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rfc:rfc6888

Internet Engineering Task Force (IETF) S. Perreault, Ed. Request for Comments: 6888 Viagenie BCP: 127 I. Yamagata Updates: 4787 S. Miyakawa Category: Best Current Practice NTT Communications ISSN: 2070-1721 A. Nakagawa

                                        Japan Internet Exchange (JPIX)
                                                             H. Ashida
                                                         Cisco Systems
                                                            April 2013
         Common Requirements for Carrier-Grade NATs (CGNs)

Abstract

 This document defines common requirements for Carrier-Grade NATs
 (CGNs).  It updates RFC 4787.

Status of This Memo

 This memo documents an Internet Best Current Practice.
 This document is a product of the Internet Engineering Task Force
 (IETF).  It represents the consensus of the IETF community.  It has
 received public review and has been approved for publication by the
 Internet Engineering Steering Group (IESG).  Further information on
 BCPs is available in Section 2 of RFC 5741.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 http://www.rfc-editor.org/info/rfc6888.

Copyright Notice

 Copyright (c) 2013 IETF Trust and the persons identified as the
 document authors.  All rights reserved.
 This document is subject to BCP 78 and the IETF Trust's Legal
 Provisions Relating to IETF Documents
 (http://trustee.ietf.org/license-info) in effect on the date of
 publication of this document.  Please review these documents
 carefully, as they describe your rights and restrictions with respect
 to this document.  Code Components extracted from this document must
 include Simplified BSD License text as described in Section 4.e of
 the Trust Legal Provisions and are provided without warranty as
 described in the Simplified BSD License.

Perreault, et al. Best Current Practice [Page 1] RFC 6888 CGN Requirements April 2013

Table of Contents

 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . .  2
 2. Terminology  . . . . . . . . . . . . . . . . . . . . . . . .  3
 3. Requirements for CGNs  . . . . . . . . . . . . . . . . . . .  4
 4. Logging  . . . . . . . . . . . . . . . . . . . . . . . . . . 10
 5. Port Allocation Scheme . . . . . . . . . . . . . . . . . . . 11
 6. Deployment Considerations  . . . . . . . . . . . . . . . . . 11
 7. Security Considerations  . . . . . . . . . . . . . . . . . . 12
 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 12
 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 12
    9.1. Normative References  . . . . . . . . . . . . . . . . . 12
    9.2. Informative Reference . . . . . . . . . . . . . . . . . 13

1. Introduction

 With the shortage of IPv4 addresses, it is expected that more
 Internet Service Providers (ISPs) may want to provide a service where
 a public IPv4 address would be shared by many subscribers.  Each
 subscriber is assigned a private address, and a Network Address
 Translator (NAT) [RFC2663] situated in the ISP's network translates
 the traffic between private and public addresses.  When a second IPv4
 NAT is located at the customer edge, this results in two layers of
 NAT.
 This service can conceivably be offered alongside others, such as
 IPv6 services or regular IPv4 service assigning public addresses to
 subscribers.  Some ISPs started offering such a service long before
 there was a shortage of IPv4 addresses, showing that there are
 driving forces other than the shortage of IPv4 addresses.  One
 approach to CGN deployment is described in [RFC6264].
 This document describes behavior that is required of those multi-
 subscriber NATs for interoperability.  It is not an IETF endorsement
 of CGNs or a real specification for CGNs; rather, it is just a
 minimal set of requirements that will increase the likelihood of
 applications working across CGNs.
 Because subscribers do not receive unique IPv4 addresses, Carrier-
 Grade NATs introduce substantial limitations in communications
 between subscribers and with the rest of the Internet.  In
 particular, it is considerably more involved to establish proxy
 functionality at the border between internal and external realms.
 Some applications may require substantial enhancements, while some
 others may not function at all in such an environment.  Please see
 "Issues with IP Address Sharing" [RFC6269] for details.

Perreault, et al. Best Current Practice [Page 2] RFC 6888 CGN Requirements April 2013

 This document builds upon previous works describing requirements for
 generic NATs [RFC4787][RFC5382][RFC5508].  These documents, and their
 updates if any, still apply in this context.  What follows are
 additional requirements, to be satisfied on top of previous ones.

2. Terminology

 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 [RFC2119].
 Readers are expected to be familiar with "Network Address Translation
 (NAT) Behavioral Requirements for Unicast UDP" [RFC4787] and the
 terms defined there.  The following additional term is used in this
 document:
 Carrier-Grade NAT (CGN):  A NAT-based [RFC2663] logical function used
    to share the same IPv4 address among several subscribers.  A CGN
    is not managed by the subscribers.
       Note that the term "carrier-grade" has nothing to do with the
       quality of the NAT; that is left to discretion of implementers.
       Rather, it is to be understood as a topological qualifier: the
       NAT is placed in an ISP's network and translates the traffic of
       potentially many subscribers.  Subscribers have limited or no
       control over the CGN, whereas they typically have full control
       over a NAT placed on their premises.
       Note also that the CGN described in this document is IPv4-only.
       IPv6 address translation is not considered.
       However, the scenario in which the IPv4-only CGN logical
       function is used may include IPv6 elements.  For example, Dual-
       Stack Lite (DS-Lite) [RFC6333] uses an IPv4-only CGN logical
       function in a scenario making use of IPv6 encapsulation.
       Therefore, this document would also apply to the CGN part of
       DS-Lite.

Perreault, et al. Best Current Practice [Page 3] RFC 6888 CGN Requirements April 2013

 Figure 1 summarizes a common network topology in which a CGN
 operates.
                                 .
                                 :
                                 |       Internet
                 ............... | ...................
                                 |       ISP network
                 External pool:  |
                 192.0.2.1/26    |
                             ++------++  External realm
                 ........... |  CGN   |...............
                             ++------++  Internal realm
                      10.0.0.1 |    |
                               |    |
                               |    |    ISP network
                 ............. | .. | ................
                               |    |  Customer premises
                    10.0.0.100 |    | 10.0.0.101
                       ++------++  ++------++
                       |  CPE1  |  |  CPE2  |  etc.
                       ++------++  ++------++
             (IP addresses are only for example purposes)
                    Figure 1: CGN Network Topology
 Another possible topology is one for hotspots, where there is no
 customer premise or customer premises equipment (CPE), but where a
 CGN serves a bunch of customers who don't trust each other; hence,
 fairness is an issue.  One important difference with the previous
 topology is the absence of a second layer of NAT.  This, however, has
 no impact on CGN requirements since they are driven by fairness and
 robustness in the service provided to customers, which applies in
 both cases.

3. Requirements for CGNs

 What follows is a list of requirements for CGNs.  They are in
 addition to those found in other documents such as [RFC4787],
 [RFC5382], and [RFC5508].
 REQ-1:  If a CGN forwards packets containing a given transport
    protocol, then it MUST fulfill that transport protocol's
    behavioral requirements.  Current applicable documents are as
    follows:
    a.  "NAT Behavioral Requirements for Unicast UDP" [RFC4787]

Perreault, et al. Best Current Practice [Page 4] RFC 6888 CGN Requirements April 2013

    b.  "Network Address Translation (NAT) Behavioral Requirements for
        TCP" [RFC5382]
    c.  "NAT Behavioral Requirements for ICMP" [RFC5508]
    d.  "Network Address Translation (NAT) Behavioral Requirements for
        the Datagram Congestion Control Protocol (DCCP)" [RFC5597]
    Any future NAT behavioral requirements documents for IPv4
    transport protocols will impose additional requirements for CGNs
    on top of those stated here.
 Justification:  It is crucial for CGNs to maximize the set of
    applications that can function properly across them.  The IETF has
    documented the best current practices for UDP, TCP, ICMP, and
    DCCP.
 REQ-2:  A CGN MUST have a default "IP address pooling" behavior of
    "Paired" (as defined in Section 4.1 of [RFC4787]).  A CGN MAY
    provide a mechanism for administrators to change this behavior on
    an application protocol basis.
  • When multiple overlapping internal IP address ranges share the

same external IP address pool (e.g., DS-Lite [RFC6333]), the

       "IP address pooling" behavior applies to mappings between
       external IP addresses and internal subscribers rather than
       between external and internal IP addresses.
 Justification:  This stronger form of REQ-2 from [RFC4787] is
    justified by the stronger need for not breaking applications that
    depend on the external address remaining constant.
    Note that this requirement applies regardless of the transport
    protocol.  In other words, a CGN must use the same external IP
    address mapping for all sessions associated with the same internal
    IP address, be they TCP, UDP, ICMP, something else, or a mix of
    different protocols.
    The justification for allowing other behaviors is to allow the
    administrator to save external addresses and ports for application
    protocols that are known to work fine with other behaviors in
    practice.  However, the default behavior MUST be "Paired".
 REQ-3:  The CGN function SHOULD NOT have any limitations on the size
    or the contiguity of the external address pool.  In particular,
    the CGN function MUST be configurable with contiguous or non-
    contiguous external IPv4 address ranges.

Perreault, et al. Best Current Practice [Page 5] RFC 6888 CGN Requirements April 2013

 Justification:  Given the increasing rarity of IPv4 addresses, it is
    becoming harder for an operator to provide large contiguous
    address pools to CGNs.  Additionally, operational flexibility may
    require non-contiguous address pools for reasons such as
    differentiated services, routing management, etc.
    The reason for having SHOULD instead of MUST is to account for
    limitations imposed by available resources as well as constraints
    imposed for security reasons.
 REQ-4:  A CGN MUST support limiting the number of external ports (or,
    equivalently, "identifiers" for ICMP) that are assigned per
    subscriber.
    a.  Per-subscriber limits MUST be configurable by the CGN
        administrator.
    b.  Per-subscriber limits MAY be configurable independently per
        transport protocol.
    c.  Additionally, it is RECOMMENDED that the CGN include
        administrator-adjustable thresholds to prevent a single
        subscriber from consuming excessive CPU resources from the CGN
        (e.g., rate-limit the subscriber's creation of new mappings).
 Justification:  A CGN can be considered a network resource that is
    shared by competing subscribers.  Limiting the number of external
    ports assigned to each subscriber mitigates the denial-of-service
    (DoS) attack that a subscriber could launch against other
    subscribers through the CGN in order to get a larger share of the
    resource.  It ensures fairness among subscribers.  Limiting the
    rate of allocation mitigates a similar attack where the CPU is the
    resource being targeted instead of port numbers.  However, this
    requirement is not a MUST because it is very hard to explicitly
    call out all CPU-consuming events.
 REQ-5:  A CGN SHOULD support limiting the amount of state memory
    allocated per mapping and per subscriber.  This may include
    limiting the number of sessions, the number of filters, etc.,
    depending on the NAT implementation.
    a.  Limits SHOULD be configurable by the CGN administrator.
    b.  Additionally, it SHOULD be possible to limit the rate at which
        memory-consuming state elements are allocated.

Perreault, et al. Best Current Practice [Page 6] RFC 6888 CGN Requirements April 2013

 Justification:  A NAT needs to keep track of TCP sessions associated
    with each mapping.  This state consumes resources for which, in
    the case of a CGN, subscribers may compete.  It is necessary to
    ensure that each subscriber has access to a fair share of the
    CGN's resources.  Limiting the rate of allocation is intended to
    prevent CPU resource exhaustion.  Item "B" is at the SHOULD level
    to account for the fact that means other than rate limiting may be
    used to attain the same goal.
 REQ-6:  It MUST be possible to administratively turn off translation
    for specific destination addresses and/or ports.
 Justification:  It is common for a CGN administrator to provide
    access for subscribers to servers installed in the ISP's network
    in the external realm.  When such a server is able to reach the
    internal realm via normal routing (which is entirely controlled by
    the ISP), translation is unneeded.  In that case, the CGN may
    forward packets without modification, thus acting like a plain
    router.  This may represent an important efficiency gain.
    Figure 2 illustrates this use-case.
                X1:x1            X1':x1'            X2:x2
                +---+from X1:x1  +---+from X1:x1    +---+
                | C |  to X2:x2  |   |  to X2:x2    | S |
                | l |>>>>>>>>>>>>| C |>>>>>>>>>>>>>>| e |
                | i |            | G |              | r |
                | e |<<<<<<<<<<<<| N |<<<<<<<<<<<<<<| v |
                | n |from X2:x2  |   |from X2:x2    | e |
                | t |  to X1:x1  |   |  to X1:x1    | r |
                +---+            +---+              +---+
                      Figure 2: CGN Pass-Through
 REQ-7:  It is RECOMMENDED that a CGN use an "endpoint-independent
    filtering" behavior (as defined in Section 5 of [RFC4787]).  If it
    is known that "Address-Dependent Filtering" does not cause the
    application-layer protocol to break (how to determine this is out
    of scope for this document), then it MAY be used instead.
 Justification:  This is a stronger form of REQ-8 from [RFC4787].
    This is based on the observation that some games and peer-to-peer
    applications require EIF for the NAT traversal to work.  In the
    context of a CGN, it is important to minimize application
    breakage.

Perreault, et al. Best Current Practice [Page 7] RFC 6888 CGN Requirements April 2013

 REQ-8:  Once an external port is deallocated, it SHOULD NOT be
    reallocated to a new mapping until at least 120 seconds have
    passed, with the exceptions being:
    a.  If the CGN tracks TCP sessions (e.g., with a state machine, as
        in Section 3.5.2.2 of [RFC6146]), TCP ports MAY be reused
        immediately.
    b.  If external ports are statically assigned to internal
        addresses (e.g., address X with port range 1000-1999 is
        assigned to subscriber A, 2000-2999 to subscriber B, etc.),
        and the assignment remains constant across state loss, then
        ports MAY be reused immediately.
    c.  If the allocated external ports used address-dependent or
        address-and-port-dependent filtering before state loss, they
        MAY be reused immediately.
    The length of time and the maximum number of ports in this state
    MUST be configurable by the CGN administrator.
 Justification:  This is necessary in order to prevent collisions
    between old and new mappings and sessions.  It ensures that all
    established sessions are broken instead of redirected to a
    different peer.
    The exceptions are for cases where reusing a port immediately does
    not create a possibility that packets would be redirected to the
    wrong peer.  One can imagine other exceptions where mapping
    collisions are avoided, thus justifying the SHOULD level for this
    requirement.
    The 120 seconds value corresponds to the Maximum Segment Lifetime
    (MSL) from [RFC0793].
    Note that this requirement also applies to the case when a CGN
    loses state (due to a crash, reboot, failover to a cold standby,
    etc.).  In that case, ports that were in use at the time of state
    loss SHOULD NOT be reallocated until at least 120 seconds have
    passed.
 REQ-9:  A CGN MUST implement a protocol giving subscribers explicit
    control over NAT mappings.  That protocol SHOULD be the Port
    Control Protocol [RFC6887].
 Justification:  Allowing subscribers to manipulate the NAT state
    table with PCP greatly increases the likelihood that applications
    will function properly.

Perreault, et al. Best Current Practice [Page 8] RFC 6888 CGN Requirements April 2013

    A study of PCP-less CGN impacts can be found in [NAT444].  Another
    study considering the effects of PCP on a peer-to-peer file
    sharing protocol can be found in [BITTORRENT].
 REQ-10: CGN implementers SHOULD make their equipment manageable.
    Standards-based management using standards such as "Definitions of
    Managed Objects for NAT" [RFC4008] is RECOMMENDED.
 Justification:  It is anticipated that CGNs will be primarily
    deployed in ISP networks where the need for management is
    critical.  This requirement is at the SHOULD level to account for
    the fact that some CGN operators may not need management
    functionality.
    Note also that there are efforts within the IETF toward creating a
    MIB tailored for CGNs (e.g., [NAT-MIB]).
 REQ-11: When a CGN is unable to create a dynamic mapping due to
    resource constraints or administrative restrictions (i.e.,
    quotas):
    a.  it MUST drop the original packet;
    b.  it SHOULD send an ICMP Destination Unreachable message with
        code 1 (Host Unreachable) to the sender;
    c.  it SHOULD send a notification (e.g., SNMP trap) towards a
        management system (if configured to do so); and
    d.  it MUST NOT delete existing mappings in order to "make room"
        for the new one.  (This only applies to normal CGN behavior,
        not to manual operator intervention.)
 Justification:  This is a slightly different form of REQ-8 from
    [RFC5508].  Code 1 is preferred to code 13 because it is listed as
    a "soft error" in [RFC1122], which is important because we don't
    want TCP stacks to abort the connection attempt in this case.  See
    [RFC5461] for details on TCP's reaction to soft errors.
    Sending ICMP errors and SNMP traps may be rate-limited for
    security reasons, which is why requirements B and C are SHOULDs,
    not MUSTs.
    Applications generally handle connection establishment failure
    better than established connection failure.  This is why dropping
    the packet initiating the new connection is preferred over
    deleting existing mappings.  See also the rationale in Section 6
    of [RFC5508].

Perreault, et al. Best Current Practice [Page 9] RFC 6888 CGN Requirements April 2013

4. Logging

 It may be necessary for CGN administrators to be able to identify a
 subscriber based on external IPv4 address, port, and timestamp in
 order to deal with abuse.  When multiple subscribers share a single
 external address, the source address and port that are visible at the
 destination host have been translated from the ones originated by the
 subscriber.
 In order to be able to do this, the CGN would need to log the
 following information for each mapping created (this list is for
 informational purposes only and does not constitute a requirement):
 o  transport protocol
 o  subscriber identifier (e.g., internal source address or tunnel
    endpoint identifier)
 o  external source address
 o  external source port
 o  timestamp
 By "subscriber identifier" we mean information that uniquely
 identifies a subscriber.  For example, in a traditional NAT scenario,
 the internal source address would be sufficient.  In the case of DS-
 Lite, many subscribers share the same internal address and the
 subscriber identifier is the tunnel endpoint identifier (i.e., the
 B4's IPv6 address).
 A disadvantage of logging mappings is that CGNs under heavy usage may
 produce large amounts of logs, which may require large storage
 volume.
 REQ-12: A CGN SHOULD NOT log destination addresses or ports unless
    required to do so for administrative reasons.
 Justification:  Destination logging at the CGN creates privacy
    issues.  Furthermore, readers should be aware of logging
    recommendations for Internet-facing servers [RFC6302].  With
    compliant servers, the destination address and port do not need to
    be logged by the CGN.  This can help reduce the amount of logging.
    This requirement is at the SHOULD level to account for the fact
    that there may be other reasons for logging destination addresses
    or ports.  One such reason might be that the remote server is not
    following [RFC6302].

Perreault, et al. Best Current Practice [Page 10] RFC 6888 CGN Requirements April 2013

5. Port Allocation Scheme

 A CGN's port allocation scheme is subject to three competing
 requirements:
 REQ-13: A CGN's port allocation scheme SHOULD maximize port
    utilization.
 Justification:  External ports are one of the resources being shared
    by a CGN.  Efficient management of that resource directly impacts
    the quality of a subscriber's Internet connection.
    Some schemes are very efficient in their port utilization.  In
    that sense, they have good scaling properties (nothing is wasted).
    Others will systematically waste ports.
 REQ-14: A CGN's port allocation scheme SHOULD minimize log volume.
 Justification:  Huge log volumes can be problematic to CGN operators.
    Some schemes create one log entry per mapping.  Others allow
    multiple mappings to generate a single log entry, which sometimes
    can be expressed very compactly.  With some schemes, the logging
    frequency can approach that of DHCP servers.
 REQ-15: A CGN's port allocation scheme SHOULD make it hard for
    attackers to guess port numbers.
 Justification:  Easily guessed port numbers put subscribers at risk
    of the attacks described in [RFC6056].
    Some schemes provide very good security in that ports numbers are
    not easily guessed.  Others provide poor security to subscribers.
 A CGN implementation's choice of port allocation scheme optimizes to
 satisfy one requirement at the expense of another.  Therefore, these
 are soft requirements (SHOULD as opposed to MUST).

6. Deployment Considerations

 Several issues are encountered when CGNs are used [RFC6269].  There
 is current work in the IETF toward alleviating some of these issues.
 For example, see [NAT-REVEAL].

Perreault, et al. Best Current Practice [Page 11] RFC 6888 CGN Requirements April 2013

7. Security Considerations

 If a malicious subscriber can spoof another subscriber's CPE, it may
 cause a DoS to that subscriber by creating mappings up to the allowed
 limit.  An ISP can prevent this with ingress filtering, as described
 in [RFC2827].
 This document recommends endpoint-independent filtering (EIF) as the
 default filtering behavior for CGNs.  EIF has security considerations
 that are discussed in [RFC4787].
 NATs sometimes perform fragment reassembly.  CGNs would do so at
 presumably high data rates.  Therefore, the reader should be familiar
 with the potential security issues described in [RFC4963].

8. Acknowledgements

 Thanks for the input and review by Alexey Melnikov, Arifumi
 Matsumoto, Barry Leiba, Benson Schliesser, Dai Kuwabara, Dan Wing,
 Dave Thaler, David Harrington, Francis Dupont, Jean-Francois
 Tremblay, Joe Touch, Lars Eggert, Kousuke Shishikura, Mohamed
 Boucadair, Martin Stiemerling, Meng Wei, Nejc Skoberne, Pete Resnick,
 Reinaldo Penno, Ron Bonica, Sam Hartman, Sean Turner, Senthil
 Sivakumar, Stephen Farrell, Stewart Bryant, Takanori Mizuguchi,
 Takeshi Tomochika, Tina Tsou, Tomohiro Fujisaki, Tomohiro Nishitani,
 Tomoya Yoshida, Wes George, Wesley Eddy, and Yasuhiro Shirasaki.

9. References

9.1. Normative References

 [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
            Requirement Levels", BCP 14, RFC 2119, March 1997.
 [RFC4008]  Rohit, R., Srisuresh, P., Raghunarayan, R., Pai, N., and
            C. Wang, "Definitions of Managed Objects for Network
            Address Translators (NAT)", RFC 4008, March 2005.
 [RFC4787]  Audet, F. and C. Jennings, "Network Address Translation
            (NAT) Behavioral Requirements for Unicast UDP", BCP 127,
            RFC 4787, January 2007.
 [RFC5382]  Guha, S., Biswas, K., Ford, B., Sivakumar, S., and P.
            Srisuresh, "NAT Behavioral Requirements for TCP", BCP 142,
            RFC 5382, October 2008.

Perreault, et al. Best Current Practice [Page 12] RFC 6888 CGN Requirements April 2013

 [RFC5508]  Srisuresh, P., Ford, B., Sivakumar, S., and S. Guha, "NAT
            Behavioral Requirements for ICMP", BCP 148, RFC 5508,
            April 2009.
 [RFC5597]  Denis-Courmont, R., "Network Address Translation (NAT)
            Behavioral Requirements for the Datagram Congestion
            Control Protocol", BCP 150, RFC 5597, September 2009.
 [RFC6887]  Wing, D., Ed., Cheshire, S., Boucadair, M., Penno, R., and
            P.  Selkirk, "Port Control Protocol (PCP)", RFC 6887,
            April 2013.

9.2. Informative Reference

 [RFC0793]  Postel, J., "Transmission Control Protocol", STD 7, RFC
            793, September 1981.
 [RFC1122]  Braden, R., "Requirements for Internet Hosts -
            Communication Layers", STD 3, RFC 1122, October 1989.
 [RFC2663]  Srisuresh, P. and M. Holdrege, "IP Network Address
            Translator (NAT) Terminology and Considerations", RFC
            2663, August 1999.
 [RFC2827]  Ferguson, P. and D. Senie, "Network Ingress Filtering:
            Defeating Denial of Service Attacks which employ IP Source
            Address Spoofing", BCP 38, RFC 2827, May 2000.
 [RFC4963]  Heffner, J., Mathis, M., and B. Chandler, "IPv4 Reassembly
            Errors at High Data Rates", RFC 4963, July 2007.
 [RFC5461]  Gont, F., "TCP's Reaction to Soft Errors", RFC 5461,
            February 2009.
 [RFC6056]  Larsen, M. and F. Gont, "Recommendations for Transport-
            Protocol Port Randomization", BCP 156, RFC 6056, January
            2011.
 [RFC6146]  Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful
            NAT64: Network Address and Protocol Translation from IPv6
            Clients to IPv4 Servers", RFC 6146, April 2011.
 [RFC6264]  Jiang, S., Guo, D., and B. Carpenter, "An Incremental
            Carrier-Grade NAT (CGN) for IPv6 Transition", RFC 6264,
            June 2011.

Perreault, et al. Best Current Practice [Page 13] RFC 6888 CGN Requirements April 2013

 [RFC6269]  Ford, M., Boucadair, M., Durand, A., Levis, P., and P.
            Roberts, "Issues with IP Address Sharing", RFC 6269, June
            2011.
 [RFC6302]  Durand, A., Gashinsky, I., Lee, D., and S. Sheppard,
            "Logging Recommendations for Internet-Facing Servers", BCP
            162, RFC 6302, June 2011.
 [RFC6333]  Durand, A., Droms, R., Woodyatt, J., and Y. Lee, "Dual-
            Stack Lite Broadband Deployments Following IPv4
            Exhaustion", RFC 6333, August 2011.
 [NAT-MIB]  Perreault, S., Tsou, T., and S. Sivakumar, "Additional
            Managed Objects for Network Address Translators (NAT)",
            Work in Progress, February 2013.
 [NAT-REVEAL]
            Boucadair, M., Touch, J., Levis, P., and R. Penno,
            "Analysis of Solution Candidates to Reveal a Host
            Identifier (HOST_ID) in Shared Address Deployments", Work
            in Progress, April 2013.
 [NAT444]   Donley, C., Ed., Howard, L., Kuarsingh, V., Berg, J., and
            J. Doshi, "Assessing the Impact of Carrier-Grade NAT on
            Network Applications", Work in Progress, April 2013.
 [BITTORRENT]
            Boucadair, M., Zheng, T., Deng, X., and J. Queiroz,
            "Behavior of BitTorrent service in PCP-enabled networks
            with Address Sharing", Work in Progress, May 2012.

Authors' Addresses

 Simon Perreault (editor)
 Viagenie
 246 Aberdeen
 Quebec, QC  G1R 2E1
 Canada
 Phone: +1 418 656 9254
 EMail: simon.perreault@viagenie.ca
 URI:   http://www.viagenie.ca

Perreault, et al. Best Current Practice [Page 14] RFC 6888 CGN Requirements April 2013

 Ikuhei Yamagata
 NTT Communications Corporation
 Gran Park Tower 17F, 3-4-1 Shibaura, Minato-ku
 Tokyo  108-8118
 Japan
 Phone: +81 50 3812 4704
 EMail: ikuhei@nttv6.jp
 Shin Miyakawa
 NTT Communications Corporation
 Gran Park Tower 17F, 3-4-1 Shibaura, Minato-ku
 Tokyo  108-8118
 Japan
 Phone: +81 50 3812 4695
 EMail: miyakawa@nttv6.jp
 Akira Nakagawa
 Japan Internet Exchange Co., Ltd. (JPIX)
 Otemachi Building 21F, 1-8-1 Otemachi, Chiyoda-ku
 Tokyo  100-0004
 Japan
 Phone: +81 90 9242 2717
 EMail: a-nakagawa@jpix.ad.jp
 Hiroyuki Ashida
 Cisco Systems
 Midtown Tower, 9-7-1, Akasaka
 Minato-Ku, Tokyo  107-6227
 Japan
 EMail: hiashida@cisco.com

Perreault, et al. Best Current Practice [Page 15]

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