Carrier-Grade NAT (CGN) Deployment with BGP/MPLS IP VPNs
RFC 7289

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Internet Engineering Task Force (IETF)                 V. Kuarsingh, Ed.
Request for Comments: 7289                                 J. Cianfarani
Category: Informational                            Rogers Communications
ISSN: 2070-1721                                                June 2014

        Carrier-Grade NAT (CGN) Deployment with BGP/MPLS IP VPNs

Abstract

   This document specifies a framework to integrate a Network Address
   Translation (NAT) 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 maintain a subscriber-side 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 that 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
   CGN's impact on the network.  This document does not intend to defend
   the merits of CGN.

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/rfc7289.

Kuarsingh & Cianfarani        Informational                     [Page 1]
RFC 7289          CGN Deployment with BGP/MPLS IP VPNs         June 2014

Copyright Notice

   Copyright (c) 2014 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.

Kuarsingh & Cianfarani        Informational                     [Page 2]
RFC 7289          CGN Deployment with BGP/MPLS IP VPNs         June 2014

Table of Contents

   1. Introduction ....................................................4
      1.1. Acronyms and Terms .........................................4
   2. Existing Network Considerations .................................5
   3. CGN Network Deployment Requirements .............................5
      3.1. Centralized versus Distributed Deployment ..................6
      3.2. CGN and Traditional IPv4 Service Coexistence ...............7
      3.3. CGN Bypass .................................................7
      3.4. Routing Plane Separation ...................................8
      3.5. Flexible Deployment Options ................................8
      3.6. IPv4 Overlap Space .........................................9
      3.7. Transactional Logging for CGN Systems ......................9
      3.8. Base CGN Requirements ......................................9
   4. BGP/MPLS IP VPN-Based CGN Framework .............................9
      4.1. Service Separation ........................................11
      4.2. Internal Service Delivery .................................12
           4.2.1. Dual-Stack Operation ...............................14
      4.3. Deployment Flexibility ....................................16
      4.4. Comparison of BGP/MPLS IP VPN Option versus Other
           CGN Attachment Options ....................................16
           4.4.1. Policy-Based Routing ...............................16
           4.4.2. Traffic Engineering ................................17
           4.4.3. Multiple Routing Topologies ........................17
      4.5. Multicast Considerations ..................................17
   5. Experiences ....................................................17