Scalable Operation of Address Translators with Per-Interface Bindings
RFC 6619

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Internet Engineering Task Force (IETF)                          J. Arkko
Request for Comments: 6619                                      Ericsson
Category: Standards Track                                      L. Eggert
ISSN: 2070-1721                                                   NetApp
                                                             M. Townsley
                                                                   Cisco
                                                               June 2012

 Scalable Operation of Address Translators with Per-Interface Bindings

Abstract

   This document explains how to employ address translation in networks
   that serve a large number of individual customers without requiring a
   correspondingly large amount of private IPv4 address space.

Status of This Memo

   This is an Internet Standards Track document.

   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).  Further information on
   Internet Standards is available in 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/rfc6619.

Copyright Notice

   Copyright (c) 2012 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.

Arkko, et al.                Standards Track                    [Page 1]
RFC 6619                      Scalable NATs                    June 2012

1.  Introduction

   This document explains how to employ address translation without
   consuming a large amount of private address space.  This is important
   in networks that serve a large number of individual customers.
   Networks that serve more than 2^24 (16 million) users cannot assign a
   unique private IPv4 address to each user, because the largest
   reserved private address block reserved is 10/8 [RFC1918].  Many
   networks are already hitting these limits today -- for instance, in
   the consumer Internet service market.  Even some individual devices
   may approach these limits -- for instance, cellular network gateways
   or mobile IP home agents.

   If ample IPv4 address space were available, this would be a
   non-issue, because the current practice of assigning public IPv4
   addresses to each user would remain viable, and the complications
   associated with using the more limited private address space could be
   avoided.  However, as the IPv4 address pool is becoming depleted,
   this practice is becoming increasingly difficult to sustain.

   It has been suggested that more of the unassigned IPv4 space should
   be converted for private use, in order to allow the provisioning of
   larger networks with private IPv4 address space.  At the time of this
   writing, the IANA "free pool" contained only 12 unallocated unicast
   IPv4 /8 prefixes.  Although reserving a few of those for private use
   would create some breathing room for such deployments, it would not
   result in a solution with long-term viability.  It would result in
   significant operational and management overheads, and it would
   further reduce the number of available IPv4 addresses.

   Segmenting a network into areas of overlapping private address space
   is another possible technique, but it severely complicates the design
   and operation of a network.

   Finally, the transition to IPv6 will eventually eliminate these
   addressing limitations.  However, during the migration period when
   IPv4 and IPv6 have to coexist, address or protocol translation will
   be needed in order to reach IPv4 destinations.

   The rest of this document is organized as follows.  Section 2 gives
   an outline of the solution, Section 3 introduces some terms,
   Section 4 specifies the required behavior for managing NAT bindings,
   and Section 5 discusses the use of this technique with IPv6.

Arkko, et al.                Standards Track                    [Page 2]
RFC 6619                      Scalable NATs                    June 2012

2.  Solution Outline

   The need for address or protocol translation during the migration
   period to IPv6 creates the opportunity to deploy these mechanisms in
   a way that allows the support of a large user base without the need