Reflections on Internet Transparency
RFC 4924

Network Working Group                                      B. Aboba, Ed.
Request for Comment: 4924                                      E. Davies
Category: Informational                      Internet Architecture Board
                                                               July 2007

                  Reflections on Internet Transparency

Status of This Memo

   This memo provides information for the Internet community.  It does
   not specify an Internet standard of any kind.  Distribution of this
   memo is unlimited.

Copyright Notice

   Copyright (C) The IETF Trust (2007).

Abstract

   This document provides a review of previous IAB statements on
   Internet transparency, as well a discussion of new transparency
   issues.  Far from having lessened in relevance, technical
   implications of intentionally or inadvertently impeding network
   transparency play a critical role in the Internet's ability to
   support innovation and global communication.  This document provides
   some specific illustrations of those potential impacts.

Table of Contents

   1. Introduction ....................................................2
   2. Additional Transparency Issues ..................................4
      2.1. Application Restriction ....................................4
      2.2. Quality of Service (QoS) ...................................6
      2.3. Application Layer Gateways (ALGs) ..........................7
      2.4. IPv6 Address Restrictions ..................................8
           2.4.1. Allocation of IPv6 Addresses by Providers ...........8
           2.4.2. IKEv2 ...............................................8
      2.5. DNS Issues .................................................9
           2.5.1. Unique Root .........................................9
           2.5.2. Namespace Mangling ..................................9
      2.6. Load Balancing and Redirection ............................10
   3. Security Considerations ........................................11
   4. References .....................................................11
      4.1. Informative References ....................................11
   Acknowledgments ...................................................13
   Appendix A - IAB Members at the Time of Approval ..................14

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1.  Introduction

   In the past, the IAB has published a number of documents relating to
   Internet transparency and the end-to-end principle, and other IETF
   documents have also touched on these issues as well.  These documents
   articulate the general principles on which the Internet architecture
   is based, as well as the core values that the Internet community
   seeks to protect going forward.  This document reaffirms those
   principles, describes the concept of "oblivious transport" as
   developed in the DARPA NewArch project [NewArch], and addresses a
   number of new transparency issues.

   A network that does not filter or transform the data that it carries
   may be said to be "transparent" or "oblivious" to the content of
   packets.  Networks that provide oblivious transport enable the
   deployment of new services without requiring changes to the core.  It
   is this flexibility that is perhaps both the Internet's most
   essential characteristic as well as one of the most important
   contributors to its success.

   "Architectural Principles of the Internet" [RFC1958], Section 2
   describes the core tenets of the Internet architecture:

      However, in very general terms, the community believes that the
      goal is connectivity, the tool is the Internet Protocol, and the
      intelligence is end to end rather than hidden in the network.

      The current exponential growth of the network seems to show that
      connectivity is its own reward, and is more valuable than any
      individual application such as mail or the World-Wide Web.  This
      connectivity requires technical cooperation between service
      providers, and flourishes in the increasingly liberal and
      competitive commercial telecommunications environment.

   "The Rise of the Middle and the Future of End-to-End:  Reflections on
   the Evolution of the Internet Architecture" [RFC3724], Section 4.1.1
   describes some of the desirable consequences of this approach:

      One desirable consequence of the end-to-end principle is
      protection of innovation.  Requiring modification in the network
      in order to deploy new services is still typically more difficult
      than modifying end nodes.  The counterargument - that many end
      nodes are now essentially closed boxes which are not updatable and
      that most users don't want to update them anyway - does not apply
      to all nodes and all users.  Many end nodes are still user
      configurable and a sizable percentage of users are "early
      adopters," who are willing to put up with a certain amount of
      technological grief in order to try out a new idea.  And, even for

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      the closed boxes and uninvolved users, downloadable code that
      abides by the end-to-end principle can provide fast service
      innovation.  Requiring someone with a new idea for a service to
      convince a bunch of ISPs or corporate network administrators to
      modify their networks is much more difficult than simply putting
      up a Web page with some downloadable software implementing the
      service.

   Yet, even while the Internet has greatly expanded both in size and in
   application diversity, the degree of transparency has diminished.
   "Internet Transparency" [RFC2775] notes some of the causes for the
   loss of Internet transparency and analyzes their impact.  This
   includes discussion of Network Address Translators (NATs), firewalls,
   application level gateways (ALGs), relays, proxies, caches, split
   Domain Name Service (DNS), load balancers, etc.  [RFC2775] also
   analyzes potential future directions that could lead to the
   restoration of transparency.  Section 6 summarizes the conclusions:

      Although the pure IPv6 scenario is the cleanest and simplest, it
      is not straightforward to reach it.  The various scenarios without
      use of IPv6 are all messy and ultimately seem to lead to dead ends
      of one kind or another.  Partial deployment of IPv6, which is a
      required step on the road to full deployment, is also messy but
      avoids the dead ends.

   While full restoration of Internet transparency through the
   deployment of IPv6 remains a goal, the Internet's growing role in
   society, the increasing diversity of applications, and the continued
   growth in security threats has altered the balance between
   transparency and security, and the disparate goals of interested
   parties make these tradeoffs inherently complex.

   While transparency provides great flexibility, it also makes it
   easier to deliver unwanted as well as wanted traffic.  Unwanted
   traffic is increasingly cited as a justification for limiting
   transparency.  If taken to its logical conclusion, this argument will
   lead to the development of ever more complex transparency barriers to
   counter increasingly sophisticated security threats.  Transparency,
   once lost, is hard to regain, so that such an approach, if
   unsuccessful, would lead to an Internet that is both insecure and
   lacking in transparency.  The alternative is to develop increasingly
   sophisticated host-based security mechanisms; while such an approach
   may also fail to keep up with increasingly sophisticated security
   threats, it is less likely to sacrifice transparency in the process.

   Since many of the fundamental forces that have led to a reduction in
   the transparency of the IPv4 Internet also may play a role in the
   IPv6 Internet, the transparency of the IPv6 Internet is not pre-

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   ordained, but rather represents an ideal whose maintenance will
   require significant ongoing effort.

   As noted in [NewArch], the technical cooperation that once
   characterized the development of the Internet has increasingly given
   way to a tussle between the interests of subscribers, vendors,
   providers, and society at large.  Oblivious transport may be desired
   by developers seeking to deploy new services; providers may desire to
   block unwanted traffic in the core before it impacts subscribers;
   vendors and providers may wish to enable delivery of "value added"
   services in the network that enable them to differentiate their
   offerings; subscribers may be sympathetic to either point of view,
   depending on their interests; society at large may wish to block
   "offensive" material and monitor traffic that shows malicious intent.

   While there is no architectural "fix" that can restore oblivious
   transport while satisfying the interests of all parties, it is
   possible for providers to provide subscribers with information about
   the nature of the services being provided.  Subscribers need to be
   aware of whether they are receiving oblivious transport, and if not,
   how the service affects their traffic.

   Since the publication of the previously cited IAB statements, new
   technologies have been developed, and views on existing technology
   have changed.  In some cases, these new technologies impact oblivious
   transport, and subscribers need to be aware of the implications for
   their service.

2.  Additional Transparency Issues

2.1.  Application Restriction

   Since one of the virtues of the Internet architecture is the ease
   with which new applications can be deployed, practices that restrict
   the ability to deploy new applications have the potential to reduce
   innovation.

   One such practice is filtering designed to block or restrict
   application usage, implemented without customer consent.  This
   includes Internet, Transport, and Application layer filtering
   designed to block or restrict traffic associated with one or more
   applications.

   While provider filtering may be useful to address security issues
   such as attacks on provider infrastructure or denial of service
   attacks, greater flexibility is provided by allowing filtering to be
   determined by the customer.  Typically, this would be implemented at
   the edges, such as within provider access routers (e.g., outsourced

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   firewall services), customer premise equipment (e.g., access
   firewalls), or on hosts (e.g., host firewalls).  Deployment of
   filtering at the edges provides customers with the flexibility to
   choose which applications they wish to block or restrict, whereas
   filtering in the core may not permit hosts to communicate, even when
   the communication would conform to the appropriate use policies of
   the administrative domains to which those hosts belong.

   In practice, filtering intended to block or restrict application
   usage is difficult to successfully implement without customer
   consent, since over time developers will tend to re-engineer filtered
   protocols so as to avoid the filters.  Thus over time, filtering is
   likely to result in interoperability issues or unnecessary
   complexity.  These costs come without the benefit of effective
   filtering since many application protocols began to use HTTP as a
   transport protocol after application developers observed that
   firewalls allow HTTP traffic while dropping packets for unknown
   protocols.

   In addition to architectural concerns, filtering to block or restrict
   application usage also raises issues of disclosure and end-user
   consent.  As pointed out in "Terminology for Describing Internet
   Connectivity" [RFC4084], services advertised as providing "Internet
   connectivity" differ considerably in their capabilities, leading to
   confusion.  The document defines terminology relating to Internet
   connectivity, including "Web connectivity", "Client connectivity
   only, without a public address", "Client only, public address",
   "Firewalled Internet Connectivity", and "Full Internet Connectivity".
   With respect to "Full Internet Connectivity" [RFC4084], Section 2
   notes:

      Filtering Web proxies, interception proxies, NAT, and other
      provider-imposed restrictions on inbound or outbound ports and
      traffic are incompatible with this type of service.  Servers ...
      are typically considered normal.  The only compatible restrictions
      are bandwidth limitations and prohibitions against network abuse
      or illegal activities.

   [RFC4084], Section 4 describes disclosure obligations that apply to
   all forms of service limitation, whether applied on outbound or
   inbound traffic:

      More generally, the provider should identify any actions of the
      service to block, restrict, or alter the destination of, the
      outbound use (i.e., the use of services not supplied by the
      provider or on the provider's network) of applications services.

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   In essence, [RFC4084] calls for providers to declare the ways in
   which the service provided departs from oblivious transport.  Since
   the lack of oblivious transport within transit networks will also
   affect transparency, this also applies to providers over whose
   network the subscriber's traffic may travel.

2.2.  Quality of Service (QoS)

   While [RFC4084] notes that bandwidth limitations are compatible with
   "Full Internet Connectivity", in some cases QoS restrictions may go
   beyond simple average or peak bandwidth limitations.  When used to
   restrict the ability to deploy new applications, QoS mechanisms are
   incompatible with "Full Internet Connectivity" as defined in
   [RFC4084].  The disclosure and consent obligations referred to in
   [RFC4084], Section 4 also apply to QoS mechanisms.

   Deployment of QoS technology has potential implications for Internet
   transparency, since the QoS experienced by a flow can make the
   Internet more or less oblivious to that flow.  While QoS support is
   highly desirable in order for real-time services to coexist with
   elastic services, it is not without impact on packet delivery.

   Specifically, QoS classes such as "default" [RFC2474] or "lower
   effort" [RFC3662] may experience higher random-loss rates than others
   such as "assured forwarding" [RFC2597].  Conversely, bandwidth-
   limited QoS classes such as "expedited forwarding" [RFC3246] may
   experience systematic packet loss if they exceed their assigned
   bandwidth.  Other QoS mechanisms such as load balancing may have
   side-effects such as re-ordering of packets, which may have a serious
   impact on perceived performance.

   QoS implementations that reduce the ability to deploy new
   applications on the Internet are similar in effect to other
   transparency barriers.  Since arbitrary or severe bandwidth
   limitations can make an application unusable, the introduction of
   application-specific bandwidth limitations is equivalent to
   application blocking or restriction from a user's standpoint.

   Using QoS mechanisms to discriminate against traffic not matching a
   set of services or addresses has a similar effect to deployment of a
   highly restrictive firewall.  Requiring an authenticated RSVP
   reservation [RFC2747][RFC3182] for a flow to avoid severe packet loss
   has a similar effect to deployment of authenticated firewall
   traversal.

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   As with filtering, there may be valid uses for customer-imposed QoS
   restrictions.  For example, a customer may wish to limit the
   bandwidth consumed by peer-to-peer file sharing services, so as to
   limit the impact on mission-critical applications.

2.3.  Application Layer Gateways (ALGs)

   The IAB has devoted considerable attention to Network Address
   Translation (NAT), so that there is little need to repeat that
   discussion here.  However, with the passage of time, it has become
   apparent that there are problems inherent in the deployment of
   Application Layer Gateways (ALGs) (frequently embedded within
   firewalls and devices implementing NAT).

   [RFC2775], Section 3.5 states:

      If the full range of Internet applications is to be used, NATs
      have to be coupled with application level gateways (ALGs) or
      proxies.  Furthermore, the ALG or proxy must be updated whenever a
      new address-dependent application comes along.  In practice, NAT
      functionality is built into many firewall products, and all useful
      NATs have associated ALGs, so it is difficult to disentangle their
      various impacts.

   With the passage of time and development of NAT traversal
   technologies such as IKE NAT-T [RFC3947], Teredo [RFC4380], and STUN
   [RFC3489], it has become apparent that ALGs represent an additional
   barrier to transparency.  In addition to posing barriers to the
   deployment of new applications not yet supported by ALGs, ALGs may
   create difficulties in the deployment of existing applications as
   well as updated versions.  For example, in the development of IKE
   NAT-T, additional difficulties were presented by "IPsec Helper" ALGs
   embedded within NATs.

   It should be stressed that these difficulties are inherent in the
   architecture of ALGs, rather than merely an artifact of poor
   implementations.  No matter how well an ALG is implemented, barriers
   to transparency will emerge over time, so that the notion of a
   "transparent ALG" is a contradiction in terms.

   In particular, DNS ALGs present a host of issues, including
   incompatibilities with DNSSEC that prevent deployment of a secure
   naming infrastructure even if all the endpoints are upgraded.  For
   details, see "Reasons to Move the Network Address Translator -
   Protocol Translator (NAT-PT) to Historic Status" [RFC4966], Section
   3.

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2.4.  IPv6 Address Restrictions

   [RFC2775], Section 5.1 states:

      Note that it is a basic assumption of IPv6 that no artificial
      constraints will be placed on the supply of addresses, given that
      there are so many of them.  Current practices by which some ISPs
      strongly limit the number of IPv4 addresses per client will have
      no reason to exist for IPv6.

   Constraints on the supply of IPv6 addresses provide an incentive for
   the deployment of NAT with IPv6.  The introduction of NAT for IPv6
   would represent a barrier to transparency, and therefore is to be
   avoided if at all possible.

2.4.1.  Allocation of IPv6 Addresses by Providers

   In order to encourage deployments of IPv6 to provide oblivious
   transport, it is important that IPv6 networks of all sizes be
   supplied with a prefix sufficient to enable allocation of addresses
   and sub-networks for all the hosts and links within their network.
   Initial address allocation policy suggested allocating a /48 prefix
   to "small" sites, which should handle typical requirements.  Any
   changes to allocation policy should take into account the
   transparency reduction that will result from further restriction.
   For example, provider provisioning of a single /64 without support
   for prefix delegation or (worse still) a longer prefix (prohibited by
   [RFC4291], Section 2.5.4 for non-000/3 unicast prefixes) would
   represent a restriction on the availability of IPv6 addresses that
   could represent a barrier to transparency.

2.4.2.  IKEv2

   Issues with IPv6 address assignment mechanisms in IKEv2 [RFC4306] are
   described in [RFC4718]:

      IKEv2 also defines configuration payloads for IPv6.  However, they
      are based on the corresponding IPv4 payloads, and do not fully
      follow the "normal IPv6 way of doing things"...  In particular,
      IPv6 stateless autoconfiguration or router advertisement messages
      are not used; neither is neighbor discovery.

   IKEv2 provides for the assignment of a single IPv6 address, using the
   INTERNAL_IP6_ADDRESS attribute.  If this is the only attribute
   supported for IPv6 address assignment, then only a single IPv6
   address will be available.  The INTERNAL_IP6_SUBNET attribute enables
   the host to determine the sub-networks accessible directly through
   the secure tunnel created; it could potentially be used to assign one

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   or more prefixes to the IKEv2 initiator that could be used for
   address creation.

   However, this does not enable the host to obtain prefixes that can be
   delegated.  The INTERNAL_IP6_DHCP attribute provides the address of a
   DHCPv6 server, potentially enabling use of DHCPv6 prefix delegation
   [RFC3633] to obtain additional prefixes.  However, in order for
   implementers to utilize these options in an interoperable way,
   clarifications to the IKEv2 specification appear to be needed.

2.5.  DNS Issues

2.5.1.  Unique Root

   In "IAB Technical Comment on the Unique DNS Root" [RFC2826], the
   technical arguments for a unique root were presented.

   One of the premises in [RFC2826] is that a common namespace and
   common semantics applied to these names is needed for effective
   communication between two parties.  The document argues that this
   principle can only be met when one unique root is being used and when
   the domains are maintained by single owners or maintainers.

   Because [RFC4084] targets only IP service terms and does not talk
   about namespace issues, it does not refer to [RFC2826].  We stress
   that the use of a unique root for the DNS namespace is essential for
   proper IP service.

2.5.2.  Namespace Mangling

   Since the publication of [RFC2826], there have been reports of
   providers implementing recursive nameservers and/or DNS forwarders
   that replace answers that indicate that a name does not exist in the
   DNS hierarchy with a name and an address record that hosts a Web
   service that is supposed to be useful for end-users.

   The effect of this modification is similar to placement of a wildcard
   in top-level domains.  Although wildcard labels in top-level domains
   lead to problems that are described elsewhere (such as "The Role of
   Wildcards in the Domain Name System" [RFC4592]), they do not strictly
   violate the DNS protocol.  This is not the case where modification of
   answers takes place in the middle of the path between authoritative
   servers and the stub resolvers that provide the answers to
   applications.

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   [RFC2826] section 1.3 states:

      Both the design and implementations of the DNS protocol are
      heavily based on the assumption that there is a single owner or
      maintainer for every domain, and that any set of resources records
      associated with a domain is modified in a single-copy serializable
      fashion.

   In particular, the DNSSEC protocol described in "Protocol
   Modifications for the DNS Security Extensions" [RFC4035] has been
   designed to verify that DNS information has not been modified between
   the moment they have been published on an authoritative server and
   the moment the validation takes place.  Since that verification can
   take place at the application level, any modification by a recursive
   forwarder or other intermediary will cause validation failures,
   disabling the improved security that DNSSEC is intended to provide.

2.6.  Load Balancing and Redirection

   In order to provide information that is adapted to the locale from
   which a request is made or to provide a speedier service, techniques
   have been deployed that result in packets being redirected or taking
   a different path depending on where the request originates.  For
   example, requests may be distributed among servers using "reverse
   NAT" (which modifies the destination rather than the source address);
   responses to DNS requests may be altered; HTTP "gets" may be re-
   directed; or specific packets may be diverted onto overlay networks.

   Provided that these services are well-implemented, they can provide
   value; however, transparency reduction or service disruption can also
   result:

   [1] The use of "reverse NAT" to balance load among servers supporting
       IPv6 would adversely affect the transparency of the IPv6
       Internet.

   [2] DNS re-direction is typically based on the source address of the
       query, which may not provide information on the location of the
       host originating the query.  As a result, a host configured with
       the address of a distant DNS server could find itself pointed to
       a server near the DNS server, rather than a server near the host.
       HTTP re-direction does not encounter this issue.

   [3] If the packet filters that divert packets onto overlay networks
       are misconfigured, this can lead to packets being misdirected
       onto the overlay and delayed or lost if the far end cannot return
       them to the global Internet.

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   [4] The use of anycast needs to be carefully thought out so that
       service can be maintained in the face of routing changes.

3.  Security Considerations

   Several transparency issues discussed in this document (NATs,
   transparent proxies, DNS namespace mangling) weaken existing end-to-
   end security guarantees and interfere with the deployment of
   protocols that would strengthen end-to-end security.

   [RFC2775], Section 7 states:

      The loss of transparency at the Intranet/Internet boundary may be
      considered a security feature, since it provides a well defined
      point at which to apply restrictions.  This form of security is
      subject to the "crunchy outside, soft inside" risk, whereby any
      successful penetration of the boundary exposes the entire Intranet
      to trivial attack.  The lack of end-to-end security applied within
      the Intranet also ignores insider threats.

   Today, malware has evolved to increasingly take advantage of the
   application-layer as a rich and financially attractive source of
   security vulnerabilities, as well as a mechanism for penetration of
   the Intranet/Internet boundary.  This has lessened the security value
   of existing transparency barriers and made it increasingly difficult
   to prevent the propagation of malware without imposing restrictions
   on application behavior.  However, as with other approaches to
   application restriction (see Section 2.1), these limitations are most
   flexibly imposed at the edge.

4.  References

4.1.  Informative References

   [NewArch] Clark, D. et al.,  "New Arch: Future Generation Internet
             Architecture",
             http://www.isi.edu/newarch/iDOCS/final.finalreport.pdf

   [RFC1958] Carpenter, B., Ed., "Architectural Principles of the
             Internet", RFC 1958, June 1996.

   [RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black,
             "Definition of the Differentiated Services Field (DS Field)
             in the IPv4 and IPv6 Headers", RFC 2474, December 1998.

   [RFC2597] Heinanen, J., Baker, F., Weiss, W., and J. Wroclawski,
             "Assured Forwarding PHB Group", RFC 2597, June 1999.

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   [RFC2747] Baker, F., Lindell, B., and M. Talwar, "RSVP Cryptographic
             Authentication", RFC 2747, January 2000.

   [RFC2775] Carpenter, B., "Internet Transparency", RFC 2775, February
             2000.

   [RFC2826] Internet Architecture Board, "IAB Technical Comment on the
             Unique DNS Root", RFC 2826, May 2000.

   [RFC3182] Yadav, S., Yavatkar, R., Pabbati, R., Ford, P., Moore, T.,
             Herzog, S., and R. Hess, "Identity Representation for
             RSVP", RFC 3182, October 2001.

   [RFC3246] Davie, B., Charny, A., Bennet, J., Benson, K., Le Boudec,
             J., Courtney, W., Davari, S., Firoiu, V., and D. Stiliadis,
             "An Expedited Forwarding PHB (Per-Hop Behavior)", RFC 3246,
             March 2002.

   [RFC3489] Rosenberg, J., Weinberger, J., Huitema, C., and R. Mahy,
             "STUN - Simple Traversal of User Datagram Protocol (UDP)
             Through Network Address Translators (NATs)", RFC 3489,
             March 2003.

   [RFC3633] Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic
             Host Configuration Protocol (DHCP) version 6", RFC 3633,
             December 2003.

   [RFC3662] Bless, R., Nichols, K., and K. Wehrle, "A Lower Effort
             Per-Domain Behavior (PDB) for Differentiated Services", RFC
             3662, December 2003.

   [RFC3724] Kempf, J., Ed., Austein, R., Ed., and IAB, "The Rise of the
             Middle and the Future of End-to-End: Reflections on the
             Evolution of the Internet Architecture", RFC 3724, March
             2004.

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

   [RFC4035] Arends, R., Austein, R., Larson, M., Massey, D., and S.
             Rose, "Protocol Modifications for the DNS Security
             Extensions", RFC 4035, March 2005.

   [RFC4084] Klensin, J., "Terminology for Describing Internet
             Connectivity", BCP 104, RFC 4084, May 2005.

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   [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
             Architecture", RFC 4291, February 2006.

   [RFC4306] Kaufman, C., Ed., "Internet Key Exchange (IKEv2) Protocol",
             RFC 4306, December 2005.

   [RFC4380] Huitema, C., "Teredo: Tunneling IPv6 over UDP through
             Network Address Translations (NATs)", RFC 4380, February
             2006.

   [RFC4592] Lewis, E., "The Role of Wildcards in the Domain Name
             System", RFC 4592, July 2006.

   [RFC4718] Eronen, P. and P. Hoffman, "IKEv2 Clarifications and
             Implementation Guidelines", RFC 4718, October 2006.

   [RFC4966] Aoun, C. and E. Davies, "Reasons to Move the Network
             Address Translator - Protocol Translator (NAT-PT) to
             Historic Status", RFC 4966, July 2007.

Acknowledgments

   The authors would like to acknowledge Jari Arkko, Stephane
   Bortzmeyer, Brian Carpenter, Spencer Dawkins, Stephen Kent, Carl
   Malamud, Danny McPherson, Phil Roberts and Pekka Savola for
   contributions to this document.

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Appendix A - IAB Members at the Time of Approval

   Bernard Aboba
   Loa Andersson
   Brian Carpenter
   Leslie Daigle
   Elwyn Davies
   Kevin Fall
   Olaf Kolkman
   Kurtis Lindqvist
   David Meyer
   David Oran
   Eric Rescorla
   Dave Thaler
   Lixia Zhang

Authors' Addresses

   Bernard Aboba
   Microsoft Corporation
   One Microsoft Way
   Redmond, WA 98052

   EMail: bernarda@microsoft.com
   Phone: +1 425 706 6605
   Fax:   +1 425 936 7329

   Elwyn B. Davies
   Consultant
   Soham, Cambs
   UK

   Phone: +44 7889 488 335
   EMail: elwynd@dial.pipex.com

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Full Copyright Statement

   Copyright (C) The IETF Trust (2007).

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