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Versions: 00 01 02

Network Working Group                                  M. Boucadair, Ed.
Internet-Draft                                                  P. Levis
Intended status: Informational                            France Telecom
Expires: January 4, 2010                                        G. Bajko
                                                           T. Savolainen
                                                                   Nokia
                                                            July 3, 2009


IPv4 Connectivity Access in the Context of IPv4 Address Exhaustion: Port
                      Range based IP Architecture
                   draft-boucadair-port-range-02.txt

Status of this Memo

   This Internet-Draft is submitted to IETF 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 January 4, 2010.

Copyright Notice

   Copyright (c) 2009 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
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   Please review these documents carefully, as they describe your rights
   and restrictions with respect to this document.





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Abstract

   This memo proposes a solution, based on fractional addresses, to face
   the IPv4 public address exhaustion.  It details the solution and
   presents a mock-up implementation, with the results of tests that
   validate the concept.  It also describes architectures and how
   fractional addresses are used to overcome the IPv4 address shortage.
   A comparison with the alternative Carrier-Grade NAT (CG-NAT)
   solutions is also elaborated in the document.  The IPv6 variant of
   this solution is described in a companion draft.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
     1.1.  Context  . . . . . . . . . . . . . . . . . . . . . . . . .  4
     1.2.  Tentative Solutions: Overview and Limitations  . . . . . .  4
     1.3.  Contribution of this draft . . . . . . . . . . . . . . . .  6

   2.  Conventions used in this document  . . . . . . . . . . . . . .  6

   3.  Port Range Architecture: Overall Procedure . . . . . . . . . .  7
     3.1.  Introduction . . . . . . . . . . . . . . . . . . . . . . .  7
     3.2.  Basic Principles . . . . . . . . . . . . . . . . . . . . .  8
     3.3.  Applicability Use Cases  . . . . . . . . . . . . . . . . .  9
       3.3.1.  CPE  . . . . . . . . . . . . . . . . . . . . . . . . .  9
       3.3.2.  End Host . . . . . . . . . . . . . . . . . . . . . . .  9
       3.3.3.  Point-to-Point Links . . . . . . . . . . . . . . . . . 10
       3.3.4.  Point-to-Point Tunneled Links  . . . . . . . . . . . . 11

   4.  Retrieving IP Configuration Data . . . . . . . . . . . . . . . 12
     4.1.  Assumption . . . . . . . . . . . . . . . . . . . . . . . . 12
     4.2.  Procedure  . . . . . . . . . . . . . . . . . . . . . . . . 12
       4.2.1.  Overview . . . . . . . . . . . . . . . . . . . . . . . 12
     4.3.  An alternative to avoid DHCP Server modifications  . . . . 13

   5.  Required Modifications . . . . . . . . . . . . . . . . . . . . 16
     5.1.  CPE  . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
     5.2.  End-user Terminals . . . . . . . . . . . . . . . . . . . . 17
     5.3.  Service Provider Infrastructure  . . . . . . . . . . . . . 17
     5.4.  DHCP Server Implementations  . . . . . . . . . . . . . . . 18

   6.  Port Range Router  . . . . . . . . . . . . . . . . . . . . . . 18
     6.1.  Main Function  . . . . . . . . . . . . . . . . . . . . . . 18
     6.2.  Routing Considerations: Focus on IGP . . . . . . . . . . . 19
     6.3.  Binding Table  . . . . . . . . . . . . . . . . . . . . . . 20
     6.4.  Provisioning . . . . . . . . . . . . . . . . . . . . . . . 20
       6.4.1.  Needs  . . . . . . . . . . . . . . . . . . . . . . . . 20



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       6.4.2.  Option 1: CPE-Provisioned PRR  . . . . . . . . . . . . 20
       6.4.3.  Option 2: Provider-Provisioned PRR . . . . . . . . . . 21

   7.  Localization Inside a Service Provider's Domain  . . . . . . . 21

   8.  Fragmentation  . . . . . . . . . . . . . . . . . . . . . . . . 22

   9.  Multicast  . . . . . . . . . . . . . . . . . . . . . . . . . . 23

   10. IGD 2.0  . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

   11. IPSec  . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

   12. ICMP and Other Portless Protocols  . . . . . . . . . . . . . . 25

   13. 6to4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

   14. Protocols not supported by PRR . . . . . . . . . . . . . . . . 26

   15. Comparison with CG-NAT/LSN . . . . . . . . . . . . . . . . . . 26
     15.1. Generic Hurdles  and Focus on Transparency to
           applications which enclose IPv4 address in their
           protocol messages  . . . . . . . . . . . . . . . . . . . . 26
     15.2. Focus on Legal Storage . . . . . . . . . . . . . . . . . . 27
     15.3. Session Handling in CG-NAT . . . . . . . . . . . . . . . . 30
     15.4. Peer-to-Peer applications  . . . . . . . . . . . . . . . . 31

   16. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 31

   17. Security Considerations  . . . . . . . . . . . . . . . . . . . 31

   18. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 32

   19. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 32

   20. References . . . . . . . . . . . . . . . . . . . . . . . . . . 32
     20.1. Normative References . . . . . . . . . . . . . . . . . . . 32
     20.2. Informative References . . . . . . . . . . . . . . . . . . 33

   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 34











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1.  Introduction

1.1.  Context

   It is commonly agreed by the Internet community that the exhaustion
   of public IPv4 addresses is an ineluctable fact.  In this context,
   the community was mobilized in the past to adopt a promising solution
   (in particular with the definition of IPv6).  Nevertheless, this
   solution is not globally activated by Service Providers for both
   financial and strategic reasons.  In the meantime, these Service
   Providers are not indifferent to the alarms recently emitted by the
   IETF particularly by the reports presented within the GROW working
   group (Global Routing Operations Working Group) meetings.

   G. Huston introduced an extrapolation model to forecast the
   exhaustion date of IPv4 addresses managed by IANA.  This effort
   indicates that if the current tendency of consumption continues at
   the same pace, IPv4 addresses exhaustion of IANA's pool would occur
   in 2011, while RIRs'pool would be exhausted in late 2012.  The state
   of the current consumption of public IPv4 addresses is daily updated
   and is available at this URL:
   http://www.potaroo.net/tools/ipv4/index.html.

1.2.  Tentative Solutions: Overview and Limitations

   In order to solve this depletion problem, Service Providers need to
   investigate and enable means to ensure the deployment of their
   service offerings and their delivery to end users.  Two strands may
   be followed:

      (1) Migrate to IPv6:

   IPv6 has been introduced for several years as the next version of the
   IP protocol.  This new version offers an abundance of IP addresses as
   well as several enhancements compared to IPv4 especially with the
   adoption of hierarchical routing (and therefore allows reducing the
   routing tables size).  IPv6 specifications are mature and current
   work within the IETF is related to operational aspects.
   Nevertheless, Service Providers have not largely activated IPv6 in
   their networks yet.

   However, even if a Service Provider activates IPv6, it will be
   confronted with the problem to ensure a global connectivity towards
   nowadays Internet v4.  Mechanisms such as NAT-PT (Network Address
   Translation Protocol Translation) were introduced to ensure the
   interconnection between two heterogeneous realms (i.e., IPv4/IPv6)
   and to ensure a continuity of IP communications (i.e., end-to-end).
   It is out of scope of this document to analyze the hurdles of these



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   solutions.

   Despite the current IPv6 deployment situation, IPv6 is the viable
   alternative to offer IP connectivity services to a large number of
   customers.  From this perspective, Service Providers should avoid
   introducing new functions and nodes which may be problematic when
   envisaging migrating to IPv6.  This critical requirement should not
   be taken into account only during the technical engineering phase,
   but also when elaborating required CAPEX (Capital Expenditure)/OPEX
   (Operational Expenditure) estimation of activating alternative
   schemes to solve or to reduce the impact of the IPv4 address
   exhaustion phenomenon.

   Note that this requires deploying interconnection mechanisms with the
   already existent IPv4 realms.  This cost overhead should be
   considered in transition scenarios.

      (2) Enhance current IPv4 architectures and optimize the assignment
      of IPv4 addresses:

   A first example of the implementation of this option is the
   introduction of a second level of NAT, called Provider-NAT or Carrier
   Grade NAT (CG-NAT).  This node is located in the Service Provider
   domain.  In such option, only private addresses are assigned to end-
   user home gateways, which still perform their own NAT.  The CG-NAT is
   responsible for translating IP packets issued with private addresses
   to ones with publicly routable IPv4 addresses when exiting the domain
   of the Service Provider.

   The introduction of the CG-NAT will have an important impact on the
   applications.  Some services will only work in a degraded mode, some
   will even not work at all (refer to Section 15 for more details about
   encountered hurdles).

   A variant of CG-NAT, called DS-lite, is proposed in
   [I-D.ietf-softwire-dual-stack-lite].  In this mode, only one NAT
   level is maintained but it is located in the service provider's
   network.  Unlike Provider-NAT, IPv6 is used to convey traffic isseud/
   destined from/to customer's device.

   Another example of this second option is the proposal that has been
   made to release IPv4 class E addresses [I-D.fuller-240space]:
   concretely to reclassify 240/4 as usable unicast address space.  The
   rationale of this proposal is that since the community has not
   concluded whether the E block should be considered public or private,
   and given the current consumption rate, it is clear that the block
   should not be left unused.  This proposal requires updating IP-
   enabled equipment so as to treat correctly IPv4 addresses belonging



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   to 240/4 blocks.  These addresses should be routable and announced
   for instance between adjacent Autonomous Systems (ASes) through BGP
   (Border Gateway Protocol) for instance.  An exhaustive study should
   be undertaken to evaluate the economic and technical impact of such
   new policy.  Another alternative is to re-classify class E address as
   private ones [I-D.savolainen-indicating-240-addresses].

1.3.  Contribution of this draft

   This memo specifies an alternative solution to the Double NAT
   architecture which aims at solving the depletion problem as
   encountered by current ISPs.  The proposed solution, called Port
   Range based architecture is session stateless and does not alter the
   various offered services.  The solution presented in this document
   does not require severe modifications to current engineering
   practices as adopted by major Service Providers.  Furthermore, the
   solution is scalable and can be deployed in several variants,
   especially to prepare the migration towards IPv6.

   This draft describes a lightweight architecture that may be deployed
   by Service Providers to offer IP connectivity services to their
   already subscribed customers or to new ones.  This document provides
   an implementation scenario.  Service Providers are free to enforce
   their own engineering rules based on their internal policies and
   available technological means as activated in their IP
   infrastructure.  The solution is flexible enough to be accommodated
   in various contexts.

   The scalability of this solution is similar to current deployed IP
   architectures.  No session-related states are maintained in core
   nodes operated by a given Service Provider.

   This solution can be activated in an end host, CPE (Customer Premises
   Equipment), or any other device able to constraint its source port
   numbers.

   An IPv6 variant of this solution is described in
   [I-D.boucadair-behave-ipv6-portrange].


2.  Conventions used in this document

   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].

   The following abbreviations are used within this document:




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      - ASN GW: Access Service Network Gateway

      - CGN: Carrier Grade Network Address Translator

      - CPE: Consumer Premises Equipment, a device that resides between
      Internet service provider's network and consumers' home network.

      - GGSN :Gateway GPRS Support Node

      - GPRS: General Packet Radio Service

      - PDN GW: Packet Data Network Gateway

      - PDSN: Packet Data Serving Node

      - PRR: Port Range Router


3.  Port Range Architecture: Overall Procedure

3.1.  Introduction

   As an alternative to the Double NAT solution, which suffers from
   several drawbacks, a second alternative is proposed within this
   document.  The motivations for introducing this second alternative
   are as follows:

      - Not to alter current (IPv4-based) services delivery and to not
      impact the introduction of future services;

      - Avoid maintaining sessions states at the core network.
      Stateless solutions are privileged;

      - Ease management functions (including provisioning, configuration
      operations, etc.);

      - Optimise CAPEX and OPEX: As shown latter in this draft, the
      functional requirements to implement the proposed procedure are
      lightweight.  Only slight modifications are required to be
      brought.  Furthermore, the offered services are not impacted.
      Management practices would remain as today.  For example, because
      the solution described in this memo does not handle dynamic NAT
      mappings (contrary to the CG-NAT), the planned maintenance
      operations (replacement of involved network equipment) would not
      impact the delivered services as a CG-NAT-based solution would do;

      - Minor impact on routing and addressing architectures;




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      - Transparent to end-users: The same practices as today's ones
      will remain (e.g., Port forwarding on CPE still possible -provided
      the port is within the allocated Port Range-);

      - Usability easiness;

      - Facilitate functional separation (Service and Network): For
      instance, and unlike CG-NAT, the problem to run SIP-based services
      above a third party IP infrastructure would not be encountered
      with the proposed solution;

      - Ease implementing legal requirements (optimize storage of legal
      data);

      - Ease migration to a long term solution such as IPv6;

   This section focuses only on the IPv4 variant of the solution.  Other
   variants have been defined to integrate IPv6 and offer a global IP
   connectivity services including towards IPv6 realms in a stateless
   manner.  Companion Internet Drafts will be submitted latter.

3.2.  Basic Principles

   The major idea is to assign the same IP address to several end-users'
   devices (e.g., Home Gateways (HGW) embedding NAT, but that could be
   other types of devices embedding NAT) and to constrain the (source)
   port numbers to be used by each device.  In addition to the assigned
   IP address to access IP connectivity services, additional parameters
   are also communicated with the customer's device.  These additional
   parameters indicate which Ports or Port Range(s) is/are assigned to
   the customer's devices.

   In the remaining part of this draft, the above mentioned public
   address is denoted as Primary IP Address.

   For outbound communications, a given HGW proceeds to its classical
   operations except the constraint to control the source port number
   assignment so as to be within the Port Range assigned by its IP
   connectivity Service Provider.  The traffic is then routed inside the
   Service Provider's domain and delivered to its final destination
   (within the service domain or to external domains).

   For inbound communications (i.e., Towards customers attached to the
   Service Provider which has activated the procedure detailed in this
   memo), the traffic is trapped by a dedicated function called: Port
   Range Router (PRR).  This function may be embedded in current routers
   or hosted by new nodes to be integrated in the IP infrastructure of
   these Service Providers.  Appropriate routing tuning policies are



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   enforced so as to drive the inbound traffic to cross a PRR (see
   Section 6 for more details).  Particularly, each PRR correlate the
   Primary IP Address and information about the allowed port values with
   a specific identifier called: routing identifier (e.g., secondary
   IPv4 address, IPv6 address, point-to-point link identifier, etc).
   This routing identifier is used to route the packets to the suitable
   device among all those owning the same IP address (See Section 6.1).

   Note that for some reasons (e.g., Ease implementation of port-driven
   RPF (Reverse Path Forwarding) checking, anti-spoofing techniques,
   etc.), outbound traffic may be constrained to invoke the PRR
   function.  This feature for outbound packets is considered as an
   engineering option.  Service Providers are free to enforce it or not.

3.3.  Applicability Use Cases

   The following sub-sections provide a non exhaustive list of the port
   range solution applicability use cases.  Other scenarios may be
   envisaged.

3.3.1.  CPE

   For deployment considerations and reduction of impact on terminals,
   the recommended scenario (in the context of DSL-type service
   offerings) of the deployment of the solution is a Provider
   provisioned CPE.  This scenarios hides the connectivity solution and
   its associated addressing architecture.  Machines behind the CPE
   continue to behave as today.  No modification is required on end
   hosts.

3.3.2.  End Host

   When a host, which is capable of an IP address and a port range, but
   some of the applications on the host may have trouble using those
   addresses (e.g., they require a specific port to operate), as an
   implementation choice, the host may hide the port restricted nature
   of the allocated address by implementing an internal NAT as
   illustrated in the figure:













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      Host
        +---------------------+
        +  Application        +
        +    |                +
        +    | IPv4p +-----+  +  IPv4 address and a port range
        +    |-------| NAT |  +---------------------------------
        +            +-----+  +
        +                     +
        +---------------------+


                     Figure 1: Internal NAT in a host

3.3.3.  Point-to-Point Links

   In point-to-point links it can be assumed that there are only two
   communicating parties on the link, and thus IP address collisions are
   easy to avoid.

   In wireless cellular networks host attached to an access router, such
   as 3GPP PDN GW or WiMAX ASN GW , over a point-to-point link providing
   layer 2 IPv4 transport capability.

   In order to be able to allocate an IP address together with a port
   range to a host, the access router needs to implement DHCP server or
   at least act as a DHCP relay or DHCP proxy , while a DHCP server
   exists in the backend.  These setups are illustrated in the following
   figure.

                                       +--------+      |
         3GPP  ---Point to Point link--| 3GPP   |------|
         host     <-IPv4 EPS bearer--> | PDN GW |      |
                                       +--------+      |
                                                       | IPv4 Internet
                                       +--------+      |
         WiMAX ---Point to Point link--| WiMAX  |------|
         host     <-----IPv4 CS------> | ASN GW |      |
                                       +--------+      |

                  Figure 2: Point-to-point physical links

   As each host is attaching to the access router with an individual
   link, both modified and unmodified hosts can be supported
   simultaneously.  This enables incremental deployment of modified
   hosts that are supporting public IPv4 address conservation by using
   DHCP to assign IPv4 address and a port range, while continuing to
   support the legacy hosts using DHCP as currently specified.




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   In this scenario, IPv6 addresses can be used in parallel with any
   IPv4 address, therefore no tunneling is necessary.

   If PPP is used, port restricted IPv4 address can also be configured
   in PPP IPCP option as described in
   [I-D.boucadair-pppext-portrange-option].

3.3.4.  Point-to-Point Tunneled Links

   From DHCP point of view, tunneled link scenario does not differ very
   much from L2 point-to-point links as described in the previous
   section, although there are general concerns regarding tunnels (e.g.,
   decreased MTU).

   The tunnel is established between a host (or a CPE) and a tunnel
   endpoint in the host Operator's network.  In different scenarios, the
   tunnel endpoint may be placed at different locations.  The tunnel
   endpoint can be at the first hop router such as 3GPP2 PDSN or 3GPP
   PDN-GW, or farther off in the network.  In one scenario, the tunnel
   endpoint can be the CGN of DS-Lite
   [I-D.ietf-softwire-dual-stack-lite].

   These example setups are illustrated in the following figure.
                                   Tunnel endpoints,
                                  implementing DHCPv4
                                  server/relay/proxy

                                    +-------------+
        Host ====IPv4 over IPv6==== | 3GPP2       |      |
             <---PPP & IPv6CP ----> | PDSN        |------|
                 (point-to-point)   +-------------+      |
                                                         |
                                    +-------------+      |
        Host ====IPv4 over IPv6==== | 3GPP        |------| IPv4 Internet
             <--IPv6 PDP context--> | GGSN        |      |
                (point-to-point)    +-------------+      |
                                                         |
                                    +-------------+      |
        Host ====IPv4 over IPv6==== | IETF        |------|
             <---- IPv6-only -----> | DS-Lite CGN |      |
                   network          +-------------+

    Figure 3: Point-to-point links as IPv4 over IPv6 tunnels over three
                            different accesses

   Having the tunnel endpoint at the first hop router can be beneficial
   in setups where arrangement of native dual-stack transport for the
   last mile is not feasible or cost-effective approach.  This can be



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   the case e.g., in 3GPP networks, prior 3GPP Release-8, where a PDP
   context is capable of transporting only IPv4 or IPv6 packets, and for
   dual-stack access two parallel PDP contexts are required.

   For networks which use IP(v6)CP to configure IPv4 and IPv6 addresses
   to the host, allocating an IPv4 address and a port range to the host
   to prevent running out of available IPv4 addresses, can also be a
   feasible solution.  In these deployment scenarios, IPv6CP would be
   used to configure an IPv6 address to the host.  The host would then
   set up the tunnel and use the DHCPv4 extensions defined in this
   document to request an IPv4 address together with a port range.
   Examples of such networks include 3GPP2 and BRAS.


4.  Retrieving IP Configuration Data

4.1.  Assumption

   In the context of this section, it is assumed that DHCP (Dynamic Host
   Configuration Protocol, [RFC2131]) is used to convey IP connectivity
   information.  Other alternatives, such as PPP (Point-to-Point
   Protocol, [RFC1661] and [I-D.boucadair-pppext-portrange-option]), may
   be used.  The procedure described in this section is only an
   illustration example.  It may be adapted so as to be able to apply in
   other technological contexts.

4.2.  Procedure

4.2.1.  Overview

   At a bootstrapping phase, a given HGW issues a DHCP_DISCOVER message.
   This message is sent in broadcast.  This message can be relayed by a
   DHCP Client Relay or be received directly by a DHCP Server.  Once
   this message is received by a DHCP Server, this latter answers the
   requester by a dedicated DHCP_OFFER message containing a
   configuration offer.

   The exchange which intervenes is illustrated in the following figure:













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   +-----+                     +-------------+
   | HGW |                     | DHCP Server |
   +-----+                     +-------------+
      |                               |
      |      (1) DHCP DISCOVER        |
      |------------------------------>|
      |                               |
      |                               |
      |       (2) DHCP OFFER          |
      |<------------------------------|
      |                               |

                         Figure 4: DHCP Call Flow

   A DHCP OFFER message encloses a set of IP-related information so as
   to access IP connectivity service.  Particularly, it includes an IP
   address together with a new DHCP option, see:
   [I-D.bajko-pripaddrassign].

   Additional information may be included in the DHCP offer.

   The use of Port Mask DHCP sub-option (similar to subnet mask) makes
   it possible to extend the notion of Port Range with non-continuous
   values, for the sake of flexibility.

   A Port Range is then a set of ports that all have in common a subset
   of pre-positioned bits.

   Once a Port Range information is received by a HGW, it constrains its
   NAT operations to the provisioned range.  The number of customers to
   which an ISP can assign the same IP address depends on the number of
   allowed port numbers per user.  Thus, if N bits are used to build the
   Port Mask, 2^N customers can be provided with the same IP address.
   For example: If N == 3, then the Service Provider multiplies by 8 its
   capacity in term of number of customers to which the connectivity
   service may be delivered.

   In the remaining part, Port Mask and Port Range are used
   interchangeably.

4.3.  An alternative to avoid DHCP Server modifications

   To avoid alteration of already in place DHCP servers, this section
   presents an alternative to implement Port Range assignment procedure.
   This alternative relies on DHCP Relay Clients or DHCP proxies and not
   on DHCP servers.  These latter are kept unchanged.  Their main
   function is to assign an available IP address.  This address is
   assumed to be routed inside the Service Provider domain.



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   DHCP proxies, in cooperation with the PRR, maintains a set of pre-
   assignments based on a pre-provisioned Service Provider policy
   regarding how to build Port Ranges.  As an example, if the
   implemented policy is to assign the same IP address to 4 customers,
   then 4 Port Ranges per IP address are statically built and then
   assigned to customers upon request.

   In this context, DHCP proxies do not relay any IP assignment request
   until all available Port Ranges are allocated.

   Figure 5 and Figure 6 provide an example of this option.  In this
   example, CPE-1 and CPE-2 are two CPEs of two distinct customers.

   CPE-1 sends first its DHCP DISCOVER message.  This message is
   received by the DHCP proxy.  Upon receipt, a lookup on available IP
   address and Port Range is achieved by the DHCP proxy.

   Since no IP address is available, a DHCP DISCOVER message is
   forwarded to the DHCP Server.  A DHCP OFFER is then sent back.  This
   offer is trapped by the DHCP proxy.

   The assigned IP address is retrieved and a pre-allocation of a Port
   Range is achieved.  The offer is then updated with the Port Range
   Information and then relayed to CPE-1.

   The remaining operations are the same operations as current DHCP
   exchanges.
























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   +-----+              +-----+           +--------+            +------+
   |CPE-1|              |DHCP |           |Binding |            |DHCP  |
   |     |              |proxy|           |Table   |            |Server|
   +-----+              +-----+           +--------+            +------+
      |  (1)DHCP DISCOVER  |                  |                    |
      |------------------->|                  |                    |
      |                    |(2) Check if there|                    |
      |                    |  is an available |                    |
      |                    |    IP @ and a    |                    |
      |                    |    Port Range    |                    |
      |                    |----------------->|                    |
      |                    |                  |                    |
      |                    |(3) No Available @|                    |
      |                    |                  |                    |
      |                    |<-----------------|                    |
      |                    |                  |                    |
      |                    | (4) DHCP DISCOVER|                    |
      |                    |-------------------------------------->|
      |                    |              (5) DHCP OFFER(IP-Pub-1) |
      |                    |<--------------------------------------|
      |                    | (6) DHCP REQUEST (IP-Pub-1)           |
      |                    |-------------------------------------->|
      |                    |              (7) DHCP ACK(IP-Pub-1)   |
      |                    |<--------------------------------------|
      |                    |                  |                    |
      |                    |(8)Add IP-Pub-1   |                    |
      |                    |  to Ports Range  |                    |
      |                    |    allocation,   |                    |
      |                    |and pre-assign a                       |
      |                    | Port Range to CPE1                    |
      |                    |----------------->|                    |
      |(9)DHCP OFFER(IP-Pub-1, PR1)           |                    |
      |<-------------------|                  |                    |
      |                    |                  |                    |
      |(10)DHCP REQUEST(IP-Pub-1, PR1)        |                    |
      |------------------->|                  |                    |
      |                    |(11) Assign PR1 to|                    |
      |                    |       CPE1       |                    |
      |                    |----------------->|                    |
      |(10)DHCP ACK(IP-Pub-1, PR1)            |                    |
      |------------------->|                  |                    |
      |                    |                  |                    |

                          Figure 5: First Example

   If CPE-2 requests an IP address, it issues a DHCP DISCOVER message.
   This message is not relayed to the DHCP Server.  A lookup request is
   executed by the DHCP proxy to check if an IP address and a Port Range



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   are available to be assigned.  In this example, a positive answer is
   sent to the DHCP proxy.  A DHCP Offer is then sent to CPE-2 as
   illustrated in Figure 6.

   +-----+              +-----+           +--------+            +------+
   |CPE-2|              |DHCP |           |Binding |            |DHCP  |
   |     |              |proxy|           |Table   |            |Server|
   +-----+              +-----+           +--------+            +------+
      |  (1)DHCP DISCOVER  |                  |                    |
      |------------------->|                  |                    |
      |                    |(2) Check if there|                    |
      |                    |  is an available |                    |
      |                    |    IP @ and a    |                    |
      |                    |    Port Range    |                    |
      |                    |----------------->|                    |
      |                    |                  |                    |
      |                    |(3) OK (IP1)      |                    |
      |                    |                  |                    |
      |                    |<-----------------|                    |
      |                    |                  |                    |
      |                    |                  |                    |
      |                    |(4) Allocate IP1  |                    |
      |                    |and Pre-assign a  |                    |
      |                    |Port Range to CPE2                     |
      |                    |----------------->|                    |
      |(9)DHCP OFFER(IP-Pub-1, PR2)           |                    |
      |<-------------------|                  |                    |
      |                    |                  |                    |
      |(10)DHCP REQUEST(IP-Pub-1, PR2)        |                    |
      |------------------->|                  |                    |
      |                    |(11) Assign PR2 to|                    |
      |                    |       CPE2       |                    |
      |                    |----------------->|                    |
      |(10)DHCP ACK(IP-Pub-1, PR2)            |                    |
      |------------------->|                  |                    |
      |                    |                  |                    |

                         Figure 6: Second Example


5.  Required Modifications

5.1.  CPE

   Above, we have quoted the case of Home Gateway but the solution can
   fit to any kind of Customer Premises Equipment (CPE).

   In order to activate the aforementioned solution, slight



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   modifications are required to be supported by CPEs.  Concretely, CPEs
   MUST be able to constrain their NAT operations and to use only source
   port numbers within the allocated Port Range.  If an IP packet is
   received by a given Port Range-enabled CPE, with a destination port
   number outside the assigned Port Range, the packet MUST be discarded.

   Moreover, Port Range-enabled CPEs MUST be able to enforce
   configuration data received from the Service Providers so as to
   constrain its Port Range.  More particularly, if DHCP is used to
   convey configuration data, a particular DHCP option (to be assigned
   by IANA) is to be supported by that CPE.

   According to the enforced routing identifier mode, a de-encapsulation
   function MAY be required to be supported.

5.2.  End-user Terminals

   In some deployment scenarios (e.g., mobile), end-hosts should be
   updated.  Concretely, end-hosts MUST be able to constrain their
   source port numbers and to use only source port numbers within the
   allocated Port Range.  If an IP packet is received by a given Port
   Range-enabled end-user terminal, with a destination port number
   outside the assigned Port Range, the packet MUST be discarded.

   Moreover, Port Range-enabled terminals MUST be able to enforce
   configuration data received from the Service Providers so as to
   constrain its Port Range.

   According to the enforced routing identifier mode, a de-encapsulation
   function MAY be required to be supported.

5.3.  Service Provider Infrastructure

   The IP infrastructure of a given IP Service Provider is maintained
   slightly unchanged when deploying the Port Range architecture based
   solution.  Only, a new function is introduced.  This new function is
   denoted as PRR.  This function is responsible for routing packets to
   the appropriate end-user's device among those to which the same IP
   address is assigned by the Service Provider.  This operation is
   denoted as Port-Driven Routing operation since the destination IP
   address is not sufficient to handle routing operations and the
   information related to destination port is also required.

   Except the PRR, all classical operations and practices remain as
   today's ones.

   A PRR can be stand-alone server, or it can be hosted into other boxes
   such existing routers, PDN GW, ASN GW, etc.



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5.4.  DHCP Server Implementations

   In case DHCP is used to convey IP connectivity information to
   customers' devices, DHCP server implementations may be modified
   accordingly.  Indeed, DHCP server implementation should be modified
   so as to be able to support additional options such as Port Range
   DHCP option.  The DHCP server assignment policy can be tuned by the
   Service Provider.  A given Service Provider can provision its DHCP
   server with the Port Range to be allocated to end users' devices.

   A second alternative to assign Port Ranges is described in
   Section 4.3.  This alternative does not require any modification of
   the DHCP Server.  Nevertheless, new changes are required to be
   supported by DHCP proxies.


6.  Port Range Router

6.1.  Main Function

   As stated above, the main function implemented by a PRR is a port-
   driven routing.  In order to implement the port-driven routing, the
   following operations are achieved by a given PRR:

   In order to implement the port-driven routing, the following
   operations are achieved by a given PRR:

   1.  It retrieves both destination IP address and destination port
       number.

   2.  Based on this couple, the PRR consults its binding table and
       retrieves the routing identifier.

   Several modes may be envisaged to assign a routing identifier to be
   used as a deterministic discriminator to unambiguously identify a
   device among all those having the same IP address.

   Hereafter are provided some implementation alternatives:

   1.  If a Secondary-IP address is used as the routing identifier: the
       PRR consults its binding table and retrieves the corresponding
       Secondary-IP address associated with a (Destination IP, Port
       Mask).  Once retrieved, the PRR encapsulates the original packets
       in an IPv4 one with a destination IP address equal to
       Secondary-IP.  This packet is then routed according to
       instantiated IGP (Interior Gateway Protocol) routes.  Once
       received by the CPE, a de-encapsulation operation is achieved.
       The original packets is then treated and handled locally.  If



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       destination port of that packet is within the Port Range of that
       CPE, and depending on the local NAT implementation, the packet
       may be accepted and then proceed to classical NAT operation.
       Otherwise, the packet is dropped.  Note that:

       A.  The scope of the secondary address is limited to the access
           segment

       B.  The secondary IP address may be an IPv6 address

   2.  Instead of encapsulation, and if source routing is supported, an
       explicit route is forced.  A loose route is indicated in the
       packets.  This loose route contains at least Secondary-IP.  The
       routing of the resulting packet will be based on that address and
       not the destination one.  The packet will be then received by the
       CPE with that Secondary-IP address.  Then, the CPE will route the
       packet based on the final destination IP address.  Since that
       address is also an IP address of that CPE, the packet is handled
       locally.  The remaining operations are similar to the ones
       implemented by current CPEs.

   3.  If disjoint routes have been pre-installed so as to unambiguously
       identify the targeted device among all those having the same IP
       address, the PRR consults its binding tables and retrieves the
       index of the route corresponding to that (Destination IP, Port
       Mask) pair.  The original packet is then sent over that route.
       Since the routes are disjoint, the packet will be received by the
       targeted CPE.  A example is the case where the PRR and the CPEs
       are directly linked by Ethernet, the route is then identified by
       the Ethernet MAC address of the CPE.

   4.  The routing identifier can also be the identifier of the L2
       point-to-point link

   As for inbound, a new operation is introduced in the path, this
   operation is a port-driven operation with no modification of the
   original packet.  Further evaluation should be undertaken so as to
   assess the impact of this operation.

   The performance experienced by outbound packets is not impacted since
   no alteration of the issued packets is to be enforced in the path.
   The experienced QoS (Quality of Service) is then the same as the
   currently deployed one.

6.2.  Routing Considerations: Focus on IGP

   A PRR is inserted in the inbound path in order to execute a port-
   driven routing.  This constraint is translated into an IGP one.



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   Indeed, a given PRR MUST advertise in IGP the primary IP addresses it
   handles.  Doing so, all inbound packets will cross that PRR.

   In case IPv4 Secondary-IP addresses are used to uniquely identify a
   CPE among all those having the same Primary-IP address, IPv4
   Secondary-IP addresses MUST NOT be routable addresses inside core
   network.  These addresses MUST NOT be reachable from the Internet.
   An example of the scope of those addresses is up to the frontier of
   an IP access POP (Point of Presence).

6.3.  Binding Table

   In order to implement port-driven routing operations, a PRR maintains
   a binding table which is a collection of entries correlating (IP
   address, Port Mask) with a routing identifier.

   This table should not be confused with the NAT table as maintained by
   a CG-NAT.

6.4.  Provisioning

6.4.1.  Needs

   In order to be able to treat received packets and then to proceed to
   port-driven routing, a PRR MUST be provisioned appropriately.
   Concretely, and as stated above, a given PRR needs to maintain a
   binding table which correlates a destination IP address and a Port
   Mask with a routing identifier (such as a secondary IPv4 address,
   IPv6 address, routing index, MAC address, PPP session identifier,
   etc.).  This binding table can be provisioned either by the Service
   Provider (owing to an internal interface) or by the CPE itself once
   IP connectivity information has been received from the service
   platform.

   These two options are described hereafter.  Service Providers are
   free to implement the option which meets its internal engineering
   policies.

6.4.2.  Option 1: CPE-Provisioned PRR

   Once its IP connectivity configuration is retrieved owing to a
   dedicated means such as DHCP, a given CPE enforces this new
   configuration.  Particularly, the new received information may
   contain the following information:

   {Primary-IP, Port Mask, Default_PRR, Routing Identifier}

   In case the adopted method for the routing identifier (mentioned in



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   Section 6.1) is a Secondary-IP address, a message is issued by the
   CPE towards its Default PRR.  This message notifies that PRR about
   the new association: i.e., (Primary-IP, Port Mask) with Secondary-IP.
   This notification is achieved owing to a new message denoted as BIND.
   Once received by the PRR, an ACK message must be sent as response.
   If no ACK message is received, the CPE re-transmits its BIND message.

   The procedure is sketched in the following figure:


   +-----+                         +-----+
   | HGW |                         | PRR |
   +-----+                         +-----+
      |                               |
      |         (1) BIND              |
      |------------------------------>|
      |                               |
      |                               |
      |           (2) ACK             |
      |<------------------------------|
      |                               |

                 Figure 7: Example of CPE-provisioned PRR

   Authentication means may be required to prevent creating hostile
   bindings.

6.4.3.   Option 2: Provider-Provisioned PRR

   Here, the provisioning of PRR binding table is undertaken by the
   Service Provider owing to the activation of appropriate management
   interfaces.  These interfaces are internal to Service Provider's
   domain and are not visible to end-users.  Exchanges between the PRR
   and the management realms are operated by the Service Provider.  An
   implementation scenario of this option, is that once the DHCP server
   has assigned an IP address together with a Port Range a dedicated
   message is issued towards a PRR so as to instantiate a new entry in
   the binding table of that PRR.  The entry can be refreshed or dropped
   once required.

   In both options, the structure of the binding tables and the state
   machine of the PRR are identical.


7.  Localization Inside a Service Provider's Domain

   Each service Provider is free to adopt its internal policies for the
   deployment of PRRs.  Nevertheless, we recommend deploying those nodes



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   at access segment in order not to significantly impact end-to-end
   routing optimization.  A PRR function can be embedded in an access
   router, a DSLAM, etc.

   Several engineering options may be enforced:

   o  A given IP address is shared between several customers located in
      the same access POP: In this scenario, only access routers should
      be updated to support a PRR function.  Doing so, communication
      (more precisely IGP routes) between the customers located in the
      same POP are optimised.

   o  Re-use the same IP address in several access POP and assign the
      same port range to all customers of the same POP: In this
      configuration, a given IP address is assigned to a single customer
      per POP.  For intra-domain communications, and for optimisation
      purposes, all access routers should enable a PRR function.  A far
      head router in the network should be activated to route inter POP
      traffic.


8.  Fragmentation

   In order to deliver a fragmented IP packet to its final destination
   (among those having the same IP address), the PRR should activated a
   dedicated procedure which described hereafter:

   1.  Check if the received packet is a fragment: ((MF == 1 && Fragment
       Offset == 0) || (Fragment Offset != 0)), else apply the classical
       PRR routing procedure;

   2.  Check if this fragment is the first one (MF == 1 && Fragment
       Offset == 0)

          2.1.  In addition to the information retrieved to enforce port
          range routing, retrieve the source IP address and packet
          identifier.  A fragmentation entry is instantiated.  A timer
          (referred to as fragmentation timer) is associated with this
          entry.  A clean up procedure is achieved when the timer
          expires.

          2.2.  Retrieve the binding entry to be used to route this
          first fragment.  A pointer to this entry is added to the
          fragmentation entry.  A fragmentation entry includes:
          destination IP address, source IP address, Identifier, binding
          entry identifier and timer.





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   3.  Check if this fragment is not the first one (Fragment Offset !=
       0)

          3.1.  Retrieve the source IP address, destination IP address
          and Identifier;

          3.2 Check if an entry having the same source IP address,
          destination IP address and Identifier is instantiated in the
          fragmentation table



             3.2.1 If yes, retrieve the binding entry pointer from the
             fragmentation table.  Use the corresponding entry to route
             the fragment.

             3.2.1 If not (fragments are not received in the order),
             launch a timer (which value is small than the fragmentation
             timer).  This timer is referred to as fragmentation order
             timer.  Upon expire of this timer, go to Step 3.2.  This
             step is repeated two or three times.  If it fails, the
             fragment is dropped.

   Note that it is recommended to use a PMTUD path discovery mechanism
   (e.g., [RFC1191]).

   Security issues related to fragmentation are out of scope of this
   document.  For more details, refer to [RFC1858]


9.  Multicast

   In the previous sections, only unicast considerations have been
   elaborated.  This section focuses on the impacts on multicast
   mechanisms and services when a Port Range based solution is
   activated.

   Since the proposed solution does not require any modification on the
   core network of a given service provider / IP network provider,
   protocols to build and maintain multicast trees (e.g., PIM-SM
   [RFC4601], M-OSPF [RFC1584]) can be activated without any
   modification.  Concretely, current multicast configurations on core
   routers and nodes can be applied without any adaptation.

   As far as multicast group membership is concerned, classical
   procedures, e.g., IGMPv2 [RFC2236], or IGMPv3 [RFC3376], may be
   impacted.




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   Concretely:

   1.  If a secondary IP address (see Section 6.1) is used, the
       subscription to a multicast group can be done using this address.
       Thus, IGMP operations to receive traffic (i.e., IGMP requests)
       are not impacted and multicast traffic can be forwarded to the
       subscribed hosts;

   2.  If the shared IP address is used to issue IGMP requests,

       A.  If distinct public IP addresses are assigned to each customer
           which device is attached to the same multicast router:
           classical IGMP operations are valid.  No adaptation is to be
           enforced.  Multicast traffic can be forwarded to each
           subscribed users without ambiguity.

       B.  If a same public IP address is assigned to several customers
           which devices are attached to the same multicast router: the
           attached multicast router should correlate the request source
           with the binding table to unambiguously forward the multicast
           traffic to the appropriate subscribed user.  More precisely,
           IGMP states should be updated to include the routing
           identifier to be used to forward traffic to the subscribed
           host.  Appropriate means to uniquely distinguish the source
           of IGMP request among those having the same IP address should
           be implemented.

           +  To avoid the modification of IGMP, several virtual router
              instances can be instantiated into the same physical node.
              Each virtual router manages only distinct IP addresses.
              This configuration is similar to the bullet a.

   In addition to these considerations, a hurdle can be encountered when
   using IGMPv3.  Indeed, IGMPv3 messages can specify specific sources
   to be used to be excluded.  If a shared IP address is assigned to
   those sources, traffic issued by other sources having the same IP
   address can be impacted.  This scenario is not viable in current
   multicast deployments since the source of multicast traffic is under
   control of a service provider (e.g., head ends in the context of IP
   TV service offering) and a not shared IP address would be assigned to
   head ends.


10.  IGD 2.0

   Version 2.0 of IGP specification recommends the usage of a new method
   called AddAnyPortMapping() instead of AddPortMapping().  This new
   specification will ease the deployment of shared IP addresses.



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11.  IPSec

   Even if IPSec is not deployed for mass market, impacts of solutions
   based on shared IP addresses should be evaluated and assessed.
   [RFC3947] proposes a solution to solve complications issues
   documented in [RFC3715].  Below is described an analysis of the
   applicability of [RFC3947] in the context of this solution.

   Indeed,[RFC3947] (Section 4, Changing to New Ports), specifies that
   if an IKE peer responder is behind a port translating NAT, the
   initiator is allowed to use a different port than 4500 to contact it.
   The initiator will have to determine which ports to use by contacting
   another server or by out of band procedure .  Once the initiator
   knows which ports to use to traverse the NAT, generally something
   like UDP (4500, Z), it initiates using these ports.

   In the case both IKE initiator and responder peers are behind a Port
   translating NAT, the changing port can be summarized as follows:

Init addr     CPE Pub1. addr          PRR_CPE Pub. addr          Resp. addr
        v              v                 v            v   PRR          v

 Initiator ---------->CPE-----------------> PRR ---------->CPE----------->Responder
           ^          NAT               ^          ^      NAT    ^
           |                            |          |             |
Init addr, PRR_CPE.Pub addr UDP(4500,Z) |          |   CPE Pub1 addr, Resp.addr (1234,4500)
                                        |          |
                           CPE Pub1 addr, PRR_CPE.Pub addr UDP(1234,Z)


12.  ICMP and Other Portless Protocols

   The multiplexing of IP flows in PRR is based on the port numbers used
   by transport layer protocols such as TCP, UDP, SCTP, and DCCP.
   However, the protocols not containing port numbers need special
   handling in order to be multiplexed correctly.

   As for ICMP messages, identifier field may be used as port number.
   The value of this field should be selected from the assigned port
   range value.  This approach has a limit when both the source and
   destination are assigned with a shared IP address.


13.  6to4

   A host utilizing 6to4 [RFC3056] with port restricted IPv4 addresses
   must pick the 16-bit "SLA ID" value for the 6to4 prefix(es)
   construction from the pool of allocated port values.  The



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   multiplexing gateway must then multiplex 6to4 traffic based on "SLA
   ID" value as it would multiplex plain IPv4 traffic based on port
   values. i.e., for incoming packets the gateway shall look at the
   destination IPv4 address and the "SLA ID"-field from tunneled IPv6
   packet's destination IPv6 address, and then select the right route as
   it would have picked the port number from a transport layer header.


14.  Protocols not supported by PRR

   The case where Port Range Router is not able to multiplex a protocol
   is similar to a case where middle box, such as firewall or NAT,
   blocks traffic it is not able or willing to pass trough.  The
   application is recommended to fallback to UDP encapsulation often
   used for NAT traversal, for which gateway is able to perform
   multiplexing.


15.  Comparison with CG-NAT/LSN

15.1.  Generic Hurdles  and Focus on Transparency to applications which
       enclose IPv4 address in their protocol messages

   When deploying a Double NAT scenario, several hurdles will be
   encountered by Service Providers.  Examples of these hurdles are as
   follows:

   o  End-users won't be able to configure their own port forwarding
      policies anymore, whilst with the Port Range solution, the user
      can still configure port forwarding (provided the port is within
      the allowed range).

   o  Need to activate a second ALG (Application Level Gateway) at the
      core network for some applications (e.g., SIP (Session Initiation
      Protocol, [RFC3261]);

   o  Problems to run servers behind middleboxes with private addresses;

   o  Complication to enable inbound access;

   o  Performance issues (e.g., maintaining NAT entries by frequent
      (every 30s for instance) keep-alive messages is a real killer for
      battery powered devices);

   o  Interference between the service and network layers: The delivery
      of some services (e.g., SIP, DNS (Domain Name Service, [RFC1034]),
      and FTP (File Transfer Protocol, [RFC3659])) will require the
      knowledge of the underlying network engineering characteristics



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      (i.e., Presence of intermediate CG-NAT boxes).  If distinct
      administrative entities are managing the high-level services and
      the underlying IP infrastructure, critical problems for the
      current Internet business model will be raised.

   Besides these generic hurdles, let's consider the ones that may arise
   when delivering SIP-based calls in the presence of CG-NAT boxes.
   Concretely, the following constraints should be followed:

   o  The SIP-based Service Provider should be aware about the
      underlying IP infrastructure so as to implement appropriate ALGs
      (Application Level Gateway).  At least two modifications of SIP
      messages should be applied: The first one at the Home NAT and the
      second one at the CG-NAT.  If no such ALG is enabled, no
      communication may be established.  This constraint is heavy since
      it assumes that the same administrative entity administers both
      service and network infrastructures.

   o  NAT mapping entries at the CG-NAT should be maintained by keep-
      alive packets so as to be able to deliver incoming messages to
      customers' devices located behind the CG-NAT.

   o  Media flows may encounter some problems to be delivered since RTP
      (Real Time Transport Protocol, [RFC1889]) ports may not be opened.

   The introduction of CG-NAT nodes may impact heavily the delivery of
   SIP-based services.

   With a Port Range approach, nothing is changed with regard to the
   behavior of a today CPE with NAT: a SIP ALG can be quite easily
   implemented to take care of swapping the embedded IP address and port
   number in the messages to reflect the outbound IPv4 address and port
   of the CPE.  On the contrary, running a SIP ALG instance inside the
   Carrier-Grade NAT for each SIP client may turn out to be very
   complex.  Therefore, with the Port Range approach, SIP-based services
   are not altered compared to current practices when a CG-NAT is
   present in the path.  The same mechanisms as today have to be
   deployed without any additional constraint nor impact.

   Consequently, SIP-based services are not altered and complexity not
   increased.

15.2.  Focus on Legal Storage

   Most National Regulatory Authorities (NRA) require that ISPs provide
   the identity of a customer upon request of the authorities.  This
   requirement is usually denoted as Legal Storage.  In order to
   implement this requirement, Service Providers have deployed



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   appropriate infrastructures including memory storage and interface to
   their Information Systems.  Due to the continuous increase of traffic
   exchanged between end users, the amount of data stored by Service
   Providers would be also impacted if data relevant to all the sessions
   were to be stored.  This is considered as a critical issue by Service
   Providers.

   When deploying a new IP architecture or when modifying the currently
   deployed ones, Service Providers should be able to assess its impact
   on their Legal Storage infrastructures.  Concretely, and because of
   the presence of NAPT function the knowledge of the source port number
   (simply referred to as port number), along with the source public IP
   address (simply referred to as public IP address), is mandatory to be
   able to retrieve the appropriate customer (or user) which is
   concerned by a given flow.  This implies that all NAT mapping
   information is to be stored by a given ISP during the whole legal
   duration (one year in many countries).

   Concretely, and because of the presence of NAPT function (in the CG-
   NAT), the knowledge of the source port number (simply referred to as
   port number), along with the source public IP address (simply
   referred to as public IP address), is mandatory to be able to
   retrieve the appropriate customer (or user) which is concerned by a
   given flow.  This implies that all NAT mapping information is to be
   stored by a given ISP during the whole legal duration (one year in
   many countries).

   When a CG-NAT is deployed, a given Service Provider must store legal
   information of the mapped addresses in form of the following tuple:

   {Public IP address - Public Port - Private IP address - Private port
   - protocol - date and hour of the beginning of address/port
   allocation - duration of this allocation (or date and hour of the
   allocation end)}.

   Note that to actually find the identity of the appropriate customer
   which is concerned by a given IP flow, a given ISP must also store
   the mapping between the private IP address and the customer
   identification.

   As for the Port Range based approach, the required information to be
   stored is the following tuple (called in the remaining part tuple
   with Port Range):

   {Public IP address - Port Range - protocol - customer identification
   - date and hour of the beginning of the Public IP address and Port
   Range allocation - duration of this allocation (or date and hour of
   the allocation end)}.



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   The length of this tuple with Port Range is about:

   4 + 3 (2 for the Port Range pattern + 1 for the length) + 20
   (customer identification) + 8 (date/time begin) + 8 (date/time end) =
   43 bytes.

   The Port Range is expected to be allocated for the same duration as
   the IP address, namely for a reasonable term (e.g., more than 24
   hours conforming to current practices of IP address assignment).
   Thus, with regard to the nowadays situation, the additive information
   to be stored is only the Port Range.

   The allocation of Public IP address and Port Range is expected to be
   made for a reasonable term (e.g., more than 24 hours) as the current
   practices for the assignment of IP addresses.

   In order to illustrate the volume of required data to be stored by
   Service Providers,let's consider the following figures:

   o  1000 CPEs

   o  100 new sessions per 10 minutes per CPE (optimistic, it may be
      more)

   o  each CPE traffics during 6 hour a day

   o  the public address and Ports Range change each day (changing these
      parameters may be even less frequent)

   The amount of data to be stored per month when the Port Range
   approach is enabled (i.e., use of a Port Range) is around 1,3 Mbytes.
   The one for CG-NAT is around 3,1 Gbytes (Gbytes and not Mbytes) per
   month.

   - Port Range based architecture:

   Amount for 1000 CPEs per month = 1000 (CPEs) * 43 (bytes for the
   tuple with Port Range) * 30 (days in a month) = 1,3 Mbytes

   -CG-NAT:

   {Public IP address - Public Port - Private IP address - Private port
   - protocol - date and hour of the beginning of address/port
   allocation - duration of this allocation (or date and hour of the
   allocation end)}

   = 4 + 2 + + 4 + 2 + 1 + 8 + 8




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   = 29 bytes.

   Note : Storing the customer identification attached to the private
   address is considered negligible in the calculation.

   Amount for 1000 CPEs per month

   = 1000 (CPEs) * 100 (number of new sessions in 10 mn) * 36 (number of
   10 mn durations in 6 h) * 29 (number of bytes per session) * 30 (days
   in a month)

   = 3,1 Gbytes

   Based on this data, a factor of more than 1000 is to be observed
   between the two solutions (in favor of the Port Range approach).

   This factor (i.e., ratio of 1000) is important to be taken into
   account since CAPEX and OPEX would be impacted drastically for the
   implementation of this legal requirement.  Indeed, a large investment
   must be forecast(ed) for deploying a suitable infrastructure (e.g.,
   physical nodes and storage capacity).  Service Providers should
   carefully consider this impact on their legal storage
   infrastructures.

   This factor may be optimized if a port ranges are assigned to
   customers on the CG-NAT device.

   Moreover, as the deployment of the FTTH (Fiber To The Home) will
   progress it is expected that the number of sessions per user will be
   growing which will further increase the amount of data to be stored
   in CG-NAT but not in the Port Range approach.

15.3.  Session Handling in CG-NAT

   The complexity of the real-time processing is related to the number
   of operations to handle the TCP and UDP sessions and associated
   complexity.

   CG-NAT is a NAT and therefore has to monitor dynamically all the
   sessions in order to identify if a public port number is still in-use
   or can be released.  For this purpose, a CG-NAT needs in particular
   to handle timeouts and to scrutinize all TCP session states.  In
   addition the entries enclosed in the NAT table maintained by a given
   CG-NAT is of a much greater complexity than the table in the PRR.
   The CG-NAT needs to keep all the mappings [Public IP address - Public
   Port - protocol - Private IP address - Private Port] for each session
   (UDP or TCP) whilst the PRR has to keep only one entry [Public IP
   address - Port Range - route to the CPE] per CPE.



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   For example, if the CPE handles 100 active sessions, the factor is
   100 between a CG-NAT and a PRR.  For a CPE with 1000 active sessions
   (which may not be so rare for clients making high use of peer to peer
   applications) the factor raises to 1000.  Again, this is not simply a
   matter of factor; with CG-NAT, handling a session is complex as
   already indicated (e.g., timeouts, scrutinizing of session states,
   NAT entries real time maintenance, etc.).

   As for the PRR, it does not handle sessions but simply routes packets
   (routing based on both IP address and Port Range).

   CG-NAT can either be used in a context where the CPE keeps its NAT
   (yielding a double NAT configuration) or in a configuration where the
   CPE is a mere router (or bridge) without any NAT.  In the first case
   (i.e., CPE without NAT) there is only one level of NAT in the path
   (at the CG-NAT level).  All the complexity, today distributed among
   the CPEs, becomes concentrated into CG-NAT equipment.  The cost of
   the CG-NAT is not balanced by a relative simplification of the CPEs
   (no NAT embedded).  In a double NAT configuration the relative
   simplification of the CPE (no NAT embedded) is not even attained.

15.4.  Peer-to-Peer applications

   P2P applications can not work at full capabilities when a CG-NAT is
   in the path.  This is because the peers can not initiate
   communications toward a peer behind a CG-NAT.  Consequently the
   communications must pass through a server which greatly reduces the
   throughput capabilities of the system.  A palliative could be for P2P
   applications to use a STUN server so that they can know the public
   address and port allocated by the CG-NAT and to keep alive the port
   (by periodical short messages).

   There is no such problem with the Port Range approach where the user
   can still as today set manually the port forwarding policies onto his
   CPE (e.g., Through WEB page, provided the choice of the port were
   restricted to the allocated Port Range, etc.).


16.  IANA Considerations

   TBC.


17.  Security Considerations

   This section will be completed in the next version of this draft.





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18.  Contributors

   These authors have contributed to this memo:

   o  Jean-Luc Grimault (France Telecom,
      jeanluc.grimault@orange-ftgroup.com)

   o  Alain Villefranque (France Telecom,
      alain.villefranque@orange-ftgroup.com )


19.  Acknowledgements

   The authors would like to thank Dave THALER and Yoann NOISETTE, for
   their extensive review and technical input, and Mohammed KASSI LAHLOU
   for his suggestion regarding the involvement of the DHCP client
   relay.  We would also like to thank Pierrick MORAND and Mohammed
   ACHEMLAL for their support and suggestions.

   6to4 text has been proposed by D. THALER.


20.  References

20.1.  Normative References

   [RFC1034]  Mockapetris, P., "Domain names - concepts and facilities",
              STD 13, RFC 1034, November 1987.

   [RFC1191]  Mogul, J. and S. Deering, "Path MTU discovery", RFC 1191,
              November 1990.

   [RFC1584]  Moy, J., "Multicast Extensions to OSPF", RFC 1584,
              March 1994.

   [RFC1661]  Simpson, W., "The Point-to-Point Protocol (PPP)", STD 51,
              RFC 1661, July 1994.

   [RFC1858]  Ziemba, G., Reed, D., and P. Traina, "Security
              Considerations for IP Fragment Filtering", RFC 1858,
              October 1995.

   [RFC1889]  Schulzrinne, H., Casner, S., Frederick, R., and V.
              Jacobson, "RTP: A Transport Protocol for Real-Time
              Applications", RFC 1889, January 1996.

   [RFC2026]  Bradner, S., "The Internet Standards Process -- Revision
              3", BCP 9, RFC 2026, October 1996.



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

   [RFC2131]  Droms, R., "Dynamic Host Configuration Protocol",
              RFC 2131, March 1997.

   [RFC3376]  Cain, B., Deering, S., Kouvelas, I., Fenner, B., and A.
              Thyagarajan, "Internet Group Management Protocol, Version
              3", RFC 3376, October 2002.

20.2.  Informative References

   [I-D.bajko-pripaddrassign]
              Bajko, G., Savolainen, T., Boucadair, M., and P. Levis,
              "Port Restricted IP Address Assignment",
              draft-bajko-pripaddrassign-01 (work in progress),
              March 2009.

   [I-D.boucadair-behave-ipv6-portrange]
              Boucadair, M., Levis, P., Grimault, J., Villefranque, A.,
              and M. Kassi-Lahlou, "Flexible IPv6 Migration Scenarios in
              the Context of IPv4 Address Shortage",
              draft-boucadair-behave-ipv6-portrange-01 (work in
              progress), March 2009.

   [I-D.boucadair-pppext-portrange-option]
              Boucadair, M., Levis, P., Grimault, J., and A.
              Villefranque, "Port Range Configuration Options for PPP
              IPCP", draft-boucadair-pppext-portrange-option-00 (work in
              progress), February 2009.

   [I-D.fuller-240space]
              Fuller, V., "Reclassifying 240/4 as usable unicast address
              space", draft-fuller-240space-02 (work in progress),
              March 2008.

   [I-D.ietf-softwire-dual-stack-lite]
              Durand, A., Droms, R., Haberman, B., and J. Woodyatt,
              "Dual-stack lite broadband deployments post IPv4
              exhaustion", draft-ietf-softwire-dual-stack-lite-00 (work
              in progress), March 2009.

   [I-D.savolainen-indicating-240-addresses]
              Savolainen, T., "A way for a host to indicate support for
              240.0.0.0/4 addresses",
              draft-savolainen-indicating-240-addresses-01 (work in
              progress), February 2009.




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   [RFC2236]  Fenner, W., "Internet Group Management Protocol, Version
              2", RFC 2236, November 1997.

   [RFC3056]  Carpenter, B. and K. Moore, "Connection of IPv6 Domains
              via IPv4 Clouds", RFC 3056, February 2001.

   [RFC3261]  Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
              A., Peterson, J., Sparks, R., Handley, M., and E.
              Schooler, "SIP: Session Initiation Protocol", RFC 3261,
              June 2002.

   [RFC3659]  Hethmon, P., "Extensions to FTP", RFC 3659, March 2007.

   [RFC3715]  Aboba, B. and W. Dixon, "IPsec-Network Address Translation
              (NAT) Compatibility Requirements", RFC 3715, March 2004.

   [RFC3947]  Kivinen, T., Swander, B., Huttunen, A., and V. Volpe,
              "Negotiation of NAT-Traversal in the IKE", RFC 3947,
              January 2005.

   [RFC4601]  Fenner, B., Handley, M., Holbrook, H., and I. Kouvelas,
              "Protocol Independent Multicast - Sparse Mode (PIM-SM):
              Protocol Specification (Revised)", RFC 4601, August 2006.


Authors' Addresses

   Mohamed Boucadair (editor)
   France Telecom
   3, Av Francois Chateau
   Rennes  35000
   France

   Email: mohamed.boucadair@orange-ftgroup.com


   Pierre Levis
   France Telecom
   42 rue des Coutures
   BP 6243
   Caen Cedex 4  14066
   France

   Email: pierre.levis@orange-ftgroup.com







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   Gabor Bajko
   Nokia

   Email: gabor.bajko@nokia.com


   Teemu Savolainen
   Nokia
   Hermiankatu 12 D
   FI-33720 TAMPERE
   Finland

   Email: teemu.Savolainen@nokia.com






































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