path: root/doc/rfc/rfc6908.txt

Internet Engineering Task Force (IETF)                            Y. Lee
Request for Comments: 6908                                       Comcast
Category: Informational                                      R. Maglione
ISSN: 2070-1721                                            Cisco Systems
                                                             C. Williams
                                                               MCSR Labs
                                                            C. Jacquenet
                                                            M. Boucadair
                                                          France Telecom
                                                              March 2013


             Deployment Considerations for Dual-Stack Lite

Abstract

   This document discusses the deployment issues of and the requirements
   for the deployment and operation of Dual-Stack Lite (DS-Lite).  This
   document describes the various deployment considerations and
   applicability of the DS-Lite architecture.

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for informational purposes.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Not all documents
   approved by the IESG are a candidate for any level of Internet
   Standard; see Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc6908.















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Copyright Notice

   Copyright (c) 2013 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
   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. Overview ........................................................3
   2. AFTR Deployment Considerations ..................................3
      2.1. Interface Consideration ....................................3
      2.2. MTU and Fragmentation Considerations .......................4
      2.3. Logging at the AFTR ........................................4
      2.4. Blacklisting a Shared IPv4 Address .........................5
      2.5. AFTR's Policies ............................................5
           2.5.1. Outgoing Policy .....................................5
           2.5.2. Incoming Policy .....................................6
      2.6. AFTR Impacts on Accounting Process .........................6
      2.7. Reliability Considerations of AFTR .........................7
      2.8. Strategic Placement of AFTR ................................8
      2.9. AFTR Considerations for Geographically Aware Services ......8
      2.10. Impacts on QoS Policy .....................................9
      2.11. Port Forwarding Considerations ............................9
      2.12. DS-Lite Tunnel Security ..................................10
      2.13. IPv6-Only Network Considerations .........................10
   3. B4 Deployment Considerations ...................................10
      3.1. DNS Deployment Considerations .............................11
      3.2. IPv4 Service Monitoring ...................................11
           3.2.1. B4 Remote Management ...............................11
           3.2.2. IPv4 Connectivity Check ............................11
   4. Security Considerations ........................................12
   5. Acknowledgements ...............................................12
   6. References .....................................................12
      6.1. Normative References ......................................12
      6.2. Informative References ....................................12







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1.  Overview

   DS-Lite [RFC6333] is a transition technique that enables operators to
   multiplex public IPv4 addresses while provisioning only IPv6 to
   users.  DS-Lite is designed to continue offering IPv4 services while
   operators upgrade their networks incrementally to IPv6.  DS-Lite
   combines IPv4-in-IPv6 softwire [RFC2473] and Network Address
   Translator IPv4/IPv4 (NAT44) [RFC3022] to enable more than one user
   to share a public IPv4 address.

   While Appendix A of [RFC6333] explains how to deploy DS-Lite within
   specific scenarios, the purpose of this document is to describe
   problems that arise when deploying DS-Lite and what guidance should
   be taken to mitigate those issues.  The information is based on real
   deployment experience and is compiled in one comprehensive document
   so that operators aren't required to search through various RFCs
   deciding which sections are applicable and impact their DS-Lite
   deployment.

2.  AFTR Deployment Considerations

2.1.  Interface Consideration

   Address Family Transition Router (AFTR) is a network element that is
   deployed inside the operator's network.  An AFTR can be a stand-alone
   device or be embedded into a router.  The AFTR is the IPv4-in-IPv6
   tunnel termination point and the NAT44 device.  It is deployed at the
   IPv4-IPv6 network border where the tunnel interface is IPv6 and the
   external NAT44 interface is IPv4.  The Basic Bridging BroadBand (B4)
   element [RFC6333] is a function implemented on a dual-stack-capable
   node (either a host device or a home gateway) that creates a tunnel
   to an AFTR.  Although an operator can configure both softwire tunnel
   termination and interface for NAT44 functions on a single physical
   interface (yet, keep them logically separated), there are scenarios
   we recommend to configure two individual interfaces (i.e., one
   dedicated for IPv4 and one dedicated for IPv6) to segregate the
   functions.

   o  The access network between the B4 and AFTR is an IPv6-only
      network, and the network between the AFTR and IPv4 network is an
      IPv4-only network.  In this deployment scenario, the AFTR
      interface to the IPv6-only network and the interface to the IPv4
      network should use two physical interfaces on the AFTR.

   o  Operators may use Operations Support System (OSS) tools (e.g.,
      Multi Router Traffic Grapher) to collect interface data packet
      count information.  If an operator wants to separate the softwire
      function and NAT44 function on different physical interfaces for



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      collecting a data packet count, and the AFTR does not support
      packet count for logical interfaces, they should use two physical
      interfaces on the AFTR.

2.2.  MTU and Fragmentation Considerations

   DS-Lite is part tunneling protocol.  Tunneling introduces overhead to
   the packet and decreases the effective MTU size after encapsulation.
   DS-Lite users may experience problems with applications such as not
   being able to download Internet pages or transfer large files.

   Since fragmentation and reassembly is not optimal, the operator
   should do everything possible to eliminate the need for it.  If the
   operator uses simple IPv4-in-IPv6 softwire [RFC2473], it is
   recommended that the MTU size of the IPv6 network between the B4 and
   the AFTR accounts for the additional overhead (40 bytes).  If the
   access network MTU size is fixed and cannot be changed, the operator
   should be aware that the B4 and the AFTR must support fragmentation
   as defined in [RFC6333].  The operator should also be aware that
   reassembly at the Tunnel Exit-Point is resource intensive as a large
   number of B4 may terminate on the same AFTR.  Scalability of the AFTR
   is advised in this scenario.

2.3.  Logging at the AFTR

   A source-specific log is essential for backtracking specific hosts
   when a problem is identified with one of the AFTR's NAT-ed addresses.
   The source-specific log contains the B4 IPv6 source address,
   transport protocol, source port, and source IPv4 address after it has
   been NAT-ed.  Using the source-specific log, operators can uniquely
   identify a specific host when a DS-Lite host experiences problems
   accessing the IPv4 network.  To maximize IPv4 shared ratio, an
   operator may configure a short timeout value for NAT44 entries.  This
   will result in a large number of logs created by the AFTR.  For
   operators who desire to aggregate the logs, they can configure the
   AFTR to preallocate a range of ports to each B4.  This range of ports
   will be used in the NAT44 function, and the AFTR will create one log
   entry for the whole port range.  This aggregation can significantly
   reduce the log size for source-specific logging.

   Some operators may require logging both source and destination
   information for a host's connections.  This is called a destination-
   specific log.  A destination-specific log contains the B4's IPv6
   address, transport protocol, source port, source IPv4 address after
   it has been NAT-ed, destination port, and destination IPv4 address.
   A destination-specific log is session-based; the operators should be
   aware that they will not be able to aggregate log entries.  When
   using a destination-specific log, the operator must be careful of the



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   large number of log entries created by the AFTR.  Some AFTR
   implementations may keep the logs in their main memory.  This may be
   CPU and memory resource intensive.  The operators should configure
   the AFTR to periodically send logs to storage facility and then purge
   them from the AFTR.

2.4.  Blacklisting a Shared IPv4 Address

   The AFTR is a NAT device.  It enables multiple B4s to share a single
   public IPv4 address.  [RFC6269] discusses some considerations when
   sharing an IPv4 address.  When a public IPv4 address is blacklisted
   by a remote peer, this may affect multiple users or hosts.  Operators
   deploying DS-Lite should be aware that Internet hosts may not be
   aware that a given single IPv4 address is actually shared by multiple
   B4s.  A content provider might block services for a shared IPv4
   address and this would then impact all B4s sharing this particular
   IPv4 address.  The operator would be likely to receive calls related
   to service outage and would then need to take appropriate corrective
   actions.  [RFC6302] describes necessary information required to
   identify a user or host in shared address environment.  It is also
   worth mention that [NAT-REVEAL] analyses different approaches to
   identify a user or host in a shared address environment.

2.5.  AFTR's Policies

   There are two types of AFTR policies:

   o  Outgoing Policies apply to packets originating from B4 to the
      AFTR.  These policies should be provisioned on the AFTR's IPv6
      interface that is connected to the B4s.

   o  Incoming Policies apply to packets originating from IPv4 networks
      to B4s.  These policies should be provisioned on the IPv4
      interface connected to the IPv4 network.

2.5.1.  Outgoing Policy

   Outgoing Policies may include Access Control List (ACL) and Quality
   of Service (QoS) settings.  These policies control the packets from
   B4s to the AFTR.  For example, the operator may configure the AFTR
   only to accept B4 connections that originated from specific IPv6
   prefixes configured in the AFTR.  More discussion of this use case
   can be found in Section 2.12.  An operator may configure the AFTR to
   give priority to the packets marked by certain Differentiated
   Services Code Point (DSCP) values [RFC2475].  Furthermore, an AFTR
   may also apply an Outgoing Policy to limit the rate of port
   allocation for a single B4's IPv6 address.




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   Some operators offer different service level agreements (SLAs) to
   users to meet their requirements.  Some users may require more ports
   and some may require different service priority.  In this deployment
   scenario, the operator can implement Outgoing Policies specified to a
   user's B4 or a group of B4s sharing the same policies.

2.5.2.  Incoming Policy

   Similar to the Outgoing Policy, an Incoming Policy may also include
   ACL and QoS settings.  The Outgoing Policy controls packets coming
   from the IPv4 network to the B4s.  Incoming packets are normally
   treated equally, so these policies are globally applied.  For
   example, an operator wants to use a predefined DSCP value to signal
   the IPv6 access network to apply certain traffic policies.  In this
   deployment scenario, the operator can configure the AFTR to mark the
   incoming packets with the predefined DSCP value.  This policy will
   apply to all incoming packets from the IPv4 network.

2.6.  AFTR Impacts on Accounting Process

   This section discusses IPv4 and IPv6 traffic accounting in the
   DS-Lite environment.  In a typical broadband access scenario (e.g.,
   DSL or Cable), the B4 is embedded in a Residential Gateway.  The edge
   router for the B4s in the provider's network is an IPv6 edge router.
   The edge router is usually responsible for IPv6 accounting and the
   user management functions such as authentication, authorization, and
   accounting (AAA).  However, given the fact that IPv4 traffic is
   encapsulated in an IPv6 packet at the B4 and only decapsulated at the
   AFTR, the edge router will require additional functionality to
   associate IPv4 accounting information to the B4 IPv6 address.  If
   DS-Lite is the only application using the IPv4-in-IPv6 protocol in
   the IPv6 access network, the operator can configure the edge router
   to check the IPv6 Next Header field in the IPv6 header, identify the
   protocol type (i.e., 0x04), and collect IPv4 accounting information.

   Alternatively, the AFTR may perform accounting for IPv4 traffic.
   However, operators must be aware that this will introduce some
   challenges, especially in DSL deployment.  In DSL deployment, the AAA
   transaction normally happens between the edge router (i.e., Broadband
   Network Gateway) and AAA server.  [RFC6333] does not require the AFTR
   to interact with the AAA server or edge router.  Thus, the AFTR may
   not have the AAA parameters (e.g., Account Session ID) associated
   with B4s to generate an IPv4 accounting record.  IPv4 traffic
   accounting at the AFTR is not recommended when the AAA parameters
   necessary to generate complete IPv4 accounting records are not
   available.  The accounting process at the AFTR is only necessary if
   the operator requires separating per-B4 accounting records for IPv4
   and IPv6 traffic.  If the per-B4 IPv6 accounting records, collected



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   by the edge router, are sufficient, then the additional complexity of
   enabling IPv4 accounting at the AFTR is not required.  It is
   important to notice that, since the IPv4 traffic is encapsulated in
   IPv6 packets, the data collected by the edge router for IPv6 traffic
   already contains the total amount of traffic (i.e., IPv4 and IPv6).

   Even if detailed accounting records collection for IPv4 traffic may
   not be required, it would be useful for an operator, in some
   scenarios, to have information that the edge router generates for the
   IPv6 traffic.  This information can be used to identify the AFTR who
   is handling the IPv4 traffic for that B4.  This can be achieved by
   adding additional information to the IPv6 accounting records.  For
   example, operators can use RADIUS attribute information specified in
   [RFC6519] or a new attribute to be specified in Internet Protocol
   Detailed Record (IPDR).

2.7.  Reliability Considerations of AFTR

   For robustness, reliability, and load distribution purposes,
   operators may deploy multiple AFTRs.  In such cases, the IPv6
   prefixes and algorithm to build the tunneling mechanisms configured
   on each of these AFTRs will be the same.  In [RFC6333], Appendix A.3
   mentions that High Availability (HA) is the operator's
   responsibility.  Since DS-Lite is a stateful mechanism, all
   requirements for load-balancing and failover mechanisms apply.  There
   are many ways to implement HA in a stateful mechanism; the most
   common are Cold Standby mode and Hot Standby mode.  More discussion
   on deploying these two modes for NAT can be found in [NAT-STANDBY].
   In Cold Standby mode, the AFTR states are not replicated from the
   Primary AFTR to the Backup AFTR.  When the Primary AFTR fails, all
   the existing established sessions will be flushed out.  The internal
   hosts are required to reestablish sessions with the external hosts.
   In Hot Standby mode, the session's states are replicated on-the-fly
   from the Primary AFTR to the Backup AFTR.  When the Primary AFTR
   fails, the Backup AFTR will take over all the existing established
   sessions.  In this mode, the internal hosts are not required to
   reestablish sessions with the external hosts.

   For operators, the decision to use Cold Standby mode or Hot Standby
   mode depends on the trade-off between capital cost and operational
   cost.  Cold Standby mode does not require a Backup Standby AFTR to
   synchronize session states.  This simplifies the operational model.
   When the Primary AFTR goes down, any AFTR with extra capacity can
   take over.  Hot Standby mode provides a smoother failover experience
   to users; the cost for the operators is more careful failover
   planning.  For most deployment scenarios, we believe that Cold
   Standby mode should be sufficient enough and is thus recommended.




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2.8.  Strategic Placement of AFTR

   In the DS-Lite environment, the AFTR is the logical next-hop router
   of the B4s to access the IPv4 network, so the placement of the AFTR
   will affect the traffic flows in the access network and overall
   network design.  In general, there are two placement models to deploy
   an AFTR.  Model One deploys the AFTR at the edge of the network to
   cover a small region.  Model Two deploys the AFTR at the core of the
   network to cover a large region.

   When an operator considers where to deploy the AFTR, the operator
   must make trade-offs.  The AFTR in Model One serves fewer B4s; thus,
   it requires a less powerful AFTR.  Moreover, the traffic flows are
   more evenly distributed to the AFTRs.  However, it requires deploying
   more AFTRs to cover the entire network.  Often, the operation cost
   increases proportionally with the amount of network equipment.

   The AFTR in Model Two covers a larger area; thus, it serves more B4s.
   The operator could deploy only a few AFTRs to support the entire user
   base.  However, this model requires a more powerful AFTR to sustain
   the load at peak hours.  Since the AFTR would support B4s from
   different regions, the AFTR would be deployed closer to the core
   network.

   DS-Lite framework can be incrementally deployed.  An operator may
   consider starting with Model Two.  When the demand increases, the
   operator can push the AFTR closer to the edge, which would
   effectively become Model One.

2.9.  AFTR Considerations for Geographically Aware Services

   By centralizing public IPv4 addresses in the AFTR, remote services
   can no longer rely on an IPv4 address and IPv4 routing information to
   derive a host's geographical information.  For example, the IPv6
   access network and the AFTR may be in two different cities.  If the
   remote services rely on the IPv4 address to locate a host, they may
   have thought the host was in a different city.  [RFC6269] Section 7
   describes the problem in more detail.  Applications could explicitly
   ask users to enter location information, such as postal code or
   telephone number, before offering geographical service.  In contrast,
   applications could use HTTP-Enabled Location Delivery (HELD)
   [RFC5985] to get the location information from the Location
   Information Server and give this information to the remote peer.
   [RFC6280] describes an architecture to enable location-based
   services.  However, to mitigate the impact, we recommend that
   operators deploy the AFTR as close to B4s as possible.





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2.10.  Impacts on QoS Policy

   This section describes the application of [RFC2983] to the DS-Lite
   deployment model.  Operators must ensure that the QoS policy that is
   in place operates properly within the DS-Lite deployment.  In this
   regard, operators commonly use DSCP [RFC2475] to classify and
   prioritize different types of traffic in their networks.  DS-Lite
   tunnel can be seen as a particular case of uniform conceptual tunnel
   model, as described in Section 3.1 of [RFC2983].  The uniform model
   views an IP tunnel only as a necessary mechanism to forward traffic
   to its destination: the tunnel has no significant impact on traffic
   conditioning.  In this model, any packet has exactly one DSCP field
   that is used for traffic conditioning at any point, and it is the
   field in the outermost IP header.  In the DS-Lite model, this is the
   Traffic Class field in the IPv6 header.  According to [RFC2983],
   implementations of this model copy the DSCP value to the outer IP
   header at encapsulation and copy the outer header's DSCP value to the
   inner IP header at decapsulation.

   Operators should use this model by provisioning the network such that
   the AFTR copies the DSCP value in the IPv4 header to the Traffic
   Class field in the IPv6 header, after the encapsulation for the
   downstream traffic.  Similarly, the B4 copies the DSCP value in the
   IPv4 header to the Traffic Class field to the IPv6 header, after the
   encapsulation for the upstream traffic.  Traffic identification and
   classification can be done by examining the outer IPv6 header in the
   IPv6 access network.

2.11.  Port Forwarding Considerations

   Some applications behind the B4 require the B4 to accept incoming
   requests.  If the remote application wants to communicate to the
   application behind the B4, the remote application must know both the
   NAT-ed IPv4 address used by the B4 and the IPv4 destination port.
   Some applications use Universal Plug and Play (UPnP) (e.g., popular
   gaming consoles) or Interactive Community Establishment (ICE)
   [RFC5245] to request incoming ports.  Some applications rely on
   Application Level Gateway (ALG) or manual port configuration to
   reserve a port in the NAT.  For the DS-Lite deployment scenario
   whereby the B4 does not own a full IPv4 address, the operator will
   manage port-forwarding in the serving AFTR.  Operators may use Port
   Control Protocol (PCP) [PCP-BASE] as guidance to provide port
   forwarding service.  Operators will deploy PCP client in the B4s.
   PCP permits the PCP server to be deployed in a stand-alone server.
   However, we recommend that operators consider deploying the PCP
   server in the AFTR.  This will ease the overhead to design a global
   configuration for the PCP server for many AFTRs because each PCP
   server will be dedicated to the collocated AFTR.



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   When sharing an IPv4 address, not all of the ports are available to a
   B4.  Some restricted ports (i.e., 0-1023) are well known such as TCP
   port 25 and 80.  Many users may want to be provisioned with the
   restricted ports.  For fairness, we recommend that operators
   configure the AFTR and not allocate the restricted ports to regular
   DS-Lite B4s.  This operation model ensures that DS-Lite B4s will have
   uniform configuration, which can simplify provisioning and operation.
   For users who want to use the restricted ports, operators can
   consider provisioning a full IPv4 address to those users' B4s.  If an
   operator still wants to provision restricted ports to specific B4s,
   it may require implementing a static B4's configuration in the AFTR
   to match the B4's IPv6 address to the NAT rules.  Alternatively, the
   B4 may dynamically allocate the ports, and the AFTR authenticates the
   session's request using PCP [PCP-BASE].

2.12.  DS-Lite Tunnel Security

   [RFC6333], Section 11 describes security issues associated with the
   DS-Lite mechanism.  To restrict the service offered by the AFTR only
   to registered B4s, an operator can implement the Outgoing Policy on
   the AFTR's tunnel interface to accept only the IPv6 prefixes defined
   in the policy.  For static provisioning, the operator will need to
   know in advance the IPv6 prefixes provisioned to the B4s for the
   softwire in order to configure the policy.  To simplify operation,
   operators should configure the AFTRs in the same region with the same
   IPv6 prefixes' Outgoing Policy.  The AFTRs will accept both regular
   connections and failover connections from the B4s in the same service
   region.

2.13.  IPv6-Only Network Considerations

   In environments where the operator wants to deploy the AFTR in an
   IPv6-only network, the AFTR nodes may not have direct IPv4
   connectivity.  In this scenario, the operator extends the IPv6-only
   boundary to the border of the network and only the border routers
   have IPv4 connectivity.  For both scalability and performance
   purposes, the AFTR is located in the IPv6-only network closer to B4s.
   In this scenario, the AFTR has only IPv6 connectivity and must be
   able to send and receive IPv4 packets.  Enhancements to the DS-Lite
   AFTR are required to achieve this.  [DS-LITE] describes such issues
   and enhancements to DS-Lite in IPv6-only deployments.

3.  B4 Deployment Considerations

   In order to configure the IPv4-in-IPv6 tunnel, the B4 needs the IPv6
   address of the AFTR.  This IPv6 address can be configured using a
   variety of methods ranging from an out-of-band mechanism, manual
   configuration, and DHCPv6 option to RADIUS.  If an operator uses



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   DHCPv6 to provision the B4, the B4 must implement the DHCPv6 option
   defined in [RFC6334].  If an operator uses RADIUS to provision the
   B4, the B4 must implement [RFC6519].

3.1.  DNS Deployment Considerations

   [RFC6333] recommends that the B4 send DNS queries to an external
   recursive resolver over IPv6.  The B4 should implement a proxy
   resolver that will proxy a DNS query from IPv4 transport to the DNS
   server in the IPv6 network.  [RFC6333] does not describe the DNS
   proxy behavior.  In deployment, the operator must ensure that the DNS
   proxy implementation must follow [RFC5625].  This is important
   especially for operators who have deployed, or will consider
   deploying, DNSSEC [RFC4035].

   Some operators may want to give hosts behind the B4 an IPv4 address
   of an external DNS recursive resolver.  The B4 will treat the DNS
   packets as normal IP packets and forward them over the softwire.
   Note that there is no effective way to provision an IPv4 DNS address
   to the B4 over IPv6; operators who use this DNS deployment model must
   be aware that how to provision an IPv4 DNS address over an IPv6
   network is undefined, so it will introduce additional complexity in
   B4 provisioning.  Moreover, this will increase the load to the AFTR
   by creating entries in the NAT table for DNS sessions.  Operators may
   deploy a local DNS caching resolver in the AFTR to reduce the load in
   the NAT table.  Nonetheless, this DNS model is not covered in
   [RFC6333] and is not recommended.

3.2.  IPv4 Service Monitoring

3.2.1.  B4 Remote Management

   B4 is connected to the IPv6 access network to offer IPv4 services.
   When users experience IPv4 connectivity issues, operators must be
   able to remotely access (e.g., TR-069) the B4 to verify its
   configuration and status.  Operators should access B4s using native
   IPv6.  Operators should not access B4 over the softwire.

3.2.2.  IPv4 Connectivity Check

   The DS-Lite framework provides IPv4 services over the IPv6 access
   network.  Operators and users must be able to check the IPv4
   connectivity from the B4 to its AFTR using ping and IPv4 traceroute.
   The AFTR should be configured with an IPv4 address to enable a PING
   test and a Traceroute test.  Operators should assign the same IPv4
   address (e.g., 192.0.0.2/32 [RFC6333]) to all AFTRs.  IANA has
   allocated the 192.0.0.0/29 network prefix to provide IPv4 addresses
   for this purpose [RFC6333].



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4.  Security Considerations

   This document does not present any new security issues.  [RFC6333]
   discusses DS-Lite related security issues.

5.  Acknowledgements

   Thanks to Mr. Nejc Skoberne and Dr. Maoke Chen for their thorough
   review and helpful comments.  We also want to thank Mr. Hu Jie for
   sharing his DS-Lite deployment experience with us.  He gave us
   recommendations of what his company learned while testing DS-Lite in
   the production network.

6.  References

6.1.  Normative References

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

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

   [RFC6519]      Maglione, R. and A. Durand, "RADIUS Extensions for
                  Dual-Stack Lite", RFC 6519, February 2012.

6.2.  Informative References

   [DS-LITE]      Boucadair, M., Jacquenet, C., Grimault, J., Kassi-
                  Lahlou, M., Levis, P., Cheng, D., and Y. Lee,
                  "Deploying Dual-Stack Lite in IPv6 Network", Work in
                  Progress, April 2011.

   [NAT-REVEAL]   Boucadair, M., Touch, J., Levis, P., and R. Penno,
                  "Analysis of Solution Candidates to Reveal a Host
                  Identifier (HOST_ID) in Shared Address Deployments",
                  Work in Progress, March 2013.

   [NAT-STANDBY]  Xu, X., Boucadair, M., Lee, Y., and G. Chen,
                  "Redundancy Requirements and Framework for Stateful
                  Network Address Translators (NAT)", Work in Progress,
                  October 2010.

   [PCP-BASE]     Wing, D., Cheshire, S., Boucadair, M., Penno, R., and
                  P. Selkirk, "Port Control Protocol (PCP)", Work in
                  Progress, November 2012.



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   [RFC2473]      Conta, A. and S. Deering, "Generic Packet Tunneling in
                  IPv6 Specification", RFC 2473, December 1998.

   [RFC2475]      Blake, S., Black, D., Carlson, M., Davies, E., Wang,
                  Z., and W. Weiss, "An Architecture for Differentiated
                  Services", RFC 2475, December 1998.

   [RFC2983]      Black, D., "Differentiated Services and Tunnels",
                  RFC 2983, October 2000.

   [RFC3022]      Srisuresh, P. and K. Egevang, "Traditional IP Network
                  Address Translator (Traditional NAT)", RFC 3022,
                  January 2001.

   [RFC4035]      Arends, R., Austein, R., Larson, M., Massey, D., and
                  S. Rose, "Protocol Modifications for the DNS Security
                  Extensions", RFC 4035, March 2005.

   [RFC5245]      Rosenberg, J., "Interactive Connectivity Establishment
                  (ICE): A Protocol for Network Address Translator (NAT)
                  Traversal for Offer/Answer Protocols", RFC 5245,
                  April 2010.

   [RFC5625]      Bellis, R., "DNS Proxy Implementation Guidelines",
                  BCP 152, RFC 5625, August 2009.

   [RFC5985]      Barnes, M., "HTTP-Enabled Location Delivery (HELD)",
                  RFC 5985, September 2010.

   [RFC6269]      Ford, M., Boucadair, M., Durand, A., Levis, P., and P.
                  Roberts, "Issues with IP Address Sharing", RFC 6269,
                  June 2011.

   [RFC6280]      Barnes, R., Lepinski, M., Cooper, A., Morris, J.,
                  Tschofenig, H., and H. Schulzrinne, "An Architecture
                  for Location and Location Privacy in Internet
                  Applications", BCP 160, RFC 6280, July 2011.

   [RFC6302]      Durand, A., Gashinsky, I., Lee, D., and S. Sheppard,
                  "Logging Recommendations for Internet-Facing Servers",
                  BCP 162, RFC 6302, June 2011.










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Authors' Addresses

   Yiu L. Lee
   Comcast
   One Comcast Center
   Philadelphia, PA  19103
   U.S.A.

   EMail: yiu_lee@cable.comcast.com
   URI:   http://www.comcast.com


   Roberta Maglione
   Cisco Systems
   181 Bay Street
   Toronto, ON  M5J 2T3
   Canada

   EMail: robmgl@cisco.com


   Carl Williams
   MCSR Labs
   U.S.A.

   EMail: carlw@mcsr-labs.org


   Christian Jacquenet
   France Telecom
   Rennes
   France

   EMail: christian.jacquenet@orange.com


   Mohamed Boucadair
   France Telecom
   Rennes
   France

   EMail: mohamed.boucadair@orange.com









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