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rfc:rfc6431

Independent Submission M. Boucadair Request for Comments: 6431 P. Levis Category: Informational France Telecom ISSN: 2070-1721 G. Bajko

                                                         T. Savolainen
                                                                 Nokia
                                                               T. Tsou
                                             Huawei Technologies (USA)
                                                         November 2011
          Huawei Port Range Configuration Options for PPP
                     IP Control Protocol (IPCP)

Abstract

 This document defines two Huawei IPCP (IP Control Protocol) options
 used to convey a set of ports.  These options can be used in the
 context of port range-based solutions or NAT-based solutions for port
 delegation and forwarding purposes.

Status of This Memo

 This document is not an Internet Standards Track specification; it is
 published for informational purposes.
 This is a contribution to the RFC Series, independently of any other
 RFC stream.  The RFC Editor has chosen to publish this document at
 its discretion and makes no statement about its value for
 implementation or deployment.  Documents approved for publication by
 the RFC Editor are not a candidate for any level of Internet
 Standard; see Section 2 of RFC 5741.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 http://www.rfc-editor.org/info/rfc6431.

Copyright Notice

 Copyright (c) 2011 IETF Trust and the persons identified as the
 document authors.  All rights reserved.
 This document is subject to BCP 78 and the IETF Trust's Legal
 Provisions Relating to IETF Documents
 (http://trustee.ietf.org/license-info) in effect on the date of
 publication of this document.  Please review these documents
 carefully, as they describe your rights and restrictions with respect
 to this document.

Boucadair, et al. Informational [Page 1] RFC 6431 Port Range IPCP Options November 2011

Table of Contents

 1. Introduction ....................................................2
    1.1. Use Cases ..................................................3
    1.2. Terminology ................................................3
    1.3. Requirements Language ......................................4
 2. Port Range Options ..............................................4
    2.1. Description of Port Range Value and Port Range Mask ........4
    2.2. Cryptographically Random Port Range Option .................6
         2.2.1. Random Port Delegation Function .....................6
         2.2.2. Description of Cryptographically Random Port
                Range Option ........................................8
    2.3. Illustration Examples .....................................10
         2.3.1. Overview ...........................................10
         2.3.2. Successful Flow: Port Range Options Supported
                by Both the Client and the Server ..................10
         2.3.3. Port Range Option Not Supported by the Server ......11
         2.3.4. Port Range Option Not Supported by the Client ......13
 3. Security Considerations ........................................14
 4. Contributors ...................................................14
 5. Acknowledgements ...............................................14
 6. References .....................................................14
    6.1. Normative References ......................................14
    6.2. Informative References ....................................15

1. Introduction

 Within the context of IPv4 address depletion, several solutions have
 been investigated to share IPv4 addresses.  Two flavors can be
 distinguished: NAT-based solutions (e.g., Carrier-Grade NAT (CGN)
 [CGN-REQS]) and port range-based solutions (e.g., [RFC6346]
 [PORT-RANGE-ARCH] [SAM]).  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
 Huawei IPCP options to be used to carry port range information.
 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 the
 IP-Address IPCP Option.
 This document adheres to the considerations defined in [RFC2153].

Boucadair, et al. Informational [Page 2] RFC 6431 Port Range IPCP Options November 2011

 This document is not a product of the PPPEXT working group.
 Note that IPR disclosures apply to this document (see
 https://datatracker.ietf.org/ipr/).

1.1. Use Cases

 Port Range options can be used in port range-based solutions (e.g.,
 [RFC6346]) or in a CGN-based solution.  These options can be used in
 a CGN context to bypass the NAT (i.e., for transparent NAT traversal,
 and to avoid involving several NAT levels in the path) or to delegate
 one or a set of ports to the requesting client (e.g., to avoid the
 ALG (Application Level Gateway), or for port forwarding).
 Section 3.3.1 of [RFC6346] specifies an example of usage of the
 options defined in this document.

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:
 o  Contiguous Port Range: A set of port values that form a contiguous
    sequence.
 o  Non-Contiguous Port Range: A set of port values that do not form a
    contiguous sequence.
 o  Random Port Range: A cryptographically random set of port values.
 Unless explicitly mentioned, "Port Mask" refers to the tuple (Port
 Range Value, Port Range Mask).
 In addition, this document makes use of the following terms:
 o  Delegated port or delegated port range: A port or a range of ports
    that belong to an IP address managed by an upstream device (such
    as NAT) and that are delegated to a client for use as the source
    address and port when sending packets.
 o  Forwarded port or forwarder port range: A port or a range of ports
    that belong to an IP address managed by an upstream device such as
    (NAT) and that 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 [RFC1661].

Boucadair, et al. Informational [Page 3] RFC 6431 Port Range IPCP Options November 2011

1.3. 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].

2. Port Range Options

 This section defines the IPCP Option for port range delegation.  The
 format of vendor-specific options is defined in [RFC2153].  Below are
 the values to be conveyed when the Port Range Option is used:
 o  Organizationally Unique Identifier (OUI): This field is set to
    781DBA (hex).
 o  Kind: This field is set to F0 (hex).
 o  Value(s): The content of this field is specified in Sections 2.1
    and 2.2.2.

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 non-contiguous) pertaining to a given
 IP address.  Concretely, the 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 referred to as the
 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:
  • The significant bits may take a value of 0 or 1.
  • All of the other bits (i.e., 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.

Boucadair, et al. Informational [Page 4] RFC 6431 Port Range IPCP Options November 2011

 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 that the peer
 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)).
 If a peer issues a request enclosing the IPCP Port Range Option and
 the server does not support this option, the Port Range Option is
 rejected by the server.
 The set of ports conveyed in an IPCP Port Range Option applies to all
 transport protocols.
 The set of ports conveyed in an IPCP Port Range Option is revoked
 when the link is no longer up (e.g., when Terminate-Request and
 Terminate-Ack are exchanged).
 The Port Range IPCP option adheres to the format defined in
 Section 2.1 of [RFC2153].  The "Value(s)" field of the option defined
 in [RFC2153] when conveying the 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          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Most significant bit (MSB) network order is used for encoding the
 Port Range Value and Port Range Mask fields.
            Figure 1: Format of the Port Range IPCP Option
 o  M: mode bit.  The mode bit indicates the mode for which the port
    range is allocated.  A value of zero indicates that the port
    ranges are delegated, while a value of 1 indicates that the port
    ranges are port-forwarded.
 o  Port Range Value (PRV): The PRV indicates the value of the
    significant bits of the Port Mask.  By default, no PRV is
    assigned.

Boucadair, et al. Informational [Page 5] RFC 6431 Port Range IPCP Options November 2011

 o  Port Range Mask (PRM): The Port Range Mask indicates the position
    of the bits that 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:
  1. The Port Range Mask is set to 0001010000000000 (5120).
  1. The 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 be set to 0 or 1)
       Figure 2: Example of Port Range Mask and Port Range Value
 Port values belonging to this port range must have the fourth bit
 from the left set to 0, and the sixth bit from the left set to 1.
 Only these port values will be used by the peer when enforcing the
 configuration conveyed by PPP IPCP.

2.2. Cryptographically Random Port Range Option

 A cryptographically random Port Range Option may be used as a
 mitigation tool against blind attacks such as those described in
 [RFC6056].

2.2.1. Random Port Delegation Function

 Delegating random ports can be achieved by defining a function that
 takes as input a key 'K' and an integer 'x' within the 1024-65535
 port range and produces an output 'y' also within the 1024-65535 port
 range.

Boucadair, et al. Informational [Page 6] RFC 6431 Port Range IPCP Options November 2011

 The cryptographic mechanism uses the 1024-65535 port range rather
 than the ephemeral range, 49152-65535, for generating a set of ports
 to optimize IPv4 address utilization efficiency (see "Appendix B.
 Address Space Multiplicative Factor" of [RFC6269]).  This behavior is
 compliant with the recommendation to use the whole 1024-65535 port
 range for the ephemeral port selection algorithms (see Section 3.2 of
 [RFC6056]).
 The cryptographic mechanism ensures that the entire 64k port range
 can be efficiently distributed to multiple nodes such that when nodes
 calculate the ports, the results will never overlap with ports that
 other nodes have calculated (property of permutation), and ports in
 the reserved range (smaller than 1024) are not used.  As the
 randomization is done cryptographically, an attacker seeing a node
 using some port X cannot determine which other ports the node may be
 using (as the attacker does not know the key).  Calculation of the
 random port list is done as follows:
 The cryptographic mechanism uses an encryption function y = E(K,x)
 that takes as input a key K (for example, 128 bits) and an integer x
 (the plaintext) in the 1024-65535 port range, and produces an output
 y (the ciphertext), also an integer in the 1024-65535 port range.
 This section describes one such encryption function, but others are
 also possible.
 The server will select the key K.  When the server wants to allocate,
 for example, 2048 random ports, it selects a starting point 'a'
 (1024 <= a <= 65536-2048) such that the port range (a, a+2048) does
 not overlap with any other active client, and calculates the values
 E(K,a), E(K,a+1), E(K,a+2), ..., E(K,a+2046), E(K,a+2047).  These are
 the port numbers allocated for this node.  Instead of sending the
 port numbers individually, the server just sends the values 'K', 'a',
 and '2048'.  The client will then repeat the same calculation.
 The server SHOULD use a different key K for each IPv4 address it
 allocates, to make attacks as difficult as possible.  This way,
 learning the key K used in IPv4 address IP1 would not help in
 attacking IPv4 address IP2 where IP2 is allocated by the same server
 to different nodes.
 With typical encryption functions (such as AES and DES), the input
 (plaintext) and output (ciphertext) are blocks of some fixed size --
 for example, 128 bits for AES, and 64 bits for DES.  For port
 randomization, we need an encryption function whose input and output
 is an integer in the 1024-65535 port range.

Boucadair, et al. Informational [Page 7] RFC 6431 Port Range IPCP Options November 2011

 One possible way to do this is to use the 'Generalized Feistel
 Cipher' [CIPHERS] construction by Black and Rogaway, with AES as the
 underlying round function.
 This would look as follows (using pseudo-code):
         def E(k, x):
             y = Feistel16(k, x)
             if y >= 1024:
                   return y
             else:
                   return E(k, y)
 Note that although E(k,x) is recursive, it is guaranteed to
 terminate.  The average number of iterations is just slightly over 1.
 Feistel16 is a 16-bit block cipher:
         def Feistel16(k, x):
             left = x & 0xff
             right = x >> 8
             for round = 1 to 3:
                 temp = left ^ FeistelRound(k, round, right))
                 left = right
                 right = temp
             return (right << 8) | left
 The Feistel round function uses:
         def FeistelRound(k, round, x):
             msg[0] = round
             msg[1] = x
             msg[2...15] = 0
             return AES(k, msg)[0]
 Performance: To generate a list of 2048 port numbers, about 6000
 calls to AES are required (i.e., encrypting 96 kilobytes).  Thus, it
 will not be a problem for any device that can do, for example, HTTPS
 (web browsing over Secure Sockets Layer/Transport Layer Security
 (SSL/TLS)).

2.2.2. Description of Cryptographically Random Port Range Option

 The cryptographically random Port Range IPCP Option adheres to the
 format defined in Section 2.1 of [RFC2153].  The "Value(s)" field of
 the option defined in [RFC2153] when conveying the cryptographically
 random Port Range IPCP Option is illustrated in Figure 3.

Boucadair, et al. Informational [Page 8] RFC 6431 Port Range IPCP Options November 2011

   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.  The mode bit indicates the mode for which the port
    range is allocated.  A value of zero indicates that the port
    ranges are delegated, while a value of 1 indicates that 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 2.2.1.
 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, the "Key
 K" and "Starting Point" fields SHALL be set to all zeros.  The
 requester MAY indicate in the "Function" field which encryption
 function the requester prefers, and in the "Number of Delegated
 Ports" field the number of ports the requester would like to obtain.
 If the requester has no preference, it SHALL also set the "Function"
 field and/or "Number of Delegated Ports" field to zero.
 The usage of the option in IPCP message negotiation (Request/Reject/
 Nak/Ack) follows the logic described for Port Mask and Port Range
 options in Section 2.1.

Boucadair, et al. Informational [Page 9] RFC 6431 Port Range IPCP Options November 2011

2.3. Illustration Examples

2.3.1. Overview

 The following flows provide examples of the usage of IPCP to convey
 the Port Range Option.  As illustrated in Figures 4, 5, and 6, IPCP
 messages are exchanged between a Host and a BRAS (Broadband Remote
 Access Server).

2.3.2. Successful Flow: Port Range Options Supported by Both the Client

      and the Server
 The following message exchange (Figure 4) depicts a successful IPCP
 configuration operation where the Port Range IPCP Option is used.
   +-----+                                          +-----+
   | 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

Boucadair, et al. Informational [Page 10] RFC 6431 Port Range IPCP Options November 2011

 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 of these
         configuration options are negotiated simultaneously.  In this
         step, the Configure-Request carries information about the IP
         address, the Port Range Value, and the Port Range Mask.  The
         IP-Address Option is set to 0.0.0.0, the Port Range Value is
         set to 0, and the Port Range Mask is set to 0.
    (2)  The BRAS sends back a Configure-Nak and sets the enclosed
         options to its preferred values.  In this step, the
         IP-Address Option is set to a.b.c.d, the Port Range Value is
         set to 80, and the Port Range Mask is set to 496.
    (3)  The Host re-sends a Configure-Request requesting that the
         IP-Address Option be set to a.b.c.d, the Port Range Value be
         set to 80, and the Port Range Mask be set to 496.
    (4)  The BRAS sends a Configure-Ack message.
 As a result of this exchange, the Host is configured to use a.b.c.d
 as its local IP address, and the following 128 contiguous port ranges
 resulting from the Port Mask (Port Range Value == 0, Port Range Mask
 == 496):
  1. from 80 to 95
  1. from 592 to 607
  1. from 65104 to 65119

2.3.3. Port Range Option Not Supported by the Server

 Figure 5 depicts an exchange of messages where the BRAS does not
 support the IPCP Port Range Option.

Boucadair, et al. Informational [Page 11] RFC 6431 Port Range IPCP Options November 2011

   +-----+                                          +-----+
   | 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 below:
    (1)  The Host sends a first Configure-Request, which includes the
         set of options it desires to negotiate.  All of these
         configuration options are negotiated simultaneously.  In this
         step, the Configure-Request carries the codes of the
         IP-Address, Port Range Value, and Port Range Mask options.
         The IP-Address Option is set to 0.0.0.0, the Port Range Value
         is set to 0, and the Port Range Mask is set to 0.
    (2)  The BRAS sends back a Configure-Reject to decline the Port
         Range Option.

Boucadair, et al. Informational [Page 12] RFC 6431 Port Range IPCP Options November 2011

    (3)  The Host sends a Configure-Request, which includes only the
         codes of the IP-Address Option.  In this step, the IP-Address
         Option is set to 0.0.0.0.
    (4)  The BRAS sends back a Configure-Nak and sets the enclosed
         option to its preferred value.  In this step, the IP-Address
         Option is set to a.b.c.d.
    (5)  The Host re-sends a Configure-Request requesting that the
         IP-Address Option be set to a.b.c.d.
    (6)  The BRAS sends a Configure-Ack message.
 As a result of this exchange, the Host is configured to use a.b.c.d
 as its local IP address.  This IP address is not a shared IP address.

2.3.4. Port Range Option Not Supported by the Client

 Figure 6 depicts exchanges where only shared IP addresses are
 assigned to end-users' 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.
   +-----+                                          +-----+
   | 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 listed below:
    (1)  The Host sends a Configure-Request requesting that the
         IP-Address Option be set to 0.0.0.0, and without enclosing
         the Port Range Option.
    (2)  The BRAS sends a Protocol-Reject message.
 As a result of this exchange, the Host is not able to access the
 service.

Boucadair, et al. Informational [Page 13] RFC 6431 Port Range IPCP Options November 2011

3. Security Considerations

 This document does not introduce any security issues in addition to
 those related to PPP.  Service providers should use authentication
 mechanisms such as the Challenge Handshake Authentication Protocol
 (CHAP) [RFC1994] or PPP link encryption [RFC1968].
 The use of small and non-random port ranges may increase host
 exposure to attacks, as described in [RFC6056].  This risk can be
 reduced by using larger port ranges, by using the random Port Range
 Option, or by activating means to improve the robustness of TCP
 against blind in-window attacks [RFC5961].

4. Contributors

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

5. Acknowledgements

 The authors would like to thank C. Jacquenet, J. Carlson, B.
 Carpenter, M. Townsley, and J. Arkko for their review.

6. References

6.1. Normative References

 [RFC1661]  Simpson, W., Ed., "The Point-to-Point Protocol (PPP)",
            STD 51, RFC 1661, July 1994.
 [RFC1968]  Meyer, G., "The PPP Encryption Control Protocol (ECP)",
            RFC 1968, June 1996.
 [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., "PPP Vendor Extensions", RFC 2153, May 1997.
 [RFC5961]  Ramaiah, A., Stewart, R., and M. Dalal, "Improving TCP's
            Robustness to Blind In-Window Attacks", RFC 5961,
            August 2010.

Boucadair, et al. Informational [Page 14] RFC 6431 Port Range IPCP Options November 2011

6.2. Informative References

 [CGN-REQS]
            Perreault, S., Ed., Yamagata, I., Miyakawa, S., Nakagawa,
            A., and H. Ashida, "Common requirements for Carrier Grade
            NAT (CGN)", Work in Progress, October 2011.
 [CIPHERS]  Black, J. and P. Rogaway, "Ciphers with Arbitrary Finite
            Domains.  Topics in Cryptology", CT-RSA 2002, Lecture
            Notes in Computer Science, vol. 2271, 2002.
 [PORT-RANGE-ARCH]
            Boucadair, M., Ed., Levis, P., Bajko, G., and T.
            Savolainen, "IPv4 Connectivity Access in the Context of
            IPv4 Address Exhaustion: Port Range based IP
            Architecture", Work in Progress, July 2009.
 [RFC6056]  Larsen, M. and F. Gont, "Recommendations for Transport-
            Protocol Port Randomization", BCP 156, RFC 6056,
            January 2011.
 [RFC6269]  Ford, M., Ed., Boucadair, M., Durand, A., Levis, P., and
            P. Roberts, "Issues with IP Address Sharing", RFC 6269,
            June 2011.
 [RFC6346]  Bush, R., Ed., "The Address plus Port (A+P) Approach to
            the IPv4 Address Shortage", RFC 6346, August 2011.
 [SAM]      Despres, R., "Scalable Multihoming across IPv6 Local-
            Address Routing Zones Global-Prefix/Local-Address
            Stateless Address Mapping (SAM)", Work in Progress,
            July 2009.

Boucadair, et al. Informational [Page 15] RFC 6431 Port Range IPCP Options November 2011

Authors' Addresses

 Mohamed Boucadair
 France Telecom
 Rennes  35000
 France
 EMail: mohamed.boucadair@orange.com
 Pierre Levis
 France Telecom
 Caen
 France
 EMail: pierre.levis@orange.com
 Gabor Bajko
 Nokia
 EMail: gabor.bajko@nokia.com
 Teemu Savolainen
 Nokia
 EMail: teemu.savolainen@nokia.com
 Tina Tsou
 Huawei Technologies (USA)
 2330 Central Expressway
 Santa Clara, CA  95050
 USA
 Phone: +1 408 330 4424
 EMail: tina.tsou.zouting@huawei.com

Boucadair, et al. Informational [Page 16]

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