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Versions: 00 01 02 03 04 05 06 07 08 09 RFC 6431

Network Working Group                                       M. Boucadair
Internet-Draft                                                  P. Levis
Intended status: Experimental                             France Telecom
Expires: March 25, 2011                                         G. Bajko
                                                           T. Savolainen
                                                                   Nokia
                                                      September 21, 2010


             Port Range Configuration Options for PPP IPCP
               draft-boucadair-pppext-portrange-option-04

Abstract

   This document defines two IPCP (IP Configuration Protocol) Options
   used to convey a set of ports.  These options can be used in the
   context of port range-based solutions (port range delegation) or NAT-
   based ones (port delegation or port forwarding).  Architectural
   considerations are out of scope of this document.

Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

Status of this Memo

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

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

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

   This Internet-Draft will expire on March 25, 2011.

Copyright Notice

   Copyright (c) 2010 IETF Trust and the persons identified as the
   document authors.  All rights reserved.




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   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1.  Use Cases  . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Port Range Options . . . . . . . . . . . . . . . . . . . . . .  4
     2.1.  Description of Port Range Value and Port Range Mask  . . .  4
     2.2.  Description of Cryptographically Random Port Range
           option . . . . . . . . . . . . . . . . . . . . . . . . . .  6
     2.3.  Illustration Examples  . . . . . . . . . . . . . . . . . .  8
       2.3.1.  Overview . . . . . . . . . . . . . . . . . . . . . . .  8
       2.3.2.  Successful  Flow: Port Range Options supported by
               both the Client and the Server . . . . . . . . . . . .  8
       2.3.3.  Port Range Option Not Supported by the Server  . . . . 10
       2.3.4.  Port Range Option not Supported by the Client  . . . . 12
   3.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 13
   4.  Security Considerations  . . . . . . . . . . . . . . . . . . . 13
   5.  Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 13
   6.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 13
   7.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 13
     7.1.  Normative References . . . . . . . . . . . . . . . . . . . 13
     7.2.  Informative References . . . . . . . . . . . . . . . . . . 14
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 15

















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1.  Introduction

   Within the context of IPv4 address depletion, several solutions have
   been investigated to share IPv4 addresses.  Two flavours can be
   distinguished: NAT-based solutions (a.k.a., Carrier Grade NAT(CGN,
   [I-D.shirasaki-nat444-isp-shared-addr])) or port range based ones
   ([I-D.boucadair-port-range] and [I-D.ymbk-aplusp] are examples of
   solutions which propose to share the same (public) IP address among
   several devices and to constrain the values used as port sources to a
   limited set of values).  Port range-based solutions do not require an
   additional NAT level in the service provider's domain.  Several means
   may be used to convey Port Range information.

   This document defines the notion of Port Mask which is generic and
   flexible.  Several allocation schemes may be implemented when using a
   Port Mask.  It proposes a basic mechanism that allows the allocation
   of a unique port range to a requesting client.

   This document defines new IPCP options to be used to carry Port Range
   information.  IPCP has been widely used to convey configuration
   information such as IP Compression Protocol [RFC3241][RFC3544] or IP-
   Address [RFC1332].

   IPv4 address exhaustion is only provided as an example of the usage
   of the PPP IPCP Options defined in this document.  In particular,
   Port Range Options may be used independently of the presence of IP-
   Address IPCP Option.

   This document adheres to the consideration defined in [RFC2153].

1.1.  Use Cases

   Port Range Options can be used in port range-based solutions (e.g.,
   [I-D.boucadair-port-range]) or in a CGN-based solution to bypass the
   NAT (i.e., for transparent NAT traversal and avoid involving several
   NAT in the path) or to delegate one or a set of ports to the
   requesting client (e.g., avoid ALG (Application Level Gateway) or for
   port forwarding).

   For improved security an option for delegating cryptographically
   random port range is defined.

1.2.  Terminology

   To differentiate between a Port Range containing a contiguous span of
   port numbers and a Port Range with non contiguous and possibly random
   port numbers, the following denominations are used:




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   o  Contiguous Port Range: a set of port values which form a
      contiguous sequence.

   o  Non Contiguous Port Range: a set of port values which does not
      form a contiguous sequence.

   o  Random Port Range: a cryptographically random set of port values.

   Unless explicitly mentioned, Port Mask refers to the couple (Port
   Range Value, Port Range Mask).

   In addition, this document makes use of the following terms:

   o  Delegated port or port range: a port or a range of ports belonging
      to an IP address managed by an upstream device (such as NAT),
      which are delegated to a client for use as source address and port
      when sending packets.

   o  Forwarded port or port range: a port or a range of ports belonging
      to an IP address managed by an upstream device such as (NAT),
      which is/are statically mapped to the internal IP address of the
      client and same port number of the client.

   This memo uses the same terminology as per [RFC1661].


2.  Port Range Options

   This section defines the IPCP Option for Port Range delegation.

2.1.  Description of Port Range Value and Port Range Mask

   The Port Range Value and Port Range Mask are used to specify one
   range of ports (contiguous or not contiguous) pertaining to a given
   IP address.  Concretely, Port Range Mask and Port Range Value are
   used to notify a remote peer about the Port Mask to be applied when
   selecting a port value as a source port.  The Port Range Value is
   used to infer a set of allowed port values.  A Port Range Mask
   defines a set of ports that all have in common a subset of pre-
   positioned bits.  This set of ports is also called Port Range.  Two
   port numbers are said to belong to the same Port Range if and only
   if, they have the same Port Range Mask.

   A Port Mask is composed of a Port Range Value and a Port Range Mask:

   o  The Port Range Value indicates the value of the significant bits
      of the Port Mask.  The Port Range Value is coded as follows:




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      *  The significant bits may take a value of 0 or 1.

      *  All the other bits (a.k.a., non significant ones) are set to 0.

   o  The Port Range Mask indicates, by the bit(s) set to 1, the
      position of the significant bits of the Port Range Value.

   This IPCP Configuration Option provides a way to negotiate the Port
   Range to be used on the local end of the link.  It allows the sender
   of the Configure-Request message to state which Port Range associated
   with a given IP address is desired, or to request the peer to provide
   the configuration.  The peer can provide this information by NAKing
   the option, and returning a valid Port Range (i.e., (Port Range
   Value, Port Range Mask)).

   When the server assigns only shared IP addresses, the peer MUST
   include Port Range Option in its request.  If not, Protocol-Reject
   sent by the server.

   When a peer issues a request enclosing IPCP Port Range Option, and if
   the server does not support this option, the Port Range Option is
   rejected by the server.

   The Port Range IPCP option adheres to the format defined in Section
   1.1 of [RFC2153].

   The "value" field of the option defined in [RFC2153] when conveying
   Port Range IPCP Option is provided in Figure 1.

       0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |M|          Reserved           |      Port Range Value         |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |      Port Range Mask          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


              Figure 1: Format of the Port Range IPCP Option

   o  M: mode bit.  It indicates the mode the port range is allocated
      for.  A value of zero indicates the port ranges are delegated,
      while a value of 1 indicates the port ranges are port forwarded.

   o  Port Range Value (PRV): PRV indicates the value of the significant
      bits of the Port Mask.  By default, no PRV is assigned.





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   o  Port Range Mask (PRM): Port Range Mask indicates the position of
      the bits which are used to build the Port Range Value.  By
      default, no PRM value is assigned.  The 1 values in the Port Range
      Mask indicate by their position the significant bits of the Port
      Range Value.

   Figure 2 provides an example of the resulting Port Range:

   - Port Range Mask is set to 0001010000000000 (5120) and

   - Port Range Value is set to 0000010000000000 (1024).


       0                   1
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |0 0 0 1 0 1 0 0 0 0 0 0 0 0 0 0|  Port Range Mask
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
             |   |
             |   | (two significant bits)
             v   v
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0|  Port Range Value
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |x x x 0 x 1 x x x x x x x x x x|  Usable ports (x may take a value of 0 or 1).
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


         Figure 2: Example of Port Range Mask and Port Range Value

   Port values belonging to this Port Range must have the 4th bit (resp.
   the sixth one), from the left, set to 0 (resp. 1).  Only these port
   values will be used by the peer when enforcing the configuration
   conveyed by PPP IPCP.

2.2.  Description of Cryptographically Random Port Range option

   A cryptographically random Port Range Option may be used as a
   mitigation tool against blind attacks described in
   [I-D.ietf-tsvwg-port-randomization].

   The benefits of the approach and the method to calculate the
   delegated ports set are described in [I-D.bajko-pripaddrassign].






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   The cryptographically Random Port Range IPCP Option adheres to the
   format defined in Section 1.1 of [RFC2153].  The "value" field of the
   option defined in [RFC2153] when conveying cryptographically Random
   Port Range IPCP Option is illustrated in Figure 3

     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |M|          Reserved           |          function             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |        starting point         |   number of delegated ports   |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                             key K               ...
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     ...                                                           ...
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     ...                                                           ...
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     ...                                                             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


    Figure 3: Format of the cryptographically Random Port Range option

   o  M: mode bit.  It indicates the mode the port range is allocated
      for.  A value of zero indicates the port ranges are delegated,
      while a value of 1 indicates the port ranges are port forwarded.

   o  Function: A 16 bit field whose value is associated with predefined
      encryption functions.  This specification associates value 1 with
      the predefined function described in Section 5 of
      [I-D.bajko-pripaddrassign].

   o  Starting Point: A 16 bit value used as an input to the specified
      function

   o  Number of delegated ports: A 16 bit value specifying the number of
      ports delegated to the client for use as source port values.

   o  Key K: A 128 bit key used as input to the predefined function for
      delegated port calculation.

   When the option is included in the IPCP Configure-Request 'key field'
   and 'starting point' field SHALL be set to all zeros.  The requester
   MAY indicate in the 'function' field which encryption function
   requester prefers, and in the 'number of delegated ports' field the
   number of ports the requester would like to obtain.  If requester has
   no preference it SHALL set also the 'function' field and/or 'number
   of delegated ports' field to zero.



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   The usage of the option in IPCP message negotiation (Request/Reject/
   Nak/Ack) follows the logic described for Port Mask and Port Range
   options at section 2.3.

2.3.  Illustration Examples

2.3.1.  Overview

   These flows provide examples of the usage of IPCP to convey the Port
   Range Option.  As illustrated in Figure 4, IPCP messages are
   exchanged between a Host and a BRAS (Broadband Access Server).

   1.  The first example illustrates a successful IPCP exchange;

   2.  The second example shows the IPCP exchange that occurs when Port
       Range Option is not supported by the server;

   3.  The third example shows the IPCP exchange that occurs when Port
       Range Option is not supported by the client;

   4.  The fourth example shows the IPCP exchange that occurs when Port
       Range Option is not supported by the client and a non null IP
       (i.e., an address different from 0.0.0.0) address is enclosed in
       the first configuration request issued by the peer.

2.3.2.  Successful  Flow: Port Range Options supported by both the
        Client and the Server

   The following message exchange (i.e., Figure 4) provides an example
   of successful IPCP configuration operation when the Port Range IPCP
   Option is used.




















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     +-----+                                          +-----+
     | Host|                                          | BRAS|
     +-----+                                          +-----+
        |                                                |
        |              (1) IPCP Configure-Request        |
        |                IP ADDRESS=0.0.0.0              |
        |                PORT RANGE VALUE=0              |
        |                PORT RANGE MASK=0               |
        |===============================================>|
        |                                                |
        |              (2) IPCP Configure-Nak            |
        |                IP ADDRESS=a.b.c.d              |
        |                PORT RANGE VALUE=80             |
        |                PORT RANGE MASK=496             |
        |<===============================================|
        |                                                |
        |              (3) IPCP Configure-Request        |
        |                IP ADDRESS=a.b.c.d              |
        |                PORT RANGE VALUE=80             |
        |                PORT RANGE MASK=496             |
        |===============================================>|
        |                                                |
        |              (4) IPCP Configure-Ack            |
        |                IP ADDRESS=a.b.c.d              |
        |                PORT RANGE VALUE=80             |
        |                PORT RANGE MASK=496             |
        |<===============================================|
        |                                                |


                        Figure 4: Successful  flow

   The main steps of this flow are listed below:

      (1) The Host sends a first Configure-Request which includes the
      set of options it desires to negotiate.  All these Configuration
      Options are negotiated simultaneously.  In this example,
      Configure-Request carries information about IP-address, Port Range
      Value and Port Range Mask.  In this example, IP-address Option is
      set to 0.0.0.0, Port Range Value is set to 0 and Port Range Mask
      is set to 0.

      (2) BRAS sends back a Configure-Nak and sets the enclosed options
      to its preferred values.  In this example: IP-Address Option is
      set to a.b.c.d, Port Range Value is set to 80 and Port Range Mask
      is set to 496.





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      (3) The Host re-sends a Configure-Request requesting IP-address
      Option to be set to a.b.c.d, Port Range Value to be set to 80 and
      Port Range Mask to be set to 496.

      (4) BRAS sends a Configure-Ack message

   As a result of this exchange, Host is configured to use as local IP
   address a.b.c.d and the following 128 contiguous Port Ranges
   resulting of the Port Mask (Port Range Value == 0, Port Range Mask ==
   496):

      - from 80 to 95

      - from 592 to 607

      - ...

      - from 65104 to 65119

2.3.3.  Port Range Option Not Supported by the Server

   This example (Figure 5) depicts an exchange of messages when the BRAS
   does not support IPCP Port Range Option.




























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     +-----+                                          +-----+
     | Host|                                          | BRAS|
     +-----+                                          +-----+
        |                                                |
        |              (1) IPCP Configure-Request        |
        |                IP ADDRESS=0.0.0.0              |
        |                PORT RANGE VALUE=0              |
        |                PORT RANGE MASK=0               |
        |===============================================>|
        |                                                |
        |              (2) IPCP Configure-Reject         |
        |                PORT RANGE VALUE=0              |
        |                PORT RANGE MASK=0               |
        |<===============================================|
        |                                                |
        |              (3) IPCP Configure-Request        |
        |                IP ADDRESS=0.0.0.0              |
        |===============================================>|
        |                                                |
        |              (4) IPCP Configure-Nak            |
        |                IP ADDRESS=a.b.c.d              |
        |<===============================================|
        |                                                |
        |              (5) IPCP Configure-Request        |
        |                IP ADDRESS=a.b.c.d              |
        |===============================================>|
        |                                                |
        |              (6) IPCP Configure-Ack            |
        |                IP ADDRESS=a.b.c.d              |
        |<===============================================|
        |                                                |


   Figure 5: Failed  flow: Port Range Option not supported by the server

   The main steps of this flow are listed hereafter:

      (1) The Host sends a first Configure-Request which includes the
      set of options it desires to negotiate.  All these Configuration
      Options are negotiated simultaneously.  In this example,
      Configure-Request carries the codes of IP-address, Port Range
      Value and Port Range Mask options.  In this example, IP-address
      Option is set to 0.0.0.0, Port Range Value is set to 0 and Port
      Range Mask is set to 0.

      (2) BRAS sends back a Configure-Reject to decline Port Range
      option.




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      (3) The Host sends a Configure-Request which includes only the
      codes of IP-Address option.  In this example, IP-Address Option is
      set to 0.0.0.0.

      (4) BRAS sends back a Configure-Nak and sets the enclosed option
      to its preferred value.  In this example: IP-Address Option is set
      to a.b.c.d.

      (5) The Host re-sends a Configure-Request requesting IP-Address
      Option to be set to a.b.c.d.

      (6) BRAS sends a Configure-Ack message.

   As a result of this exchange, Host is configured to use as local IP
   address a.b.c.d.  This IP address is not a shared IP address.

2.3.4.  Port Range Option not Supported by the Client

   This example (Figure 6) depicts exchanges when only shared IP
   addresses are assigned to end-user's devices.  The server is
   configured to assign only shared IP addresses.  If Port Range Options
   are not enclosed in the configuration request, the request is
   rejected and the requesting peer will be unable to access the service
   as depicted in Figure 6.


     +-----+                                          +-----+
     | Host|                                          | BRAS|
     +-----+                                          +-----+
        |                                                |
        |              (1) IPCP Configure-Request        |
        |                IP ADDRESS=0.0.0.0              |
        |===============================================>|
        |                                                |
        |              (2) IPCP Protocol-Reject          |
        |<===============================================|
        |                                                |


          Figure 6: Port Range Option not supported by the Client

   The main steps of this flow are:

      (1) The Host sends a Configure-Request requesting IP-Address
      Option to be set to 0.0.0.0 and without enclosing the Port Range
      Option.





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      (2) BRAS sends a Protocol-Reject message.

   As a result of this exchange, Host is not able to access the service.


3.  IANA Considerations

   No action is required from IANA since this document adheres to
   [RFC2153].


4.  Security Considerations

   This document does not introduce any security issue in addition to
   those related to PPP.  Service providers should use authentication
   mechanisms such as CHAP [RFC1994] or PPP link encryption [RFC1968].

   Use of small and non-random port range may increase host exposure to
   attacks described [I-D.ietf-tsvwg-port-randomization].  This risk can
   be mitigated by using larger range or by using Random Port Range
   Option.


5.  Contributors

   Jean-Luc Grimault and Alain Villefranque contributed to this
   document.


6.  Acknowledgements

   The authors would like to thank Christian Jacquenet and James Carlson
   for their review.


7.  References

7.1.  Normative References

   [RFC1332]  McGregor, G., "The PPP Internet Protocol Control Protocol
              (IPCP)", RFC 1332, May 1992.

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

   [RFC1968]  Meyer, G. and K. Fox, "The PPP Encryption Control Protocol
              (ECP)", RFC 1968, June 1996.




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   [RFC1994]  Simpson, W., "PPP Challenge Handshake Authentication
              Protocol (CHAP)", RFC 1994, August 1996.

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

   [RFC2153]  Simpson, W. and K. Fox, "PPP Vendor Extensions", RFC 2153,
              May 1997.

7.2.  Informative References

   [I-D.bajko-pripaddrassign]
              Bajko, G., Savolainen, T., Boucadair, M., and P. Levis,
              "Port Restricted IP Address Assignment",
              draft-bajko-pripaddrassign-02 (work in progress),
              October 2009.

   [I-D.boucadair-port-range]
              Boucadair, M., Levis, P., Bajko, G., and T. Savolainen,
              "IPv4 Connectivity Access in the Context of IPv4 Address
              Exhaustion: Port Range based IP Architecture",
              draft-boucadair-port-range-02 (work in progress),
              July 2009.

   [I-D.ietf-tsvwg-port-randomization]
              Larsen, M. and F. Gont, "Transport Protocol Port
              Randomization Recommendations",
              draft-ietf-tsvwg-port-randomization-09 (work in progress),
              August 2010.

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

   [I-D.ymbk-aplusp]
              Bush, R., "The A+P Approach to the IPv4 Address Shortage",
              draft-ymbk-aplusp-05 (work in progress), October 2009.

   [RFC3241]  Bormann, C., "Robust Header Compression (ROHC) over PPP",
              RFC 3241, April 2002.

   [RFC3544]  Koren, T., Casner, S., and C. Bormann, "IP Header
              Compression over PPP", RFC 3544, July 2003.






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Authors' Addresses

   Mohamed Boucadair
   France Telecom
   3, Av Francois Chateau
   Rennes  35000
   France

   Email: mohamed.boucadair@orange-ftgroup.com


   Pierre Levis
   France Telecom

   Email: pierre.levis@orange-ftgroup.com


   Gabor Bajko
   Nokia

   Email: gabor(dot)bajko(at)nokia(dot)com


   Teemu Savolainen
   Nokia

   Email: teemu.savolainen@nokia.com
























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