CGN Deployment with BGP/MPLS IP VPNs
draft-ietf-opsawg-lsn-deployment-01

OPSAWG                                                 V. Kuarsingh, Ed.
Internet-Draft                                             J. Cianfarani
Intended status: Informational                     Rogers Communications
Expires: April 18, 2013                                 October 15, 2012

                  CGN Deployment with BGP/MPLS IP VPNs
                  draft-ietf-opsawg-lsn-deployment-01

Abstract

   This document specifies a framework to integrate a Network Address
   Translation layer into an operator's network to function as a Carrier
   Grade NAT (also known as CGN or Large Scale NAT).  The CGN
   infrastructure will often form a NAT444 environment as the subscriber
   home network will likely also contain a NAT function.  Exhaustion of
   the IPv4 address pool is a major driver compelling some operators to
   implement CGN.  Although operators may wish to deploy IPv6 to
   strategically overcome IPv4 exhaustion, near term needs may not be
   satisfied with an IPv6 deployment alone.  This document provides a
   practical integration model which allows the CGN platform to be
   integrated into the network meeting the connectivity needs of the
   subscriber while being mindful of not disrupting existing services
   and meeting the technical challenges that CGN brings.  The model
   included in this document utilizes BGP/MPLS IP VPNs which allow for
   virtual routing separation helping ease the CGNs impact on the
   network.  This document does not intend to defend the merits of CGN.

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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   This Internet-Draft will expire on April 18, 2013.

Copyright Notice

   Copyright (c) 2012 IETF Trust and the persons identified as the

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   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Motivation . . . . . . . . . . . . . . . . . . . . . . . . . .  3
   3.  CGN Network Deployment Requirements  . . . . . . . . . . . . .  4
     3.1.  Centralized versus Distributed Deployment  . . . . . . . .  5
     3.2.  CGN and Traditional IPv4 Service Co-existence  . . . . . .  6
     3.3.  CGN By-Pass  . . . . . . . . . . . . . . . . . . . . . . .  6
     3.4.  Routing Plane Separation . . . . . . . . . . . . . . . . .  6
     3.5.  Flexible Deployment Options  . . . . . . . . . . . . . . .  7
     3.6.  IPv4 Overlap Space . . . . . . . . . . . . . . . . . . . .  7
     3.7.  Transactional Logging for LSN Systems  . . . . . . . . . .  7
     3.8.  Additional CGN Requirements  . . . . . . . . . . . . . . .  8
   4.  BGP/MPLS IP VPN based CGN Framework  . . . . . . . . . . . . .  8
     4.1.  Service Separation . . . . . . . . . . . . . . . . . . . .  9
     4.2.  Internal Service Delivery  . . . . . . . . . . . . . . . . 10
       4.2.1.  Dual Stack Operation . . . . . . . . . . . . . . . . . 11
     4.3.  Deployment Flexibility . . . . . . . . . . . . . . . . . . 13
     4.4.  Comparison of BGP/MPLS IP VPN Option versus other CGN
           Attachment Options . . . . . . . . . . . . . . . . . . . . 13
       4.4.1.  Policy Based Routing . . . . . . . . . . . . . . . . . 13
       4.4.2.  Traffic Engineering  . . . . . . . . . . . . . . . . . 14
       4.4.3.  Multiple Routing Topologies  . . . . . . . . . . . . . 14
   5.  Experiences  . . . . . . . . . . . . . . . . . . . . . . . . . 14
     5.1.  Basic Integration and Requirements Support . . . . . . . . 14
     5.2.  Performance  . . . . . . . . . . . . . . . . . . . . . . . 15
   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 15
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 15
   8.  Conclusions  . . . . . . . . . . . . . . . . . . . . . . . . . 15
   9.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 16
   10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 16
     10.1. Normative References . . . . . . . . . . . . . . . . . . . 16
     10.2. Informative References . . . . . . . . . . . . . . . . . . 16
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 17

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1.  Introduction

   Operators are faced with near term IPv4 address exhaustion
   challenges.  Many operators may not have a sufficient amount of IPv4
   addresses in the future to satisfy the needs of their growing
   subscriber base.  This challenge may also be present before or during
   an active transition to IPv6 somewhat complicating the overall
   problem space.

   To face this challenge, operators may need to deploy CGN (Carrier
   Grade NAT) as described in [I-D.ietf-behave-lsn-requirements] to help
   extend the connectivity matrix once IPv4 addresses run out in the
   network.  CGN deployments will most often be added into operator
   networks which already have active IPv4 and/or IPv6 services.

   The addition of the CGN introduces an operator controlled and
   administered translation layer which should be added in a manner
   which minimizes disruption to existing services.  This addition may
   also include interworking in a dual stack environment where the IPv4
   path requires translation.

   This document shows how BGP/MPLS IP VPNs as described in [RFC4364]
   can be used to integrate the CGN infrastructure solving key
   integration challenges faced by the operator.  This model has also
   been tested and validated in real production network models and
   allows fluid operation with existing IPv4 and IPv6 services.

2.  Motivation

   The selection of CGN may be made by an operator based on a number of
   factors.  The overall driver may be the depletion of IPv4 address
   pools which leaves little to no addresses for IPv4 service growth.
   IPv6 is considered the strategic answer, but it's applicability and
   usefulness in many networks is limited by the current access network
   and consumer home network.  These environments often are filled with
   IPv4-Only equipment which may not be upgradable to IPv6.

   The ability to replace IPv4-Only equipment may be out of the control
   of the operator, and even when it's in the administrative control; it
   poses both cost and technical challenges as operators build out
   massive programs for equipment retirement or upgrade.  Theses issues
   leave an operator in a precarious position which may lead to the
   decision to deploy CGN.  Other address IPv4 sharing options do exist
   which are more architecturally desirable, but the practical and
   workable approach in many cases is a CGN deployment using NAT444.

   If the operator as has chosen to deploy CGN, they should this in a

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   manner as not to negatively impact the existing IPv4 or IPv6
   subscriber base.  This will include solving a number of challenges
   since subscribers who's connections require translation will have
   network routing and flow needs which are different from legacy IPv4
   connections.

   The solution will also need to work in a dual stack environment where
   other options such as DS-Lite [RFC6333] are not yet viable.  Even
   technologies like 6RD [RFC5969] still require an IPv4 connectivity
   path to service the subscriber endpoint.  The solution will need to
   address basic Internet connectivity, on-net service offerings, back
   office management, billing, policy and security models already in
   place within the operator's network.  CGN will often integrate quite
   readily with the aforementioned requirements where as other
   transition mechanism may not due to the requirements to support IPv6
   as the base protocol for IPv4 connectivity.

3.  CGN Network Deployment Requirements

   If a service provider is considering a CGN deployment with a provider
   NAT44 function, there are a number of basic requirements which are of
   importance.  Preliminary requirements may require the following from
   the incoming CGN system architecture:

      - Support distributed (sparse) and centralized (dense) deployment
      models;

      - Allow co-existence with traditional IPv4 based deployments,
      which provide global scoped IPs to CPEs;

      - Provide a framework for CGN by-pass supporting non-translated
      flows between endpoints within a provider's network;

      - Provide routing framework which allows the segmentation of
      routing control and forwarding paths between CGN and non-CGN
      mediated flows;

      - Provide flexibility for operators to modify their deployments
      over time as translation demands change (connections, bandwidth,
      translation realms/zones and other vectors);

      - Flexibility should include integration options for common access
      technologies such as DSL (BRAS), DOCSIS (CMTS), Mobile (GGSN/PGW/
      ASN-GW), and Ethernet access;

      - Support deployment modes that allow for IPv4 address overlap
      within the operator's network (between various translation realms

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      or zones);

      - Allow for evolution to future dual-stack and IPv4/IPv6
      transition deployment modes;

      - Transactional logging and export capabilities to support
      auxiliary functions including abuse mitigation;

      - Support for stateful connection synchronization between
      translation instances/elements (redundancy);

      - Support for CGN Shared Space [RFC6598] deployment modes if
      applicable;

      - Allows for the enablement of CGN functionality (if required)
      while still minimizing costs and subscriber impact to the best
      extend possible;

   Other requirements may be assessed on a operator-by-operator basis,
   but those listed above should be considered for any given deployment
   architecture.

3.1.  Centralized versus Distributed Deployment

   Centralized deployments of CGN (longer proximity to end user and/or
   higher densities of subscribers/connections to CGN instances) differ
   from distributed deployments of CGN (closer proximity to end user
   and/or lower densities of subscribers/connections to CGN instances).
   Service providers will likely deploy CGN translation points more
   centrally during initial phases.  Early deployments will likely see
   light loading on these new systems since legacy IPv4 services will
   continue to operate with most endpoints using globally unique IPv4
   addresses.  Exceptional cases which may drive heavy usage in initial
   stages may include operators who already translate most IPv4 traffic
   and will migrate to a CGN implementation from legacy firewalls; or a
   green field deployment which may see quick growth in the number of
   new IPv4 endpoints which require Internet connectivity.

   Over time, most providers will likely need to expand and possibly
   distribute the translation points as demand for the CGN system
   increases.  The extent of the expansion of the CGN infrastructure
   will depend on factors such as growth in the number of IPv4
   endpoints, status of IPv6 content on the Internet and the overall
   progress globally to an IPv6-dominate Internet (reducing the demand
   for IPv4 connectivity).

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3.2.  CGN and Traditional IPv4 Service Co-existence

   Newer CGN serviced endpoints will exist alongside endpoints served by
   traditional IPv4 global IPs.  Providers will need to rationalize
   these environments since both have distinct forwarding needs.
   Traditional IPv4 services will likely require (or be best served)
   direct forwarding towards Internet peering points while CGN mediated
   flows require access to a translator.  CGN and non-CGN mediated flows
   post two fundamentally different forwarding needs.

   The new CGN environments should not negatively impact the existing
   IPv4 service base by forcing all traffic to translation enabled
   network points since many flows do not require translation and this
   would reduce performance of the existing flows.  This would also
   require massive scaling of the CGN which is a cost and efficiency
   concern as well.

   Traffic flow and forwarding efficiency is considered important since
   networks are under considerable demand to deliver more and more
   bandwidth without the luxury of needless inefficiencies which can be
   introduced with CGN.

3.3.  CGN By-Pass

   The CGN environment is only needed for flows with translation
   requirements.  Many flows which remain in a service provider
   environment, do not require translation.  Such services include
   operator offered DNS Services, DHCP Services, NTP Services, Web
   Caching, Mail, News and other services which are local to the
   operator's network.

   The operator may want to leverage opportunities to offer third
   parties a platform to also provide services without translation.  CGN
   By-pass can be accomplished in many ways, but a simplistic,
   deterministic and scalable model is preferred.

3.4.  Routing Plane Separation

   Many operators will want to engineer traffic separately for CGN flows
   versus flows which are part of the more traditional IPv4 environment.
   Many times the routing of these two major flow types differ,
   therefore route separation may be required.

   Routing plane separation also allows the operator to utilize other
   addressing techniques, which may not be feasible on a single routing
   plane.  Such examples include the use of overlapping private address
   space [RFC1918] or use of other IPv4 space which may overlap globally
   within the operator's network.

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3.5.  Flexible Deployment Options

   Service providers operate complex routing environments and offer a
   variety of IPv4 based services.  Many operator environments utilize
   distributed peering infrastructures for transit and peering and these
   may span large geographical areas and regions.  A CGN solution should
   offer the operator an ability to place CGN translation points at
   various points within their network.

   The CGN deployment should also be flexible enough to change over time
   as demand for translation services increase.  In turn, the deployment
   will need to then adapt as translation demand decreases caused by the
   transition of flows to IPv6.  Translation points should be able to be
   placed and moved with as little re-engineering effort as possible
   minimizing the risks to the subscriber base.

   Depending on hardware capabilities, security practices and IPv4
   address availability, the translation environments my need to be
   segmented and/or scaled over time to meet organic IPv4 demand growth.
   Operators will want to seek deployment models which are conducive to
   meeting these goals as well.

3.6.  IPv4 Overlap Space

   IP address overlap for CGN translation realms may be required if
   insufficient IPv4 addresses are available within the service provider
   environment to assign internally unique IPs to the CGN subscriber
   base .  The CGN deployment should provide mechanisms to manage IPv4
   overlap if required.

3.7.  Transactional Logging for LSN Systems

   CGNs may require transactional logging since the source IP and
   related transport protocol information is not easily visible to
   external hosts and system.

   If needed, the CGN systems should be able to generate logs which
   identify 'internal' host parameters (i.e.  IP/Port) and associated
   them to external translated parameters imposed by the translator.
   The logged information should be stored on the CGN hardware and/or
   exported to an external system for processing.  Operators may need to
   keep track of this information (securely) to meet regulatory and/or
   legal obligations.  Further information can be found in [I-D.ietf-
   behave-lsn-requirements] with respect to CGN logging requirements
   (Logging Section).

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3.8.  Additional CGN Requirements

   The CGN platform will also need to meet the needs of additional
   requirements such as Bulk Port Allocation and other CGN device
   specific functions.  These additional requirements are captured
   within [I-D.ietf-behave-lsn-requirements].

4.  BGP/MPLS IP VPN based CGN Framework

   The BGP/MPLS IP VPN [RFC4364] framework for CGN segregates the 'pre-
   translated' realms within the service provider space into Layer-3
   MPLS based VPNs.  The operator can deploy a single realm for all CGN
   based flows, or can deploy multiple realms based on translation
   demand and other factors such as geographical proximity.  A realm in
   this model refers to a 'VPN' which shares a unique RD/RT combination,
   routing plane and forwarding behaviours.

   The BGP/MPLS IP VPN infrastructure provides control plane and
   forwarding separation for the traditional IPv4 service environment
   and CGN environment(s).  The separation allows for routing
   information (such as default routes) to be propagated separately for
   CGN and non-CGN based subscriber flows.  Traffic can be efficiently
   routed to the Internet for normal flows, and routed directly to
   translators for CGN mediated flows.  Although many operators may run
   a "default-route-free" core, IPv4 flows which require translation
   must obviously be routed first to a translator, so a default route is
   acceptable for the pre-translated realms.

   The physical location of the VRF Termination point for a BGP/MPLS IP
   VPN enabled CGN can vary and be located anywhere within the
   operator's network.  This model fully virtualizes the translation
   service from the base IPv4 forwarding environment which will likely
   carrying Internet bound traffic.  The base IPv4 environment can
   continue to service traditional IPv4 subscriber flows plus post
   translated CGN flows.

   Figure 1 provides a view of the basic model.  The Access node
   provides CPE access to either the CGN VRF or the Global Routing
   Table, depending on whether the subscriber receives a private or
   public IP.  Translator mediated traffic follows an MPLS LSP which can
   be setup dynamically and can span one hop, or many hops (with no need
   for complex routing policies).  Traffic is then forwarded to the
   translator (shown below) which can be an external appliance or
   integrated into the VRF Termination (Provider Edge) router.  Once
   traffic is translated, it is forwarded to the global routing table
   for general Internet forwarding.  The Global Routing table can also
   be a separate VRF (Internet Access VPN/VRF) should the provider

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   choose to implement their Internet based services in that fashion.
   The translation services are effectively overlaid onto the network,
   but are maintained within a separate forwarding and control plane.

                   Access Node     VRF Termination        LSN
                  +-----------+     +-----------+    +-----------+
                  |           |     |           |    |           |
          CPE     | +-------+ |     | +-------+ |    | +-------+ |
         +----+   | |       | | LSP | |       | | IP | |       | |
         |  --+---+-+->VRF--+-+-----+-+->VRF--+-+----+-+->     | |
         +----+   | |       | |     | |       | |    | |       | |
                  | +-------+ |     | +-------+ |    | |       | |
                  |           |     |           |    | | XLATE | |
                  |           |     |           |    | |       | |
          CPE     | +-------+ |     | +-------+ |    | |       | |
         +----+   | |       | |     | |       | | IP | |       | |
         |  --+---+-+->GRT  | |     | |  GRT<-+-+----+-+--     | |
         +----+   | |   |   | |     | |   |   | |    | |       | |
                  | +---+---+ |     | +---+---+ |    | +-------+ |
                  +-----+-----+     +-----+-----+    +-----------+
                        |                 |
                        |                 |                IPv4
                        |                 |   IP       +---------+
                        |                 +------------+->       |
                        |                     IP       |    GRT  |
                        +------------------------------+->       |
                                                       +---------+

                 Figure 1: Basic BGP/MPLS IP VPN CGN Model

   If more then one VRF (translation realm) is used within the
   operator's network, each VPN instance can manage CGN flows
   independently for the respective realm.  Various redundancy models
   can be used within this architecture to support failover from one
   physical CGN hardware instance to another.  If state information
   needs to be passed or maintained between hardware instances, the
   vendor would need to enable this feature in a suitable manner.

4.1.  Service Separation

   The MPLS/VPN CGN framework supports route separation.  The
   traditional IPv4 flows can be separated at the access node (Initial
   Layer 3 service point) from those which require translation.  This
   type of service separation is possible on common technologies used
   for Internet access within many operator networks.  Service
   separation can be accomplished on common access technology including

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   those used for DOCSIS (CMTS), Ethernet Access, DSL (BRAS), and Mobile
   Access (GGSN/ASN-GW) architectures.

4.2.  Internal Service Delivery

   Internal services can be delivered directly to the privately
   addressed endpoint within the CGN domain without translation.  This
   can be accomplished using direct route exchange (import/export)
   between the CGN VRFs and the Services VRFs.  The previous statement
   assumes the provider puts key services into a VRF for simple route
   exchange.  This model allows the provider to maintain separate
   forwarding rules for translated flows, which require a pass through
   the translator to reach external network entities, versus those flows
   which need to access internal services.  This operational detail can
   be advantageous for a number of reasons.

   First, the provider can reduce the load on the translator since
   internal services do not need to be factored into the scaling of the
   CGN hardware.  Secondly, more direct forwarding paths can be
   maintained providing better network efficiency.  Thirdly, geographic
   locations of the translators and the services infrastructure can be
   deployed in a location in an independent manner.  Additionally, the
   operator can allow CGN subject endpoints to be accessible via an
   untranslated path reducing the complexities of provider initiated
   management flows.  This last point is of key interest since NAT
   removes transparency to the end device in normal cases.

   Figure 2 below shows how internal services are provided untranslated
   since flows are sent directly from the access node to the services
   node/VRF via an MPLS LSP.  This traffic is not forwarded to the CGN
   translator and therefore is not subject to problematic behaviours
   related to NAT.  The services VRF contains routing information which
   can be "imported" into the access node VRF and the CGN VRF routing
   information can be "imported" into the Services VRF.

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                     Access Node     VRF Termination     LSN
                   +-------------+    +-----------+  +----------+
                   |             |    |           |  |          |
            CPE    | +---------+ |    | +-------+ |  | +------+ |
          +-----+  | |         | |    | |       | |  | |      | |
          |   --+--+-+-> VRF --+-+--+ | |  VRF  | |  | |      | |
          +-----+  | |         | |  | | |       | |  | |      | |
                   | +---------+ |  | | +-------+ |  | |      | |
                   |             |  | |           |  | |XLATE | |
                   |             |  | |           |  | |      | |
            CPE    | +---------+ |  | | +-------+ |  | |      | |
          +-----+  | |         | |  | | |       | |  | |      | |
          |   --+--+-+-> GRT   | |  | | |  GRT  | |  | |      | |
          +-----+  | |    |    | |  | | |       | |  | |      | |
                   | +----+----+ |  | | +-------+ |  | +------+ |
                   +------+------+  | +-----------+  +----------+
                          |         |
                          |         |                    IPv4
                          |         |               +-----------+
                          |         +---------------+->Services |
                          |                         |    VRF    |
                          .-------------------------+->   |     |
                                                    +-----+-----+
                                                          |
                                                    +-----V-----+
                                                    |           |
                                                    |   Local   |
                                                    |  Content  |
                                                    +-----------+

                Figure 2: Internal Services and CGN By-Pass

   This demonstrates the ability to offer CGN By-Pass in a simple and
   deterministic manner without the need of policy based routing or
   traffic engineering.

4.2.1.  Dual Stack Operation

   The BGP/MPLS IP VPN CGN model can also be used in conjunction with
   IPv4/IPv6 dual stack service modes.  Since many providers will use
   CGNs on an interim basis while IPv6 matures within the global
   Internet or due to technical constraints, a dual stack option is of
   strategic importance.  Operators can offer this dual stack service
   for both traditional IPv4 (global IP) endpoints and CGN mediated
   endpoints.

   Operators can separate the IP flows for IPv4 and IPv6 traffic, or use

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   other routing techniques to move IPv6 based flows towards the GRT
   (Global Routing Table or Instance) while allowing IPv4 flows to
   remain within the IPv4 CGN VRF for translator services.

   The Figure 3 below shows how IPv4 translation services can be
   provided alongside IPv6 based services.  The model shown allows the
   provider to enable CGN to manage IPv4 flows (translated) and IPv6
   flows are routed without translation efficiently towards the
   Internet.  Once again, forwarding of flows to the translator does not
   impact IPv6 flows which do not require this service.

                    Access Node   VRF Termination        LSN
                   +-----------+   +-----------+    +-----------+
                   |           |   |           |    |           |
           CPE     | +-------+ |   | +-------+ |    | +-------+ |
          +-----+  | |       | |LSP| |       | | IP | |       | |
          |   --+--+-+->VRF--+-+---+-+->VRF--+-+----+-+>      | |
          |IPv4 |  | |       | |   | |       | |    | |       | |
          |     |  | +-------+ |   | +-------+ |    | |       | |
          +-----|  |           |   |           |    | | XLATE | |
          |IPv6 |  |           |   |           |    | |       | |
          |     |  | +-------+ |   | +-------+ |    | |       | |
          |     |  | |  IPv6 | |   | |  IPv4 | | IP | |       | |
          |   --+--+-+->GRT  | |   | |  GRT<-+-+----+-+--     | |
          +-----+  | |   |   | |   | |   |   | |    | |       | |
                   | +---+---+ |   | +---+---+ |    | +-------+ |
                   +-----+-----+   +-----+-----+    +-----------+
                         |               |
                         |               |          +-----------+
                         |               |    IP    |    IPv4   |
                         |               +----------+->  GRT    |
                         |                          +-----------+
                         |
                         |
                         |
                         |               IP         +-----------+
                         +--------------------------+->  IPv6   |
                                                    |    GRT    |
                                                    +-----------+

               Figure 3: CGN with IPv6 Dual Stack Operation

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4.3.  Deployment Flexibility

   The CGN translator services can be moved, separated or segmented (new
   translation realms) without the need to change the overall
   translation design.  Since dynamic LSPs are used to forward traffic
   from the access nodes to the translation points, the physical
   location of the VRF termination points can vary and be changed
   easily.

   This type of flexibility allows the service provider to initially
   deploy more centralized translation services based on relatively low
   loading factors, and distribute the translation points over time to
   improve network traffic efficiencies and support higher translation
   load.

   Although traffic engineered paths are not required within the MPLS/
   VPN deployment model, nothing precludes an operator from using
   technologies like MPLS with Traffic Engineering [RFC3031].
   Additional routing mechanisms can be used as desired by the provider
   and can be seen as independent.  There is no specific need to
   diversify the existing infrastructure in most cases.

4.4.  Comparison of BGP/MPLS IP VPN Option versus other CGN Attachment
      Options

   Other integration architecture options exist which can attach CGN
   based service flows to a translator instance.  Alternate options
   which can be used to attach such services include:

      - Policy Based Routing (Static) to direct translation bound
      traffic to a network based translator;

      - Traffic Engineering or;

      - Multiple Routing Topologies

4.4.1.  Policy Based Routing

   Policy Based Routing (PBR) provides another option to direct CGN
   mediated flows to a translator.  PBR options, although possible, are
   difficult to maintain (static policy) and must be configured
   throughout the network with considerable maintenance overhead.

   More centralized deployments may be difficult or too onerous to
   deploy using Policy Based Routing methods.  Policy Based Routing
   would not achieve route separation (unless used with others options),
   and may add complexities to the providers' routing environment.

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4.4.2.  Traffic Engineering

   Traffic Engineering can also be used to direct traffic from an access
   node towards a translator.  Traffic Engineering, like MPLS-TE, may be
   difficult to setup and maintain.  Traffic Engineering provides
   additional benefits if used with MPLS by adding potentials for faster
   path re-convergence.  Traffic Engineering paths would need to be
   updated and redefined overtime as CGN translation points are
   augmented or moved.

4.4.3.  Multiple Routing Topologies

   Multiple routing topologies can be used to direct CGN based flows to
   translators.  This option would achieve the same basic goal as the
   MPLS/VPN option but with additional implementation overhead and
   platform configuration complexity.  Since operator based translation
   is expected to have an unknown lifecycle, and may see various degrees
   of demand (dependant on operator IPv4 Global space availability and
   shift of traffic to IPv6), it may be too large of an undertaking for
   the provider to enabled this as their primary option for CGN.

5.  Experiences

5.1.  Basic Integration and Requirements Support

   The MPLS/VPN CGN environment has been successfully integrated into
   real network environments utilizing existing network service delivery
   mechanisms.  It solves many issues related to provider based
   translation environments, while still subject to problematic
   behaviours inherent within NAT.

   Key issues which are solved or managed with the MPLS/VPN option
   include:

      - Centralized and Distributed Deployment model support

      - Routing Plane Separation for CGN flows versus traditional IPv4
      flows

      - Flexible Translation Point Design (can relocate translators and
      split translation zones easily)

      - Low maintenance overhead (dynamic routing environment with
      little maintenance of separate routing infrastructure other then
      management of MPLS/VPNs)

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      - CGN By-pass options (for internal and third party services which
      exist within the provider domain)

      - IPv4 Translation Realm overlap support (can reuse IP addresses
      between zones with some impact to extranet service model)

      - Simple failover techniques can be implemented with redundant
      translators, such as using a second default route

5.2.  Performance

   The MPLS/VPN CGN model was observed to support basic functions which
   are typically used by subscribes within an operator environment.  A
   full review of the observed impacts related to CGN (NAT444) are
   covered in [I-D.donley-nat444-impacts].

6.  IANA Considerations

   There are not specific IANA considerations known at this time with
   the architecture described herein.  Should a provide choose to use
   non-assigned IP address space within their translation realms, then
   considerations may apply.

7.  Security Considerations

   The same security considerations would typically exist for CGN
   deployments when compared with traditional IPv4 based services.  With
   the MPLS/VPN model, the operator would want to consider security
   issues related to offering IP services over MPLS.

   If a provider plans to operate the pre-translation realm (CPE towards
   translator IPv4 zone) as a non-public like network, then additional
   security measures may be needed to secure this environment.  It is
   however the position in this document that CGN realms are public
   domains which utilize non-Internet routable IP addresses for endpoint
   addressing.

8.  Conclusions

   The MPLS/VPN delivery method for a CGN deployment is an effective and
   scalable way to deliver mass translation services.  The architecture
   avoids the complex requirements of traffic engineering and policy
   based routing when combining these new service flows to existing IPv4
   operation.  This is advantageous since the NAT44/CGN environments
   should be introduced with as little impact as possible and these

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   environments are expected to change over time.

   The MPLS/VPN based CGN architecture solves many of this issues
   related to deploying this technology in existing operator networks.

9.  Acknowledgements

   Thanks to the following people for their participating in integrating
   and testing the CGN environment: Chris Metz, Syd Alam, Richard
   Lawson, John E Spence.

   Additional thanks for the following people for the guidance on IPv6
   transition considerations: John Jason Brzozowski, Chris Donley, Jason
   Weil, Lee Howard, Jean-Francois Tremblay

10.  References

10.1.  Normative References

   [RFC4364]  Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
              Networks (VPNs)", RFC 4364, February 2006.

10.2.  Informative References

   [I-D.donley-nat444-impacts]
              Donley, C., Howard, L., Kuarsingh, V., Berg, J., and U.
              Colorado, "Assessing the Impact of Carrier-Grade NAT on
              Network Applications", draft-donley-nat444-impacts-05
              (work in progress), October 2012.

   [I-D.ietf-behave-lsn-requirements]
              Perreault, S., Yamagata, I., Miyakawa, S., Nakagawa, A.,
              and H. Ashida, "Common requirements for Carrier Grade NATs
              (CGNs)", draft-ietf-behave-lsn-requirements-09 (work in
              progress), August 2012.

   [RFC1918]  Rekhter, Y., Moskowitz, R., Karrenberg, D., Groot, G., and
              E. Lear, "Address Allocation for Private Internets",
              BCP 5, RFC 1918, February 1996.

   [RFC3031]  Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol
              Label Switching Architecture", RFC 3031, January 2001.

   [RFC5969]  Townsley, W. and O. Troan, "IPv6 Rapid Deployment on IPv4
              Infrastructures (6rd) -- Protocol Specification",
              RFC 5969, August 2010.

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

   [RFC6598]  Weil, J., Kuarsingh, V., Donley, C., Liljenstolpe, C., and
              M. Azinger, "IANA-Reserved IPv4 Prefix for Shared Address
              Space", BCP 153, RFC 6598, April 2012.

Authors' Addresses

   Victor Kuarsingh (editor)
   Rogers Communications
   8200 Dixie Road
   Brampton, Ontario  L6T 0C1
   Canada

   Email: victor.kuarsingh@gmail.com
   URI:   http://www.rogers.com

   John Cianfarani
   Rogers Communications
   8200 Dixie Road
   Brampton, Ontario  L6T 0C1
   Canada

   Email: john.cianfarani@rci.rogers.com
   URI:   http://www.rogers.com

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