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Network Working Group                                              X. Xu
Internet-Draft                               Huawei Technologies Co.,Ltd
Intended status: Informational                              M. Boucadair
Expires: April 23, 2011                                   France Telecom
                                                                  Y. Lee
                                                                 Comcast
                                                                 G. Chen
                                                            China Mobile
                                                        October 20, 2010


   Redundancy Requirements and Framework for Stateful Network Address
                           Translators (NAT)
                draft-xu-behave-stateful-nat-standby-06

Abstract

   This document defines a set of requirements and a framework for
   ensuring redundancy for stateful Network Address Translators (NAT),
   including NAT44, NAT64 and NAT46.

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 RFC 2119 [RFC2119].

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on April 23, 2011.

Copyright Notice

   Copyright (c) 2010 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
   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.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Terminology and Acronyms . . . . . . . . . . . . . . . . . . .  3
     2.1.  Acronyms . . . . . . . . . . . . . . . . . . . . . . . . .  3
     2.2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  Reference Architecture . . . . . . . . . . . . . . . . . . . .  5
   4.  Dynamic and Static States  . . . . . . . . . . . . . . . . . .  6
   5.  Overview of Redundancy Mechanisms  . . . . . . . . . . . . . .  6
   6.  Cold Standby Mode  . . . . . . . . . . . . . . . . . . . . . .  8
     6.1.  Internal Realm . . . . . . . . . . . . . . . . . . . . . .  8
     6.2.  External Realm . . . . . . . . . . . . . . . . . . . . . .  8
     6.3.  NAT Reachability Announcement  . . . . . . . . . . . . . .  9
   7.  Hot Standby Mode . . . . . . . . . . . . . . . . . . . . . . . 10
     7.1.  Internal Realm . . . . . . . . . . . . . . . . . . . . . . 10
     7.2.  External Realm . . . . . . . . . . . . . . . . . . . . . . 10
     7.3.  NAT Reachability Announcement  . . . . . . . . . . . . . . 10
   8.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 11
   9.  Security Considerations  . . . . . . . . . . . . . . . . . . . 11
   10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 11
   11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11
     11.1. Normative References . . . . . . . . . . . . . . . . . . . 11
     11.2. Informative References . . . . . . . . . . . . . . . . . . 11
   Appendix A.  State Synchronization Protocol Considerations . . . . 12
   Appendix B.  Election Protocol Considerations  . . . . . . . . . . 13
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 14














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1.  Introduction

   Network Address Translation (NAT) has been used as an efficient way
   to share the same IPv4 address among several hosts.  Recently, due to
   IPv4 address shortage, several proposals have been elaborated to rely
   on Carrier Grade NAT (CGN, a.k.a.- LSN for Large Scale NAT) (e.g.,
   [I-D.shirasaki-nat444-isp-shared-addr],
   [I-D.ietf-softwire-dual-stack-lite] and
   [I-D.ietf-behave-v6v4-xlate-stateful]).  In such models, CGN function
   (which may be embedded in a router or be deployed in standalone
   devices) is deployed within large-scale networks, such as ISP
   networks or enterprise ones, where a large number of customers are
   located.  These customers within a network which is served by a
   single CGN device may experience service degradation due to the
   presence of the single point of failure or loss or state information.
   Therefore, redundancy capabilities of the CGN devices are strongly
   desired in order to deliver highly available services to customers.
   Failure detection and repair time must be therefore shortened.

   This document describes a framework of redundancy for stateful NAT
   including: NAT44 including DS-Lite, NAT64 and NAT46.

   The main purpose of this document is to analyze means to ensure high
   availability in environments where carrier grade NAT44, NAT64 and
   NAT46 are deployed.  Some engineering recommendations are provided
   for the selection of the IPv6 prefix to build IPv4-Embedded IPv6
   addresses [I-D.ietf-behave-address-format] and the routing
   configuration.

   Except dealing with the exceptional failures (e.g., power outage, OS
   crash-down or link failure, etc.), the redundancy mechanism described
   in this document can also be used for planned maintenance operations
   (i.e., graceful shutdown of the Primary NAT due to maintenance
   needs).

   Unless otherwise mentioned, NAT and CGN terms throughout this
   document, pertain to stateful NAT and stateful CGN.  Stateless NAT is
   out of the scope of this document.


2.  Terminology and Acronyms

2.1.  Acronyms








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   CGN     Carrier Grade NAT
   LSN     Large Scale NAT
   DS-Lite Dual Stack Lite
   AFTR    Address Family Transition Router
   NAT     Network Address Translation
   ISP     Internet Service Provider

2.2.  Terminology

   This document makes use of the terms defined in [RFC2663].  Below are
   provided terms specific to this document:

   o  CGN (Carrier Grade NAT) or LSN (Large Scale NAT): a NAT device
      placed within a large-scale network (e.g., ISP network, enterprise
      network, or campus network).  CGN may be placed at the boundary
      between the large-scale private network and the public Internet,
      between a private network and a large-scale public network or
      between two heterogeneous IP realms (i.e., IPv4 and IPv6).

   o  CGN internal address realm (internal realm for short): a realm
      internal to the CGN.

         For NAT44, the internal realm refers to the private networks.

         For NAT64, the internal realm means IPv6 network or IPv6
         Internet.

         For NAT46, the internal realm refers to IPv4 network or IPv4
         Internet.

         For DS-Lite, the internal address realm is assumed to be
         private IPv4 addresses even if the transport mode used to
         convey exchanged traffic is IPv6.  A DS-Lite CGN device
         (a.k.a., Address Family Transition Router) is a special NAT44
         function which uses the IPv6 address as a means to de-multiplex
         users sharing the same IPv4 address
         [I-D.ietf-softwire-dual-stack-lite].

   o  The hosts located in the internal realm are called internal hosts,
      and the addresses used in the internal realm are called internal
      addresses.

   o  CGN external address realm (external realm for short): a realm
      external to the CGN.

         For NAT44, the external realm refers to the IPv4 Internet.





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         For NAT64, the external realm means the IPv4 Internet or IPv4
         network.

         For NAT46, the external realm refers to the IPv6 Internet or
         IPv6 network.

   o  The hosts located in the external realm are called external hosts,
      and the addresses used in the external realm are called external
      addresses.

   o  Internal address pool: an address pool used for assigning internal
      addresses to represent the external hosts in the internal realm.
      This address pool is specific to NAT46 and NAT64.

         For NAT46, the CGN will allocate one internal address (which is
         an IPv4 address) from the pool to an external IPv6 host and map
         the external IPv6 host's IPv6 address to this IPv4 address.

         For NAT64, the CGN internal address pool is the Prefix64
         [I-D.ietf-behave-address-format].  Prefix64 is used for
         synthesizing internal IPv6 addresses to represent external IPv4
         hosts in the internal realm.

   o  External address pool: an address pool used by the CGN for
      assigning external addresses to the internal hosts.

         For NAT44 and NAT64, the external address pool contains a set
         of public IPv4 addresses.

         For NAT46, the external IPv6 address pool is the Prefix64.
         Prefix64 is used by the CGN for synthesizing the external IPv6
         addresses to represent internal IPv4 hosts in the external
         realm.

   o  CPE (Customer Premises Equipment): a device which is used to
      interconnect the customer premise with the service provider's
      network.


3.  Reference Architecture

   In a typical operational scenario, as illustrated in Figure 1, two
   NAT devices are deployed for redundancy purposes.  This is the
   reference architecture for the mechanisms we describe in this memo.
   Note that these mechanisms are also suitable in scenarios where more
   than two NAT devices are used.





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           +-------------------------+     +-----------------------+
           |                         |     |                       |
           |                       +-+-----+-+                     |
           |                       |  NAT-A  |                     |
      +----+-------------+         +-+-----+-+    +-------------+  |
      |   Internal Host  |           |     |      |External Host|  |
      +----+-------------+           |     |      +-------------+  |
           |                       +-+-----+-+                     |
           |                       |  NAT-B  |                     |
           |    Internal realm     +-+-----+-+    External realm   |
           |                         |     |                       |
           +-------------------------+     +-----------------------+

              Figure 1: General Scenario of Dual NAT Routers

   The redundancy mechanisms for NAT44, NAT46 and NAT64 are almost
   identical.  In all cases, the NAT device or the immediate router of
   the NAT device announces the reachability of the NAT device to the
   external realm.  The slight difference is the NAT reachability
   information.  For example, NAT64 announces an IPv6 route for the
   Prefix64; NAT44 announces an IPv4 default route; DS-Lite AFTR
   announces an IPv6 route pointing to itself; and NAT46 announces a
   route for its internal address pool.  This difference does not affect
   the general redundancy mechanisms, so the mechanisms described in
   this memo can be applied to NAT44, NAT64 and NAT46 devices.


4.  Dynamic and Static States

   The NAT states mentioned in this document only mean those NAT states
   which are created dynamically by outgoing packets, rather than those
   static NAT states which are configured manually or with automatic
   means such as UPnP or PCP.  For those static NAT states (a.k.a., port
   forwarding entries), they are essentially part of the configuration
   data.

   Port forwarding entries SHOULD be stored in permanent storage
   whatever the deployed redundancy mode.


5.  Overview of Redundancy Mechanisms

   The fundamental principle of NAT redundancy is to make two or more
   NAT devices function as a redundancy group, and select one as the
   Primary NAT and the other(s) as the Backup NAT through a dedicated
   election procedure or manual configuration.

   In the nominal regime, traffic exchanged between one host in the



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   internal realm and another host in the external realm is handled by
   the Primary NAT.  Once the Primary NAT is out of service, the Backup
   NAT with the highest priority (if several Backup NAT devices are
   deployed) takes over and provides the NAT services to the internal
   hosts.  This Backup NAT is then identified as new Primary NAT.  Once
   the former Primary NAT became operational, it could either preempt
   the role of Primary NAT or stay as a candidate in the redundancy
   group.  This is part of administrative policies and out of scope of
   this memo.

   In order to implement the aforementioned procedure, means to detect
   and to notify the failure of the Primary NAT to the redundancy group
   SHOULD be activated.

   To ensure a coherent behavior when NAT device fails, this document
   assumes that both Primary and Backup NAT devices are managed by the
   same administrative domain.  Thus, consistent configuration policies
   SHOULD be enforced in all devices.  Note that the election process
   MUST be deterministic and does not lead to ambiguous situation where
   two or more NAT devices become Primary NAT.  Moreover, the failover
   SHOULD be quick to ensure service continuity and keep end-users from
   perceiving service unavailability.

   Three redundancy modes are described hereafter: the cold standby, the
   hot standby and the partial hot standby modes:

   1.  The cold standby mode is simple.  The NAT states are not
       replicated from the Primary NAT to the Backup NAT.  When the
       Primary NAT fails, all the existing established sessions will be
       flushed out.  The internal hosts are required to re-establish
       sessions to the external hosts;

   2.  The hot standby mode keeps established sessions while failover
       happens.  NAT states are replicated from the Primary NAT to the
       Backup NAT.  When the Primary NAT fails, the Backup NAT will take
       over all the existing established sessions.  The internal hosts
       are not required to re-establish sessions to the external hosts.

   3.  The partial hot standby mode is a flavor of the hot standby mode
       described above.  It is used to avoid replicating NAT states of
       trivial sessions (e.g., short lifetime sessions) while achieving
       hot standby for significant sessions (e.g., critical protocols or
       applications, long lifetime sessions etc.).  Criteria for
       sessions to be replicated on backup NATs SHOULD be explicitly
       configured on the NAT devices of a redundancy group.

   The following sections provide more information about the cold
   standby and the hot standby modes.



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6.  Cold Standby Mode

6.1.  Internal Realm

   The internal addresses used to represent the external hosts in the
   internal realm SHOULD be retained after the NAT failover.  The
   following assesses how this requirement is met in each NAT flavor:

   o  For NAT44 and DS-Lite, the external hosts' internal addresses
      (i.e., the addresses used to represent the external hosts in the
      internal realm) are unchanged (i.e., not NAT-ed).  Therefore, the
      above requirement is met without additional work.

   o  For NAT64, the NAT devices belonging to a redundancy group SHOULD
      be configured with an identical Prefix64.  Since the NAT64 uses
      stateless address translation for the external hosts, using the
      same Prefix64 in the Backup NAT can guarantee the internal hosts
      to see the same internal addresses for the external hosts.

   o  For NAT46, NAT devices in a redundancy group SHOULD be configured
      with an identical IPv4 address pool.  A subset of translation
      state information SHOULD be synchronized among these NAT devices
      through a dedicated state synchronization protocol such as
      [I-D.xu-behave-nat-state-sync].  This translation state ensures
      that the Backup NAT, once taking over as a Primary NAT, will
      assign the same IPv4 addresses to the external IPv6 hosts for the
      internal IPv4 hosts.

6.2.  External Realm

   Each NAT device in a NAT redundancy group is configured with a
   different external address pool.  A route to that external pool is
   then announced into the external realm by the NAT device or the NAT
   immediate router.

   o  For NAT44, DS-Lite and NAT64: NAT devices SHOULD be configured
      with different external IPv4 address pools.  These address pools
      are not overlapped.  Otherwise, when the Primary NAT fails and the
      Backup NAT takes over the Primary NAT, a NAT collision may happen.
      For example, assuming a Primary NAT NAT-ed internal host Host-A to
      IPv4-A.  IPv4-A is an address which belongs to the external
      address pool.  If the Backup NAT after taking over the primary NAT
      was configured with the same pool, the Backup NAT MAY assign the
      same IPv4-A to another internal host Host-B.  So, Host-B may
      receive datagrams originally targeted for Host-A.  This might
      cause confusion to Host-B.  In addition, by using different
      external address pools on each NAT device, incoming datagrams of a
      given session from the external hosts are ensured to always



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      traverse through the Backup NAT device after the Primary NAT
      failover happens.

   o  For NAT46, the issue occurred in NAT44 and NAT64 cases will not
      happen.  NAT46 relies on stateless address translation for the
      internal hosts.  The Primary and Backup NAT SHOULD use the same
      external Prefix64, hence the external hosts can use the Backup
      NAT46 to reach the internal hosts.  In Cold Standby mechanism, the
      Primary and Backup NAT MAY use different Prefix64s.  In contrast,
      the Primary and Backup NAT in Hot Standby mechanism MUST use an
      identical Prefix64.

6.3.  NAT Reachability Announcement

   In order to force the IP datagrams from the internal realm to always
   traverse through the Primary NAT to the external realm, the Primary
   NAT SHOULD announce into the internal realm a route towards the
   external realm.

   o  For NAT44, the Primary NAT announces an IPv4 default route into
      the internal realm.

   o  For DS-Lite, the Primary NAT announces a host route into the
      internal realm.

   o  For NAT64, the Primary NAT announces a route for the Prefix64 into
      the internal realm.

   o  For NAT46, the Primary NAT announces a route for the internal
      address pool into the internal realm (If the internal address pool
      can be aggregated to one prefix).

   The Primary NAT SHOULD attempt to withdraw its previously announced
   routes when it ceases the Primary role due to pre-configured
   conditions, e.g.- it loses the IP connectivity to the external realm.

   When the Primary NAT fails and the Backup NAT takes over, datagrams
   from the internal hosts destined for the external realm SHOULD pass
   through the Backup NAT.  Hence, when the Backup NAT is manually
   configured to switch over to become the Primary NAT, the Backup NAT
   (or associated router) SHOULD announce the same route into the
   internal realm, but the routing cost of this route MUST be set to a
   higher value than the route announced by the Primary NAT.

   Alternatively, the Primary NAT announces several more specific routes
   into the internal realm while the Backup NAT announces an aggregate
   route.  Taken the NAT46 as an example, assuming the internal address
   pool is 10.0.0.0/8, the Primary NAT announces two more specific



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   routes to 10.0.0.0/9 and 10.128.0.0/9 respectively while the Backup
   NAT announces an aggregate route to 10.0.0.0/8.  In case the Primary
   NAT and the Backup NAT are automatically elected through a dedicated
   election process, the Backup NAT would be elected as a new Primary
   NAT once the old Primary one fails, so it is not necessary for the
   Backup NAT to make the above route announcements until it is elected
   as a new Primary NAT.

   In order for the external hosts to traverse through the NAT to reach
   the internal hosts, the Primary and Backup NAT SHOULD announce a
   route of its own external address pool into the external realm.


7.  Hot Standby Mode

7.1.  Internal Realm

   The procedure is identical to Section 6.1.

7.2.  External Realm

   To preserve the established sessions during the failover and to keep
   the internal addresses unchanged for the external hosts, the external
   addresses for the internal hosts MUST also be preserved.  To preserve
   the external address of the internal host after NAT-ed, the NAT
   devices in a redundancy group MUST use an identical external address
   pool.  In addition, they MUST assign the same external address (or
   address/port pair) to a given internal host.

   o  For NAT46, the Primary NAT and Backup NAT MUST use an identical
      Prefix64.

   o  For NAT44, DS-Lite and NAT64, the NAT devices in a redundancy
      group MUST use the same external address pool and the translation
      states on the Primary NAT device MUST be synchronized to the
      Backup NAT(s) in a timely fashion.

7.3.  NAT Reachability Announcement

   In order to force IP datagrams between the internal realm and the
   external realm always traverse through the Primary NAT, the Primary
   NAT (or its associated router) SHOULD announce into the internal
   realm a route towards the external realm and announce into the
   external realm a route towards the external address pool.

   Once the connectivity to either the external realm or the internal
   realm is lost, the Primary NAT device itself or a third party SHOULD
   attempt to withdraw the above routes.  If the Primary NAT and the



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   Backup NAT are specified manually, the Backup NAT device (or its
   associated router) SHOULD also announce those routes, but with higher
   enough cost or larger granularity, so as to prepare for the failover.

   When the Primary NAT fails, the datagrams towards the external realm
   will pass through the Backup NAT device.  In case the Primary NAT and
   the Backup are automatically elected through a dedicated election
   procedure, the Backup NAT would be elected as a new Primary NAT when
   the old Primary NAT device fails.  Consequently, it is not necessary
   for the Backup NAT to make the above route announcement until it is
   elected as a new Primary NAT.


8.  IANA Considerations

   This document makes no request of IANA.

   Note to RFC Editor: this section may be removed on publication as an
   RFC.


9.  Security Considerations

   TBD.


10.  Acknowledgements

   The author would like to thank Dan Wing and Dave Thaler for their
   insightful comments and reviews, and thank Dacheng Zhang and Xuewei
   Wang for their valuable editorial reviews.


11.  References

11.1.  Normative References

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

11.2.  Informative References

   [I-D.ietf-behave-address-format]
              Bao, C., Huitema, C., Bagnulo, M., Boucadair, M., and X.
              Li, "IPv6 Addressing of IPv4/IPv6 Translators",
              draft-ietf-behave-address-format-10 (work in progress),
              August 2010.




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   [I-D.ietf-behave-v6v4-xlate-stateful]
              Bagnulo, M., Matthews, P., and I. Beijnum, "Stateful
              NAT64: Network Address and Protocol Translation from IPv6
              Clients to IPv4 Servers",
              draft-ietf-behave-v6v4-xlate-stateful-12 (work in
              progress), July 2010.

   [I-D.ietf-softwire-dual-stack-lite]
              Durand, A., Droms, R., Woodyatt, J., and Y. Lee, "Dual-
              Stack Lite Broadband Deployments Following IPv4
              Exhaustion", draft-ietf-softwire-dual-stack-lite-06 (work
              in progress), August 2010.

   [I-D.shirasaki-nat444-isp-shared-addr]
              Shirasaki, Y., Miyakawa, S., Nakagawa, A., Yamaguchi, J.,
              and H. Ashida, "NAT444 addressing models",
              draft-shirasaki-nat444-isp-shared-addr-04 (work in
              progress), July 2010.

   [I-D.xu-behave-nat-state-sync]
              Cheng, D. and X. Xu, "NAT State Synchronization Using
              SCSP", draft-xu-behave-nat-state-sync-02 (work in
              progress), August 2010.

   [RFC2334]  Luciani, J., Armitage, G., Halpern, J., and N. Doraswamy,
              "Server Cache Synchronization Protocol (SCSP)", RFC 2334,
              April 1998.

   [RFC2663]  Srisuresh, P. and M. Holdrege, "IP Network Address
              Translator (NAT) Terminology and Considerations",
              RFC 2663, August 1999.

   [RFC4761]  Kompella, K. and Y. Rekhter, "Virtual Private LAN Service
              (VPLS) Using BGP for Auto-Discovery and Signaling",
              RFC 4761, January 2007.

   [RFC4762]  Lasserre, M. and V. Kompella, "Virtual Private LAN Service
              (VPLS) Using Label Distribution Protocol (LDP) Signaling",
              RFC 4762, January 2007.

   [RFC5798]  Nadas, S., "Virtual Router Redundancy Protocol (VRRP)
              Version 3 for IPv4 and IPv6", RFC 5798, March 2010.


Appendix A.  State Synchronization Protocol Considerations

   [I-D.xu-behave-nat-state-sync] defines a candidate solution to NAT
   state synchronization by using Server Cache Synchronization Protocol



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   (SCSP) [RFC2334].  For more information about the proposed solution,
   refer to [I-D.xu-behave-nat-state-sync].

   [[Note: What to do with this section?]]


Appendix B.  Election Protocol Considerations

   [[Note: What to do with this section?]]

   An election process and associated protocol(s) can be used to
   automatically elect one NAT device among a NAT redundancy group as
   the Primary NAT and the others as Backup NATs.  Once the Primary NAT
   fails, the Backup NAT with the highest priority SHOULD take over the
   Primary NAT role after a short delay.  The election protocol is also
   used to track the connectivity to the external realm and the internal
   realm.  Once connections to the external realm or the internal realm
   lost, the NAT device is not qualified to be the Primary NAT and it
   will withdraw the route towards the external realm announced
   previously.  In the case of hot standby, it SHOULD also withdraw the
   route towards the external address pool.

   As an implementation example, VRRP [RFC5798] can be used as the
   automatic election protocol.  In addition, an interface tracking
   mechanism can also be used to adjust the priority to influence the
   election results.

   If two NAT devices are directly connected via an Ethernet network,
   VRRP can run directly on the Ethernet interfaces.  Otherwise, some
   extra configuration or protocol changes need to be implemented.  One
   option is to create conditions for VRRP to run among these devices.
   For example, to create a VPLS [RFC4761][RFC4762] instance and enable
   IP functions and run VRRP on those VLAN interfaces which are bound to
   that VPLS instance.  If enabling IP on those interfaces is not
   supported, the following trick to realize the same goal, but at a
   cost of consuming two physical interfaces on each NAT router: create
   a VPLS instance among a set of NAT devices, and on each of them one
   Ethernet interface is bound to that VPLS instance, and another IP-
   enabled Ethernet interface is locally connected with that interface.
   Then VRRP can run on those IP enabled Ethernet interfaces which are
   all connected to that VPLS instance.  Another option is to extend
   VRRP so that VRRP neighbors can be specified manually and VRRP
   messages can be exchanged directly among VRRP neighbors in unicast.

   VRRP is only an implementation example of the election process.
   Other protocols MAY be used to manage the roles of Primary and
   Backup.




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Internet-Draft       Redundancy for NAT Requirements        October 2010


Authors' Addresses

   Xiaohu Xu
   Huawei Technologies Co.,Ltd
   KuiKe Building, No.9 Xinxi Rd.,
   Hai-Dian District, Beijing  100085
   P.R. China

   Email: xuxh@huawei.com


   Mohamed Boucadair
   France Telecom
   Rennes
   France

   Email: mohamed.boucadair@orange-ftgroup.com


   Yiu L. Lee
   Comcast

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


   Gang Chen
   China Mobile
   53A,Xibianmennei Ave.
   Beijing,   100053
   P.R.China

   Email: phdgang@gmail.com


















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