweight 4over6 and DS-Lite with different tunnel addresses.  Then
   B4 element and Lightweight 4over6 lwB4 can use the same DHCPv6 option
   [RFC6334] with different FQDNs pointing to corresponding tunnel
   addresses.  This requires the supporting system should distinguish
   different types of users when assigning the FQDNs in DHCPv6 process.

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   Another option is to use a new DHCPv6 option [RFC7598] to discover
   the lwAFTR's FQDN.

                    +               |              |
+---------+  +------+---+        +--+--+           |
|  Host   |  | LW 4over6|        |     |           |
|         |--|   lwB4   | ======-| BNG | === +-------------+   +-----------+
+---------+  +----------+        +--|--+     |LW 4over6    |   |   IPv4    |
                                             |lwAFTR/      |---| Internet  |
+---------+  +------+---+        +--+--+     |DS-Lite AFTR |   |           |
|  Host   |--| DS-Lite  | =======|     | ====+-------------+   +-----------+
|         |  |    B4    |        | BNG |           |
+---------+  +----------+        +--|--+           |
                    +               |              |

        Figure 3 DS-Lite Coexistence scenario with Integrated AFTR

6.2.  Case 2: DS-Lite Coexistent scenario with Separated AFTR

   This is similar to Case 1.  The difference is the lwAFTR and AFTR
   functions won't be co-located in the same network element (depicted
   in Figure4).  This use case decouples the functions to allow more
   flexible deployment.  For example, an operator may deploy AFTR closer
   to the edge and lwAFTR closer to the core.  Moreover, it does not
   require the network element to pre-configure with the CPE's IPv6
   addresses.  An operator can deploy more AFTR and lwAFTR at needed.
   However, this requires the B4 and lwB4 to discover the corresponding
   network element.  In this case, B4 element and Lightweight 4over6
   lwB4 can still use [RFC6334] with different FQDNs pointing to
   corresponding tunnel end-point addresses, and the supporting system
   should distinguish different types of users.

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                    |                  |                 |
+---------+  +------+---+       +------+-----+           |
|  Host   |__| LW 4over6|       |    BNG     |           |
|         |  |   lwB4   |=======|DS-Lite AFTR|=====+------------+   +----------+
+---------+  +----------+       +------+-----+     |   lw4o6    |   |   IPv4   |
                                                   |   lwAFTR   |---| Internet |
+---------+  +------+---+       +------+-----+     |            |   |          |
|  Host   |__|  DS-Lite |=======|    BNG     |=====+------------+   +----------+
|         |  |    B4    |       |DS-Lite AFTR|           |
+---------+  +----------+       +------+-----+           |
                    |                  |                 |

     Figure 4 DS-Lite Co-existence scenario with Seperated AFTR/lwAFTR

7.  Acknowledgements


8.  References

              Bajko, G., Savolainen, T., Boucadair, M., and P. Levis,
              "Port Restricted IP Address Assignment", draft-bajko-
              pripaddrassign-04 (work in progress), April 2012.

              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-11
              (work in progress), February 2013.

              Deng, X., Boucadair, M., and F. Telecom, "Implementing A+P
              in the provider's IPv6-only network", draft-deng-aplusp-
              experiment-results-00 (work in progress), March 2011.

              Sivakumar, S. and R. Penno, "IPFIX Information Elements
              for logging NAT Events", draft-ietf-behave-ipfix-nat-
              logging-13 (work in progress), January 2017.

              Chen, Z., Zhou, C., Tsou, T., and T. Taylor, "Syslog
              Format for NAT Logging", draft-ietf-behave-syslog-nat-
              logging-06 (work in progress), January 2014.

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              Farrer, I., Sun, Q., Cui, Y., and L. Sun, "DHCPv4 over
              DHCPv6 Source Address Option", draft-ietf-dhc-dhcp4o6-
              saddr-opt-00 (work in progress), March 2017.

              Wing, D., Cheshire, S., Boucadair, M., Penno, R., and P.
              Selkirk, "Port Control Protocol (PCP)", draft-ietf-pcp-
              base-29 (work in progress), November 2012.

              Lee, Y., Maglione, R., Williams, C., Jacquenet, C., and M.
              Boucadair, "Deployment Considerations for Dual-Stack
              Lite", draft-ietf-softwire-dslite-deployment-08 (work in
              progress), January 2013.

              Jiang, S., Fu, Y., Liu, B., Deacon, P., Xie, C., and T.
              Li, "RADIUS Attribute for Softwire Address plus Port based
              Mechanisms", draft-ietf-softwire-map-radius-12 (work in
              progress), May 2017.

              Sun, Q., Wang, H., Cui, Y., Farrer, I., Zoric, S.,
              Boucadair, M., and R. Asati, "A YANG Data Model for IPv4-
              in-IPv6 Softwires", draft-ietf-softwire-yang-01 (work in
              progress), October 2016.

              Lee, Y., Qiong, Q., and C. Liu, "Simple Failover Mechanism
              for Lightweight 4over6", draft-lee-softwire-
              lw4over6-failover-01 (work in progress), July 2013.

              Xie, C., Qiong, Q., Lee, Y., Tsou, T., and P. Wu, "Dynamic
              Host Configuration Protocol for IPv6 (DHCPv6) Option for
              Lightweight 4over6", draft-sun-softwire-lw4over6-dhcpv6-00
              (work in progress), July 2013.

              Zhou, C., Taylor, T., Qiong, Q., and M. Boucadair,
              "Attribute-Value Pairs For Provisioning Customer Equipment
              Supporting IPv4-Over-IPv6 Transitional Solutions", draft-
              zhou-dime-4over6-provisioning-05 (work in progress),
              September 2014.

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   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,

   [RFC6052]  Bao, C., Huitema, C., Bagnulo, M., Boucadair, M., and X.
              Li, "IPv6 Addressing of IPv4/IPv6 Translators", RFC 6052,
              DOI 10.17487/RFC6052, October 2010,

   [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,

   [RFC6333]  Durand, A., Droms, R., Woodyatt, J., and Y. Lee, "Dual-
              Stack Lite Broadband Deployments Following IPv4
              Exhaustion", RFC 6333, DOI 10.17487/RFC6333, August 2011,

   [RFC6334]  Hankins, D. and T. Mrugalski, "Dynamic Host Configuration
              Protocol for IPv6 (DHCPv6) Option for Dual-Stack Lite",
              RFC 6334, DOI 10.17487/RFC6334, August 2011,

   [RFC6346]  Bush, R., Ed., "The Address plus Port (A+P) Approach to
              the IPv4 Address Shortage", RFC 6346,
              DOI 10.17487/RFC6346, August 2011,

   [RFC6431]  Boucadair, M., Levis, P., Bajko, G., Savolainen, T., and
              T. Tsou, "Huawei Port Range Configuration Options for PPP
              IP Control Protocol (IPCP)", RFC 6431,
              DOI 10.17487/RFC6431, November 2011,

   [RFC6908]  Lee, Y., Maglione, R., Williams, C., Jacquenet, C., and M.
              Boucadair, "Deployment Considerations for Dual-Stack
              Lite", RFC 6908, DOI 10.17487/RFC6908, March 2013,

   [RFC7040]  Cui, Y., Wu, J., Wu, P., Vautrin, O., and Y. Lee, "Public
              IPv4-over-IPv6 Access Network", RFC 7040,
              DOI 10.17487/RFC7040, November 2013,

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   [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, <>.

   [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,

   [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,

   [RFC7600]  Despres, R., Jiang, S., Ed., Penno, R., Lee, Y., Chen, G.,
              and M. Chen, "IPv4 Residual Deployment via IPv6 - A
              Stateless Solution (4rd)", RFC 7600, DOI 10.17487/RFC7600,
              July 2015, <>.

   [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,

   [RFC7753]  Sun, Q., Boucadair, M., Sivakumar, S., Zhou, C., Tsou, T.,
              and S. Perreault, "Port Control Protocol (PCP) Extension
              for Port-Set Allocation", RFC 7753, DOI 10.17487/RFC7753,
              February 2016, <>.

Appendix A.  China Telecom Experimental Results

   We have deployed Lightweight 4over6 in our operational network of
   HuNan province, China.  It is designed for broadband access network,
   and different versions of the lwB4 function have been implemented
   including a Linksys device, a software client for Windows XP, Windows
   Vista and Windows 7.

   It can be integrated with existing dial-up mechanisms such as PPPoE,
   etc.  The major objectives listed below aimed to verify the
   functionality and performance of Lightweight 4over6:

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   o  Verify how to deploy Lightweight 4over6 in a practical network.

   o  Verify the impact of applications with Lightweight 4over6.

   o  Verify the performance of Lightweight 4over6.

A.1.  Experimental Environment

   The network topology for this experiment is depicted in Figure 5.

+-----+  +-------+                           | Syslog |
|Host1+--+lwB4   |----+                      | Server |
+-----+  +-------+    |                      +---+----+     ---------
                      |         /------\         |        //         \\
                      |        //      \\        |       /             \
+-----+  +-------+    +-+--+  |   IPv6   |   +---+----+ |               |
|Host2+--|lwB4   |----+BRAS+--|  Network |---|lwAFTR  +-+ IPv4 Internet +
+-----+  +-------+    +-+--+   \\      //    +--------+ |               |
                      |         \--+---/    (PCP Server) \             /
                      |            |                      \\         //
+-----+  +-------+    |            |                        ---------
|Host3+--+lwB4   +----+            |
+-----+  +-------+                 |                        ---------
                                   |                      //         \\
                                   |                     /             \
                                                           |                    |               |
                                   +--------------------+ IPv6 Internet +
                                                        |               |
                                                         \             /
                                                          \\         //

       Figure 5 China Telecom Lightweight 4over6 Experiment Topology

   In this deployment model, the lwAFTR is co-located with an extended
   PCP server to assign port-restricted IPv4 addresses and port-sets to
   lwB4s.  It also triggers subscriber-based logging event to a
   centrilized syslog server.  IPv6 address pools for subscribers have
   been distributed to BRASs for configuration, while the available
   public IPv4 address pools are configured by the centralized lwAFTR
   with a default address sharing ratio.  It is rather flexible for IPv6
   addressing and routing, and there is little impact on existing IPv6

   In our experiment, lwB4 will firstly get its IPv6 address and
   delegated prefix through PPPoE, and then initiate a PCP-extended
   request to get public IPv4 address and its valid port set.  The

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   lwAFTR will thus create a subscriber-based state accordingly, and
   notify the syslog server with {IPv6 address, IPv4 address, port set,

A.2.  Experimental Results

   In our trial, we mainly focused on application and performance tests.
   The applications tested include web (HTTP/HTTPS), email, instant
   messaging, FTP, telnet, SSH, video, Video Camera, P2P, online gaming,
   and VoIP.

   For the performance tests, we measured the number of concurrent
   session and throughput performance.

   The experimental results are listed as follows:

   |  Application Type  |   Test Result        |Port Number Occupation |
   |   Web              |         OK           | normal websites: 10~20|
   |                    | IE, Firefox, Chrome  | Ajex Flash webs: 30~40|
   |   Video            |   ok, web based or   |      30~40            |
   |                    |   client based       |                       |
   |   Instant Message  |         OK           |                       |
   |                    | QQ, MSN, gtalk, skype|       8~20            |
   |   P2P              |         OK           | lower speed: 20~600   |
   |                    |utorrent,emule,xunlei | (per seed)            |
   |                    |                      | higher speed: 150~300 |
   |   FTP              | need ALG for active  |       2               |
   |                    |  mode, flashxp       |                       |
   |   SSH, TELNET      |         OK           |1 for SSH, 3 for telnet|
   |   online game      | OK for QQ, flash game|    20~40              |

       Figure 6 China Telecom Lightweight 4over6 Experiment Results

   The performance tests for the lwAFTR are taken using a PC.  Due to
   limitations of the PC hardware, the overall throughput is limited to
   around 800 Mbps.  However, it can still support more than one hundred
   million concurrent sessions.

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A.3.  Conclusions

   From the experiment, we reached the following conclusions:

   o  Lightweight 4over6 has good scalability.  As it is a lightweight
      solution that only maintains per-subscription state information,
      it can easily support a large amount of concurrent subscribers.

   o  Lightweight 4over6 can be deployed rapidly.  No modifications to
      the existing addressing and routing system in our operational
      network was necessary.  Logging of customer address allocations
      was easy to implement.

   o  Lightweight 4over6 can support the majority of current IPv4
      applications commonly in use.

Appendix B.  Tsinghua University Experimental Result

   Lightweight 4over6 has been deployed in the campus of Tsinghua
   University, China.  DHCPv4o6 [RFC7341] is used for dynamically
   provisioning the lwB4's IPv4 address and port set [RFC7618].
   Wireless APs for Lightweight 4over6, were deployed, covering a large
   portion of the campus, allowing mobile devices to connect to the
   lwB4.  We also deployed a lwB4 gateway in some of our buildings so
   that end device could connect directly to the lwB4.  Users access the
   IPv4 Internet through the China Next Generation Internet (CNGI) IPv6

B.1.  Experimental Environment

   The network topology for this experiment is depicted in Figure 7.

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+-----+                        -------                       ---------
|Host1+---+                   /         \                   //         \\
+-----+   |                  //         \\                 /             \
+-----+   |  +--------+     |  CNGI IPv6  |  +--------+   |               |
|Host2+---+--+lwB4(AP)+--+--|   Network   |--+ lwAFTR +---+ IPv4 Internet +
+-----+   |  +--------+  |   \\         //   +--------+   |               |
+-----+   |              |    \         / (DHCP4o6 Server) \             /
|Host3+---+              |      --+----                     \\         //
+-----+                  |        |                           ---------
                         |        |
+-----+                  |        |                           ---------
|Host4+---+              |        |                         //         \\
+-----+   |   +------+   |        |                        /             \
          +---+lwB4  +---+        |                       |               |
+-----+   |   +------+            +-----------------------+ IPv6 Internet +
|Host5+---+                                               |               |
+-----+                                                    \             /
                                                            \\         //

    Figure 7 Tsinghua University Lightweight 4over6 Experiment Topology

   In this deployment model, the lwAFTR is co-located with a DHCP4o6
   server to assign port-restricted IPv4 addresses and port-sets to the
   lwB4.  The lwAFTR snoops the DHCPv4 over DHCPv6 messages generated or
   received by the DHCP4o6 server and updates its binding table

   In our experiment, the lwB4 receives its IPv6 address through static
   or dynamic configuration.  It then sends a DHCP4o6 request to the
   lwAFTR device to get the public IPv4 address and valid port-set.  The
   lwAFTR will add the IPv6 address, IPv4 address, and port-set
   information of the lwB4 into its binding table.

B.2.  Experimental Results

   In the Tsinghua University experiment, the performance of various
   applications were tested including web (HTTP/HTTPS), email, instant
   messaging, FTP, telnet, SSH, video, Video Camera, P2P, online gaming,
   and VoIP.  We also tested different terminal devices including PC/
   laptop computers, and cell phone.  These devices used different
   operating systems, including Windows 7, MacOS, Android, and Apple

   The experimental results were as follows:

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|Application Type | Test Applications      | Test Subjects       |Result|
| Web             | IE, Chrome, Sougou     |Browse websites,     |  OK  |
|                 |                        |download files       |      |
| Video           | Youku, pptv, qqlive    |VOD, live video      |  OK  |
|                 |(Web based,client based)|                     |      |
| P2P             | Bittorrent, xunlei     |Download files       |  OK  |
| Ping/tracert    | Command line           |Ping/tracert URL     |  OK  |
| TELNET/SSH      | Putty, secureCRT       |Telnet/SSH login     |  OK  |
| Email           | 126, QQ, hotmail       |Send/receive email   |  OK  |
|                 |(Web based,client based)|                     |      |
| Cloud storage   | Baidu Cloud            |Upload/download files|  OK  |
|Instant messaging| Skype, QQ              |Send/receive messages|  OK  |
|Online gaming    | QQ game                |Enter game           |  OK  |
|Online payment   | JD, Taobao             |Complete payment     |  OK  |

    Figure 8 Tsinghua University Lightweight 4over6 experimental result

B.3.  Conclusion

   Lightweight 4over6 supports the majority of current IPv4 applications
   and services.  The user experience of using Lightweight 4over6 is no
   different from using the native IPv4 network.  It can satisfy the
   IPv4 network service demands of IPv6 network users.

Authors' Addresses

   Qiong Sun
   China Telecom
   Room 708, No.118, Xizhimennei Street
   Beijing  100035

   Phone: +86-10-58552936>

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   Chongfeng Xie
   China Telecom
   Room 708, No.118, Xizhimennei Street
   Beijing  100035

   Phone: +86-10-58552116>

   Yiu L. Lee
   One Comcast Center
   Philadelphia, PA  19103


   Maoke Chen
   FreeBit Co., Ltd.
   13F E-space Tower, Maruyama-cho 3-6
   Shibuya-ku, Tokyo  150-0044


   Tianxiang Li
   Tsinghua University
   Beijing  100084

   Phone: +86-10-6278-5822

   Ian Farrer
   Deutsche Telekom AG
   Bonn  53227


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