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Versions: 00 01 draft-ietf-v6ops-v6-aaaa-whitelisting-implications

Internet Engineering Task Force                             J. Livingood
Internet-Draft                                                   Comcast
Intended status: Informational                          October 22, 2010
Expires: April 25, 2011


                IPv6 AAAA DNS Whitelisting Implications
            draft-livingood-dns-whitelisting-implications-01

Abstract

   The objective of this document is to describe what whitelisting of
   DNS AAAA resource records is, or DNS whitelisting for short, as well
   as what the implications of this emerging practice are and what
   alternatives may exist.  The audience for this document is the
   Internet community generally, including the IETF and IPv6
   implementers.

Status of this Memo

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

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

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

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

Copyright Notice

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

   This document is subject to BCP 78 and the IETF Trust's Legal
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   publication of this document.  Please review these documents
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   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as



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   described in the Simplified BSD License.

   This document may contain material from IETF Documents or IETF
   Contributions published or made publicly available before November
   10, 2008.  The person(s) controlling the copyright in some of this
   material may not have granted the IETF Trust the right to allow
   modifications of such material outside the IETF Standards Process.
   Without obtaining an adequate license from the person(s) controlling
   the copyright in such materials, this document may not be modified
   outside the IETF Standards Process, and derivative works of it may
   not be created outside the IETF Standards Process, except to format
   it for publication as an RFC or to translate it into languages other
   than English.






































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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
   2.  How DNS Whitelisting Works . . . . . . . . . . . . . . . . . .  5
   3.  Concerns Regarding DNS Whitelisting  . . . . . . . . . . . . .  7
   4.  Similarities to Split DNS  . . . . . . . . . . . . . . . . . .  9
   5.  Likely Deployment Scenarios  . . . . . . . . . . . . . . . . . 10
     5.1.  Deploying DNS Whitelisting Universally . . . . . . . . . . 10
     5.2.  Deploying DNS Whitelisting On An Ad Hoc Basis  . . . . . . 11
   6.  What Problems Are DNS Whitelisting Implementers Trying To
       Solve? . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
   7.  Implications of DNS Whitelisting . . . . . . . . . . . . . . . 12
     7.1.  Architectural Implications . . . . . . . . . . . . . . . . 12
     7.2.  Public IPv6 Address Reachability Implications  . . . . . . 13
     7.3.  Operational Implications . . . . . . . . . . . . . . . . . 13
       7.3.1.  De-Whitelisting May Occur  . . . . . . . . . . . . . . 13
       7.3.2.  Authoritative DNS Server Operational Implications  . . 13
       7.3.3.  DNS Recursive Resolver Server Operational
               Implications . . . . . . . . . . . . . . . . . . . . . 14
       7.3.4.  Monitoring Implications  . . . . . . . . . . . . . . . 15
       7.3.5.  Troubleshooting Implications . . . . . . . . . . . . . 15
       7.3.6.  Additional Implications If Deployed On An Ad Hoc
               Basis  . . . . . . . . . . . . . . . . . . . . . . . . 16
     7.4.  Homogeneity May Be Encouraged  . . . . . . . . . . . . . . 16
     7.5.  Technology Policy Implications . . . . . . . . . . . . . . 17
     7.6.  IPv6 Adoption Implications . . . . . . . . . . . . . . . . 18
   8.  Solutions  . . . . . . . . . . . . . . . . . . . . . . . . . . 18
     8.1.  Implement DNS Whitelisting Universally . . . . . . . . . . 18
     8.2.  Implement DNS Whitelisting On An Ad Hoc Basis  . . . . . . 18
     8.3.  Do Not Implement DNS Whitelisting  . . . . . . . . . . . . 19
       8.3.1.  Solving Current End User IPv6 Impairments  . . . . . . 19
   9.  Security Considerations  . . . . . . . . . . . . . . . . . . . 19
     9.1.  DNSSEC Considerations  . . . . . . . . . . . . . . . . . . 20
     9.2.  Authoritative DNS Response Consistency Considerations  . . 20
   10. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 20
   11. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 20
   12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 21
   13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 21
     13.1. Normative References . . . . . . . . . . . . . . . . . . . 21
     13.2. Informative References . . . . . . . . . . . . . . . . . . 22
   Appendix A.  Document Change Log . . . . . . . . . . . . . . . . . 22
   Appendix B.  Open Issues . . . . . . . . . . . . . . . . . . . . . 23
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 23








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1.  Introduction

   [EDITORIAL: This is a rough first -00 draft.  Some sections have not
   yet been completed but will be soon.  Suggestions on all parts of
   this document are eagerly solicited.]

   This document describes the emerging practice of whitelisting of DNS
   AAAA resource records (RRs), or DNS whitelisting for short.  It also
   explores the implications of this emerging practice are and what
   alternatives may exist.

   The practice of DNS whitelisting appears to have first been used by
   major web content sites.  These web site operators observed that when
   they added AAAA RRs to their authoritative DNS servers that a small
   fraction of end users had slow or otherwise impaired access to a
   given web site with both AAAA and A RRs.  The fraction of users with
   such impaired access has been estimated to be roughly 0.078% of total
   Internet users [IETF 77 DNSOP WG Presentation] [Network World Article
   on IETF 77 DNSOP WG Presentation].  Thus, in an example Internet
   Service Provider (ISP) network of 10 million users, approximately
   7,800 of those users may experience such impaired access.

   As a result of this impairment affecting end users of a given domain,
   a few large web site operators have begun to either implement DNS
   whitelisting or strongly consider the implementation of DNS
   whitelisting [Network World Article on DNS Whitelisting].  When
   implemented, DNS whitelisting in practice means that a domain's
   authoritative DNS will return a AAAA RR to DNS recursive resolvers
   [RFC1035] on the whitelist, while returning no AAAA RRs to DNS
   resolvers which are not on the whitelist.  It is important to note
   that these web site operators are motivated to maintain a high-
   quality user experience for all of their users, and that they are
   attempting to shield users with impaired access from the symptoms of
   these impairments that would negatively affect their access to
   certain websites and related Internet resources.

   [EDITORIAL: change web site operators --> domain operators?]

   However, critics of this emerging practice of DNS whitelisting have
   articulated several concerns.  Among these are that this is a very
   different behavior from the current practice concerning the
   publishing of IPv4 address records, that it may create a two-tiered
   Internet, that policies concerning whitelisting and de-whitelisting
   are opaque, that DNS whitelisting reduces interest in the deployment
   of IPv6, that new operational and management burdens are created, and
   that the costs and negative implications of DNS whitelisting outweigh
   the perceived benefits as compared to fixing underlying impairments.




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   This document explores the reasons and motivations for DNS
   whitelisting.  It also explores the concerns regarding this emerging
   practice.  As a result, readers can hopefully better understand what
   DNS whitelisting is, why some parties are implementing it, and why
   other parties are critical of the practice.


2.  How DNS Whitelisting Works

   DNS whitelisting is implemented in authoritative DNS servers, where
   those servers implement IP address-based restrictions on AAAA query
   responses, which contain IPv6 addresses.  In practice DNS
   whitelisting has been primarily implemented by web server operators.
   For a given operator of the website www.example.com, that operator
   essentially applies an access control list (ACL) on their
   authoritative DNS servers, which are authoritative for the domain
   example.com.  The ACL is then configured with the IPv4 and/or IPv6
   addresses of DNS recursive resolvers on the Internet, which have been
   authorized to be added to the ACL and to therefore receive AAAA RR
   responses.  These DNS recursive resolvers are operated by other
   parties, such as ISPs, universities, governments, businesses,
   individual end users, etc.  If a DNS recursive resolver IS NOT on the
   ACL, then NO AAAA RRs with IPv6 addresses will be sent in response to
   a query for a given hostname in the example.com domain.  However, if
   a DNS recursive resolver IS on the ACL, then AAAA RRs with IPv6
   addresses will be sent in response to a query for a given hostname in
   the example.com domain.

   In practice this generally means that a very small fraction of the
   DNS recursive resolvers on the Internet can receive AAAA responses
   with IPv6 addresses, which means that the large majority of DNS
   resolvers on the Internet will receive only A RRs with IPv4
   addresses.  Thus, quite simply, the authoritative server hands out
   different answers depending upon who is asking; with IPv4 and IPv6
   records for some on the authorized whitelist, and only IPv4 records
   for everyone else.  See Figure 1 and Figure 2 for two different
   visual descriptions of how this works in practice.

   Finally, DNS whitelisting can be deployed in two primary ways:
   universally on a global basis, or on an ad hoc basis.  These two
   potential deployment models are described in Section 5.










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   1: The authoritative DNS server for example.com receives a DNS
      query for www.example.com, for which both A (IPv4) and AAAA
      (IPv6) address records exist.
   2: The authoritative DNS server examines the IP address of the DNS
      recursive resolver sending the query.
   3: The authoritative DNS server checks this IP address against the
      access control list (ACL) that is the DNS whitelist.
   4: If the DNS recursive resolver's IP address IS listed in the ACL,
      then the response to that specific DNS recursive resolver can
      contain both A (IPv4) and AAAA (IPv6) address records.
   5: If the DNS recursive resolver's IP address IS NOT listed in the
      ACL, then the response to that specific DNS recursive resolver
      can contain only A (IPv4) address records and therefore cannot
      contain AAAA (IPv6) address records.

                 Figure 1: DNS Whitelisting - System Logic



































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   ---------------------------------------------------------------------
   A query is sent from a DNS recursive resolver that IS NOT on the DNS
   whitelist:

               Request                        Request
           www.example.com                    www.example.com
                         +-------------+             +-----------------+
     ++--++   ---------> |  RESOLVER   |  ---------> | www.example.com |
     ||  ||              | **IS NOT**  |             | IN A exists     |
   +-++--++-+            |     ON      |             | IN AAAA exists  |
   +--------+            | example.com |             |                 |
      Host    <--------- |  WHITELIST  |  <--------- |                 |
    Computer   A Record  +-------------+  A Record   +-----------------+
               Response   DNS Recursive   Response       example.com
                (IPv4)      Resolver       (IPv4)        Authoritative
                              #1                            Server
   ---------------------------------------------------------------------
   A query is sent from a DNS recursive resolver that IS on the DNS
   whitelist:

               Request                        Request
           www.example.com                    www.example.com
                         +-------------+             +-----------------+
     ++--++   ---------> |  RESOLVER   |  ---------> | www.example.com |
     ||  ||              |   **IS**    |             | IN A exists     |
   +-++--++-+            |     ON      |             | IN AAAA exists  |
   +--------+            | example.com |             |                 |
      Host    <--------- |  WHITELIST  |  <--------- |                 |
    Computer  A and AAAA +-------------+ A and AAAA  +-----------------+
               Record     DNS Recursive   Record        example.com
              Responses     Resolver     Responses      Authoritative
              (IPv4+IPv6)      #2        (IPv4+IPv6)       Server
   ---------------------------------------------------------------------

              Figure 2: DNS Whitelisting - Functional Diagram


3.  Concerns Regarding DNS Whitelisting

   There are a number of potential implications relating to DNS
   whitelisting, which have raised various concerns in some parts of the
   Internet community.  Many of those potential implications are
   described in Section 7.

   Some parties in the Internet community are concerned that this
   emerging practice of DNS whitelisting for IPv6 address records could
   represent a departure from the generally accepted practices regarding
   IPv4 address records in the DNS on the Internet.  These parties



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   explain their belief that for A records, containing IPv4 addresses,
   once an authoritative server operator adds the A record to the DNS,
   then any DNS recursive resolver on the Internet can receive that A
   record in response to a query.  By extension, this means that any of
   the hosts connected to any of these DNS recursive resolvers can
   receive the IPv4 address records for a given FQDN.  This enables new
   server hosts which are connected to the Internet, and for which a
   fully qualified domain name (FQDN) such as www.example.com has been
   added to the DNS with an IPv4 address record, to be almost
   immediately reachable by any host on the Internet.  In this case,
   these new servers hosts become more and more widely accessible as new
   networks and new end user hosts connect to the Internet over time
   [EDITORIAL: consider reference to network effects].  It also means
   that the new server hosts do not need to know about these new
   networks and new end user hosts in order to make their content and
   applications available to them, in essence that each end in this end-
   to-end model is responsible for connecting to the Internet and once
   they have done so they can connect to each other without additional
   impediments or middle networks or intervening networks or servers
   knowing about these end points and whether one is allowed to contact
   the other.

   In contrast, these parties are concerned that DNS whitelisting may
   fundamentally change this model.  As a result, in this altered end-
   to-end model, one end (where the end user is located) cannot readily
   connect to the other end (where the content is located), without
   parts of the middle used by one end being known by the other end and
   approved for access to that end.  Thus, as new networks connect to
   the Internet over time, those networks need to contact any and all
   domains which have implemented DNS whitelisting in order to apply to
   be added to their DNS whitelist, in the hopes of making the content
   and applications residing on named server hosts in those domains
   accessible by the end user hosts on that new network.  Furthermore,
   this same need to contact all domains implementing DNS whitelisting
   also applies to all existing networks connected to the Internet.

   Therefore, these concerned parties explain, whereas in the current
   IPv4 Internet when a new server host is added to the Internet it is
   widely available to all end user hosts and networks, when DNS
   whitelisting of IPv6 records is used then these new server hosts are
   not accessible to any end user hosts or networks until such time as
   the operator of the authoritative DNS servers for those new server
   hosts expressly authorizes access to those new server hosts by adding
   DNS recursive resolvers around the Internet to the ACL.  This could
   represent a significant change in reachability of content and
   applications by end users and networks as these end user hosts and
   networks transition to IPv6.  Therefore, a concern expressed is that
   if much of the content that end users are most interested in is not



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   accessible as a result, then end users and/or networks may resist
   adoption of IPv6 or actively seek alternatives to it, such as using
   multi-layer network address translation (NAT) techniques like NAT444
   [I-D.shirasaki-nat444] on a long-term basis.  There is also concern
   that this practice also could disrupt the continued increase in
   Internet adoption by end users if they cannot simply access new
   content and applications but must instead contact the operator of
   their DNS recursive resolver, such as their ISP or another third
   party, to have their DNS recursive resolver authorized for access to
   the content or applications that interests them.  Meanwhile, these
   parties say, over 99.9% of all other end users that are also using
   that same network or DNS recursive resolver are unable to access the
   IPv6-based content, despite their experience being a positive one.

   [EDITORIAL: Are there additional concerns to add here?]


4.  Similarities to Split DNS

   DNS whitelisting as described herein is in some ways similar to so-
   called split DNS, which is briefly described in Section 3.8 of
   [RFC2775].  When split DNS is used, the authoritative DNS server
   returns different responses depending upon what host has sent the
   query.  While [RFC2775] notes the typical use of split DNS is to
   provide one answer to hosts on an Intranet and a different answer to
   hosts on the Internet, the essence is that different answers are
   provided to hosts on different networks.  This is basically the way
   that DNS whitelisting works, in so far as hosts of different
   networks, which use different DNS recursive resolvers, receive
   different answers if one DNS recursive resolver is on the whitelist
   and the other is not.  Thus, in a way, DNS whitelisting could in some
   ways be considered split DNS on the public Internet, though with some
   differences.

   In [RFC2956], Internet transparency and Internet fragmentation
   concerns regarding split DNS are detailed in Section 2.1.  [RFC2956]
   further notes in Section 2.7, concerns regarding split DNS and that
   it "makes the use of Fully Qualified Domain Names (FQDNs) as endpoint
   identifiers more complex."  Section 3.5 of [RFC2956] further
   recommends that maintaining a stable approach to DNS operations is
   key during transitions such as the one to IPv6 that is underway now,
   stating that "Operational stability of DNS is paramount, especially
   during a transition of the network layer, and both IPv6 and some
   network address translation techniques place a heavier burden on
   DNS."






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5.  Likely Deployment Scenarios

   In considering how DNS whitelisting may emerge more widely, there are
   two likely deployment scenarios, which are explored below.

5.1.  Deploying DNS Whitelisting Universally

   The least likely deployment scenario is one where DNS whitelisting
   becomes a standardized process across all authoritative DNS servers,
   across the entire Internet.  While this scenario is the least likely,
   due to some parties not sharing the concerns that have so far
   motivated the use of DNS whitelisting, it is nonetheless conceivable
   that it could be one of the ways in which DNS whitelisting may be
   deployed.

   In order for this deployment scenario to occur, it is likely that DNS
   whitelisting functionality would need to be built into all
   authoritative DNS server software, and that all operators of
   authoritative DNS servers would have to upgrade their software and
   enable this functionality.  Furthermore, it is likely that new
   Internet Draft documents would need to be developed which describe
   how to properly configure, deploy, and maintain DNS whitelisting.  As
   a result, it is unlikely that DNS whitelisting would, at least in the
   next several years, become universally deployed.  Furthermore, these
   DNS whitelists are likely to vary on a domain-by-domain basis,
   depending upon a variety of factors.  Such factors may include the
   motivation of each domain owner, the location of the DNS recursive
   resolvers in relation to the source content, as well as various other
   parameters that may be transitory in nature, or unique to a specific
   end user host type.  Thus, it is probably unlikely that a single
   clearinghouse for managing whitelisting is possible; it will more
   likely be unique to the source content owners and/or domains which
   implement DNS whitelists.

   While this scenario may be unlikely, it may carry some benefits.
   First, parties performing troubleshooting would not have to determine
   whether or not DNS whitelisting was being used, as it always would be
   in use.  In addition, if universally deployed, it is possible that
   the criteria for being added to or removed from a DNS whitelist could
   be standardized across the entire Internet.  Nevertheless, even if
   uniform DNS whitelisting policies were not standardized, is also
   possible that a central registry of these policies could be developed
   and deployed in order to make it easier to discover them, a key part
   of achieving transparency regarding DNS whitelisting.

   [EDITORIAL: Are there additional benefits or challenges to add here?]





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5.2.  Deploying DNS Whitelisting On An Ad Hoc Basis

   This is the most likely deployment scenario for DNS whitelisting, as
   it seems today, is where some interested parties engage in DNS
   whitelisting but many or most others do not do so.  What can make
   this scenario challenging from the standpoint of a DNS recursive
   resolver operator is determining which domains implement DNS
   whitelisting, particularly since a domain may not do so as they
   initially transition to IPv6, and may instead do so later.  Thus, a
   DNS recursive resolver operator may initially believe that they can
   receive AAAA responses with IPv6 addresses as a domain adopts IPv6,
   but then notices via end user reports that they no longer receive
   AAAA responses due to that site adopting DNS whitelisting.

   Thus, in contrast to universal deployment of DNS whitelisting,
   deployment on an ad hoc basis is likely to be significantly more
   challenging from an operational, monitoring, and troubleshooting
   standpoint.  In this scenario, a DNS recursive resolver operator will
   have no way to systematically determine whether DNS whitelisting is
   or is not implemented for a domain, since the absence of AAAA records
   with IPv6 addresses may simply be indicative that the domain has not
   yet added IPv6 addressing for the domain, not that they have done so
   but have restricted query access via DNS whitelisting.  As a result,
   discovering which domains implement DNS whitelisting, in order to
   differentiate them from those that do not, is likely to be
   challenging.

   On the other hand, one benefit of DNS whitelisting being deployed on
   an ad hoc basis is that only the domains that are interested in doing
   so would have to upgrade their authoritative DNS servers in order to
   implement the ACLs necessary to perform DNS whitelisting.

   [EDITORIAL: Additional benefits or challenges to add?]


6.  What Problems Are DNS Whitelisting Implementers Trying To Solve?

   As noted in Section 1, domains which implement DNS whitelisting are
   attempting to protect a few users of their domain, which happen to
   have impaired IPv6 access, from having a negative end user
   experience.  While it is outside the scope of this document to
   explore the various reasons why a particular user may experience
   impaired IPv6 access, for the users which experience this it is a
   very real effect and would of course affect access to all or most
   IPv4 and IPv6 dual stack servers.  This negative end user experience
   can range from someone slower than usual (as compared to native IPv4-
   based access), to extremely slow, to no access to the domain
   whatsoever.



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   Thus, parties which implement DNS whitelisting are attempting to
   provide a good experience to these end users.  While one can debate
   whether DNS whitelisting is the optimal solution, it is quite clear
   that DNS whitelisting implementers are extremely interested in the
   performance of their services for end users as a primary motivation.

   [EDITORIAL 1: More motivations to add?]

   [EDITORIAL 2:Any good external references to consider adding?]


7.  Implications of DNS Whitelisting

   There are many potential implications of DNS whitelisting.  In the
   sections below, the key potential implications are listed in some
   detail.

7.1.  Architectural Implications

   DNS whitelisting could be perceived as somewhat modifying the end-to-
   end model that prevails on the IPv4 Internet today.  This approach
   moves additional access control information and policies into the
   middle of the network on the IPv6-addressed Internet, which did not
   exist before on the IPv4-addressed Internet.  This could raise some
   risks noted in [RFC3724], which in explaining the history of the end-
   to-end principle [RFC1958] explains that one of the goals is to
   minimize the state, policies, and other functions needed in the
   middle of the network in order to enable end-to-end communications on
   the Internet.

   It is also possible that DNS whitelisting could place at risk some of
   the benefits of the end-to-end principle, as listed in Section 4.1 of
   [RFC3724], such as protection of innovation.  Further, while
   [RFC3234] details issues and concerns regarding so-called
   middleboxes, there may be parallels to DNS whitelisting, especially
   concerning modified DNS servers noted in Section 2.16 of [RFC3234],
   and more general concerns noted in Section 1.2 of [RFC3234] about the
   introduction of new failure modes, that configuration is no longer
   limited to two ends of a session, and that diagnosis of failures and
   misconfigurations is more complex.

   In [Tussle in Cyberspace], the authors note concerns regarding the
   introduction of new control points, as well as "kludges" to the DNS,
   as risks to the goal of network transparency in the end-to-end model.
   Some parties concerned with the emerging use of DNS whitelisting have
   shared similar concerns, which may make [Tussle in Cyberspace] an
   interesting and relevant document.  In addition, [Rethinking the
   design of the Internet] reviews similar issues that may be of



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   interest to readers of this document.

   In order to explore and better understand these high-level
   architectural implications and concerns in more detail, the following
   sections explore more specific potential implications.

7.2.  Public IPv6 Address Reachability Implications

   The predominant experience of end user hosts and servers on the IPv4-
   addressed Internet today is that, very generally speaking, when a new
   server with a public IPv4 address is added, that it is then globally
   accessible by IPv4-addressed hosts.  For the purposes of this
   document, that concept can be considered "pervasive reachability".
   It has so far been assumed that the same expectations of reachability
   would exist in the IPv6-addressed Internet.  However, if DNS
   whitelisting is deployed, this will not be the case since only end
   user hosts using DNS recursive resolvers which have been added to the
   ACL of a given domain using DNS whitelisting would be able to reach
   new servers in that given domain via IPv6 addresses.

   Thus, the expectation of any end user host being able to connect to
   any server (essentially both hosts, just at either end of the
   network), defined here as "pervasive reachability", will change to
   "restricted reachability" with IPv6.

   [EDITORIAL: Additional implications?]

7.3.  Operational Implications

   This section explores some of the operationally related implications
   which may occur as a result of, related to, or necessary when
   engaging in the practice of DNS whitelisting.

7.3.1.  De-Whitelisting May Occur

   If it is possible for a DNS recursive resolver to be added to a
   whitelist, then it is also possible for that resolver to be removed
   from the whitelist, also known as de-whitelisting.  Since de-
   whitelisting can occur, whether through a decision by the
   authoritative server operator or the domain owner, or even due to a
   technical error, an operator of a DNS recursive resolver will have
   new operational and monitoring requirements and/or needs as noted in
   Section 7.3.3, Section 7.3.4, Section 7.3.5, and Section 7.5.

7.3.2.  Authoritative DNS Server Operational Implications

   Operators of authoritative servers may need to maintain an ACL a
   server-wide basis affecting all domains, on a domain-by-domain basis,



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   as well as on a combination of the two.  As a result, operational
   practices and software capabilities may need to be developed in order
   to support such functionality.  In addition, processes may need to be
   put in place to protect against inadvertently adding or removing IP
   addresses, as well as systems and/or processes to respond to such
   incidents if and when they occur.  For example, a system may be
   needed to record DNS whitelisting requests, report on their status
   along a workflow, add IP addresses when whitelisting has been
   approved, remove IP addresses when they have been de-whitelisted, log
   the personnel involved and timing of changes, schedule changes to
   occur in the future, and to roll back any inadvertent changes.

   Such operators may also need implement new forms of monitoring in
   order to apply change control, as noted briefly in Section 7.3.4.

   [EDITORIAL: Additional implications?]

7.3.3.  DNS Recursive Resolver Server Operational Implications

   Operators of DNS recursive resolvers, which may include ISPs,
   enterprises, universities, governments, individual end users, and
   many other parties, are likely to need to implement new forms of
   monitoring, as noted briefly in Section 7.3.4.  But more critically,
   such operators may need to add people, processes, and systems in
   order to manage countless DNS whitelisting applications, for all
   domains that the end users of such servers are interested in now or
   in which they may be interested in the future.  As such anticipation
   of interesting domains is likely infeasible, it is more likely that
   such operators may either choose to only apply to be whitelisted for
   a domain based upon one or more end user requests, or that they will
   attempt to do so for all domains.

   When such operators apply for DNS whitelisting for all domains, that
   may mean doing so for all registered domains.  Thus, some system
   would have to be developed to discover whether each domain has been
   whitelisted or not, which is touched on in Section 5 and may vary
   depending upon whether DNS whitelisting is universally deployed or is
   deployed on an ad hoc basis.

   Furthermore, these operators will need to develop processes and
   systems to track the status of all DNS whitelisting applications,
   respond to requests for additional information related to these
   applications, determine when and if applications have been denied,
   manage appeals, and track any de-whitelisting actions.  Given the
   incredible number of domains in existence, the ease with which a new
   domain can be added, and the continued strong growth in the numbers
   of new domains, readers should not underestimate the potential
   significance in personnel and expense that this could represent for



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   such operators.  In addition, it is likely that systems and personnel
   may also be needed to handle new end user requests for domains for
   which to apply for DNS whitelisting, and/or inquiries into the status
   of a whitelisting application, reports of de-whitelisting incidents,
   general inquiries related to DNS whitelisting, and requests for DNS
   whitelisting-related troubleshooting by these end users.

   [EDITORIAL: Additional implications?]

7.3.4.  Monitoring Implications

   Once a DNS recursive resolver has been whitelisted for a particular
   domain, then the operator of that DNS recursive resolver may need to
   implement monitoring in order to detect the possible loss of
   whitelisting status in the future.  This DNS recursive resolver
   operator could configure a monitor to check for a AAAA response in
   the whitelisted domain, as a check to validate continued status on
   the DNS whitelist.  The monitor could then trigger an alert if at
   some point the AAAA responses were no longer received, so that
   operations personnel could begin troubleshooting, as outlined in
   Section 7.3.5.

   Also, authoritative DNS server operators are likely to need to
   implement new forms of monitoring.  In this case, they may desire to
   monitor for significant changes in the size of the whitelist within a
   certain period of time, which might be indicative of a technical
   error such as the entire ACL being removed.  These operators may also
   wish to monitor their workflow process for reviewing and acting upon
   DNS whitelisting applications and appeals, potentially measuring and
   reporting on service level commitments regarding the time an
   application or appeal can remain at each step of the process,
   regardless of whether or not such information is shared with parties
   other than that authoritative DNS server operator.

   These are but a few examples of the types of monitoring that may be
   called for as a result of DNS whitelisting, among what are likely
   many other types and variations.

   [EDITORIAL: Additional implications?]

7.3.5.  Troubleshooting Implications

   The implications of DNS whitelisted present many challenges, which
   have been detailed in Section 7.  These challenges may negatively
   affect the end users' ability to troubleshoot, as well as that of DNS
   recursive resolver operators, ISPs, content providers, domain owners
   (where they may be different from the operator of the authoritative
   DNS server for their domain), and other third parties.  This may make



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   the process of determining why a server is not reachable
   significantly more complex.

   [SECTION INCOMPLETE - MIGHT LIKE TO ADD SOME EXAMPLES HERE]

   [EDITORIAL: Additional implications?]

7.3.6.  Additional Implications If Deployed On An Ad Hoc Basis

   [SECTION INCOMPLETE - IS THIS NEEDED? - PLACEHOLDER FOR NOW]

   [EDITORIAL: Additional implications?]

7.4.  Homogeneity May Be Encouraged

   A broad trend which has existed on the Internet appears to be a move
   towards increasing levels of heterogeneity.  One manifestation of
   this is in an increasing number, variety, and customization of end
   user hosts, including home network, operating systems, client
   software, home network devices, and personal computing devices.  This
   trend appears to have had a positive effect on the development and
   growth of the Internet.  A key facet of this that has evolved is the
   ability of the end user to connect any technically compliant device
   or use any technically compatible software to connect to the
   Internet.  Not only does this trend towards greater heterogeneity
   reduce the control which is exerted in the middle of the network,
   described in positive terms in [Tussle in Cyberspace], [Rethinking
   the design of the Internet], and [RFC3724], but it can also help to
   enable greater and more rapid innovation at the edges.

   An unfortunate implication of the adoption of DNS whitelisting may be
   the encouragement of a reversal of this trend, which would be a move
   back towards greater levels of homogeneity.  In this case, a domain
   owner which has implemented DNS whitelisting may prefer greater
   levels of control be exerted over end user hosts (which broadly
   includes all types of end user software and hardware) in order to
   attempt to enforce technical standards relating to establishing
   certain IPv6 capabilities or the enforcing the elimination of or
   restriction of certain end user hosts.  While the domain operator is
   attempting to protect, maintain, and/or optimize the end user
   experience for their domain, the collective result of many domains
   implementing DNS whitelisting, or even a few important domains
   implementing DNS whitelisting, may be to encourage a return to more
   homogenous and/or controlled end user hosts.  Unfortunately, this
   could have unintended side effects on and counter-productive
   implications for future innovation at the edges of the network.





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7.5.  Technology Policy Implications

   A key technology policy implication concerns the policies relating to
   the process of reviewing an application for DNS whitelisting, and the
   decision-making process regarding whitelisting for a domain.
   Important questions may include whether these policies have been
   fully and transparently disclosed, are non-discriminatory, and are
   not anti-competitive.  A related implication is whether and what the
   process for appeals is, when a domain decides not to add a DNS
   recursive resolver to the whitelist.  Key questions here may include
   whether appeals are allowed, what the process is, what the expected
   turn around time is, and whether the appeal will be handled by an
   independent third party or other entity/group.

   A further implications arises when de-whitelisting occurs.  Questions
   that may naturally be raised in such a case include whether the
   criteria for de-whitelisting have been fully and transparently
   disclosed, are non-discriminatory, and are not anti-competitive.
   Additionally, the question of whether or not there was a cure period
   available prior to de-whitelisting, during which troubleshooting
   activities, complaint response work, and corrective actions may be
   attempted, and whether this cure period was a reasonable amount of
   time.

   It is also conceivable that whitelisting and de-whitelisting
   decisions could be quite sensitive to concerned parties beyond the
   operator of the domain which has implemented DNS whitelisting and the
   operator of the DNS recursive resolver, including end users,
   application developers, content providers, advertisers, public policy
   groups, governments, and other entities, which may also seek to
   become involved in or express opinions concerning whitelisting and/or
   de-whitelisting decisions.  Lastly, it is conceivable that any of
   these interested parties or other related stakeholders may seek
   redress outside of the process a domain has establishing for DNS
   whitelisting and de-whitelisting.

   A final concern is that decisions relating to whitelisting and de-
   whitelisting may occur as an expression of other commercial,
   governmental, and/or cultural conflicts, given the new control point
   which has be established with DNS whitelisting.  For example, in one
   imagined scenario, it may be conceivable that one government is
   unhappy with a news story or book published in a particular country,
   and that this government may retaliate against or protest this news
   story or book by requiring domains operating within that government's
   territory to de-whitelist commercial, governmental, or other entities
   involved in or related to (however tangentially) publishing the news
   story or book.  By the same token, a news site operating in multiple
   territories may be unhappy with governmental policies in one



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   particular territory and may choose to express dissatisfaction in
   that territory by de-whitelisting commercial, governmental, or other
   entities in that territory.  Thus, it seems possible that DNS
   whitelisting and de-whitelisting could become a vehicle for
   adjudicating other disputes, and that this may well have intended and
   unintended consequences for end users which are affected by such
   decisions and are unlikely to be able to express a strong voice in
   such decisions.

7.6.  IPv6 Adoption Implications

   As noted in Section 3, the implications of DNS whitelisting may drive
   end users and/or networks to delay, postpone, or cancel adoption of
   IPv6, or to actively seek alternatives to it.  Such alternatives may
   include the use of multi-layer network address translation (NAT)
   techniques like NAT444 [I-D.shirasaki-nat444], which these parties
   may decide to pursue on a long-term basis to avoid the perceived
   costs and aggravations related to DNS whitelisting.  This could of
   course come at the very time that the Internet community is trying to
   get these very same parties interested in IPv6 and motivated to begin
   the transition to IPv6.  As a result, parties concerned over the
   negative implications of DNS whitelisting have said they are very
   concerned of the negative effects that this practice could have on
   the adoption of IPv6 if it became widespread or was adopted by key
   parties in the Internet ecosystem.

   [EDITORIAL: Additional implications?]


8.  Solutions

8.1.  Implement DNS Whitelisting Universally

   One obvious solution is to implement DNS whitelisted universally, and
   to do so using some sort of centralized registry of DNS whitelisting
   policies, contracts, processes, or other information.  This potential
   solution seems unlikely at the current time.

   [EDITORIAL: More to add?]

8.2.  Implement DNS Whitelisting On An Ad Hoc Basis

   If DNS whitelisting was to be adopted more widely, it is likely to be
   adopted on this ad hoc, or domain-by-domain basis.  Therefore, only
   those domains interested in DNS whitelisting would need to adopt the
   practice, though as noted herein discovering that they a given domain
   has done so may be problematic.




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   [EDITORIAL: More to add?]

8.3.  Do Not Implement DNS Whitelisting

   As an alternative to adopting DNS whitelisting, the Internet
   community can instead choose to take no action whatsoever,
   perpetuating the current predominant authoritative DNS operational
   model on the Internet, and leave it up to end users with IPv6-related
   impairments to discover and fix those impairments.

8.3.1.  Solving Current End User IPv6 Impairments

   A further extension of not implementing DNS whitelisting, is to also
   endeavor to actually fix the underlying technical problems that have
   prompted the consideration of DNS whitelisting in the first place, as
   an alternative to trying to apply temporary workarounds to avoid the
   symptoms of underlying end user IPv6 impairments.  A first step is
   obviously to identify which users have such impairments, which would
   appear to be possible, and then to communicate this information to
   end users.  Such end user communication is likely to be most helpful
   if the end user is not only alerted to a potential problem but is
   given careful and detailed advice on how to resolve this on their
   own, or where they can seek help in doing so.

   One challenge with this option is the potential difficulty of
   motivating members of the Internet community to work collectively
   towards this goal, sharing the labor, time, and costs related to such
   an effort.  Of course, since just such a community effort is now
   underway for IPv6, it is possible that this would call for only a
   moderate amount of additional work.

   [EDITORIAL: More to add?]


9.  Security Considerations

   There are no particular security considerations if DNS whitelisting
   is not adopted, as this is how the public Internet works today with A
   records.

   However, if DNS whitelisting is adopted, organizations which apply
   DNS whitelisting policies in their authoritative servers should have
   procedures and systems which do not allow unauthorized parties to
   either remove whitelisted DNS resolvers from the whitelist or add
   non-whitelisted DNS resolvers to the whitelist.  Should such
   unauthorized additions or removals from the whitelist can be quite
   damaging, and result in content providers and/or ISPs to incur
   substantial support costs resulting from end user and/or customer



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   contacts.  As such, great care must be taken to control access to the
   whitelist for an authoritative server.

   In addition, two other key security-related issues should be taken
   into consideration:

9.1.  DNSSEC Considerations

   DNS security extensions defined in [RFC4033], [RFC4034], and
   [RFC4035] use cryptographic digital signatures to provide origin
   authentication and integrity assurance for DNS data.  This is done by
   creating signatures for DNS data on a Security-Aware Authoritative
   Name Server that can be used by Security-Aware Resolvers to verify
   the answers.  Since DNS whitelisting is implemented on an
   authoritative server, which provides different answers depending upon
   which resolver server has sent a query, the DNSSEC chain of trust is
   not altered.  Therefore there are no DNSSEC implications per se, and
   thus no specific DNSSEC considerations to be listed.

9.2.  Authoritative DNS Response Consistency Considerations

   [INCOMPLETE!!]

   While Section 9.1 does not contain any specific DNSSEC
   considerations.  However, it is certainly conceivable that security
   concerns may arise when end users or other parties notice that the
   responses sent from an authoritative DNS server appear to vary from
   one network or one DNS recursive resolver to another.  This may give
   rise to concerns that, since the authoritative responses vary that
   there is some sort of security issue and/or some or none of the
   responses can be trusted.


10.  IANA Considerations

   There are no IANA considerations in this document.


11.  Contributors

   The following people made significant textual contributions to this
   document and/or played an important role in the development and
   evolution of this document:

   John Brzozowski

   Chris Griffiths




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   Tom Klieber

   Yiu Lee

   Rich Woundy


12.  Acknowledgements

   The authors and contributors also wish to acknowledge the assistance
   of the following individuals in helping us to develop and/or review
   this document:


13.  References

13.1.  Normative References

   [RFC1035]  Mockapetris, P., "Domain names - implementation and
              specification", STD 13, RFC 1035, November 1987.

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

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

   [RFC2956]  Kaat, M., "Overview of 1999 IAB Network Layer Workshop",
              RFC 2956, October 2000.

   [RFC3234]  Carpenter, B. and S. Brim, "Middleboxes: Taxonomy and
              Issues", RFC 3234, February 2002.

   [RFC3724]  Kempf, J., Austein, R., 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.

   [RFC4033]  Arends, R., Austein, R., Larson, M., Massey, D., and S.
              Rose, "DNS Security Introduction and Requirements",
              RFC 4033, March 2005.

   [RFC4034]  Arends, R., Austein, R., Larson, M., Massey, D., and S.
              Rose, "Resource Records for the DNS Security Extensions",
              RFC 4034, March 2005.

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



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13.2.  Informative References

   [I-D.shirasaki-nat444]
              Yamagata, I., Shirasaki, Y., Nakagawa, A., Yamaguchi, J.,
              and H. Ashida, "NAT444", draft-shirasaki-nat444-02 (work
              in progress), July 2010.

   [IETF 77 DNSOP WG Presentation]
              Gashinsky, I., "IPv6 & recursive resolvers: How do we make
              the transition less painful?", IETF 77 DNS Operations
              Working Group, March 2010,
              <http://www.ietf.org/proceedings/77/slides/dnsop-7.pdf>.

   [Network World Article on DNS Whitelisting]
              Marsan, C., "Google, Microsoft, Netflix in talks to create
              shared list of IPv6 users", Network World , March 2010, <h
              ttp://www.networkworld.com/news/2010/
              032610-dns-ipv6-whitelist.html>.

   [Network World Article on IETF 77 DNSOP WG Presentation]
              Marsan, C., "Yahoo proposes 'really ugly hack' to DNS",
              Network World , March 2010, <http://www.networkworld.com/
              news/2010/032610-yahoo-dns.html>.

   [Rethinking the design of the Internet]
              Blumenthal, M. and D. Clark, "Rethinking the design of the
              Internet: The end to end arguments vs. the brave new
              world", ACM Transactions on Internet Technology Volume 1,
              Number 1, Pages 70-109, August 2001, <http://
              dspace.mit.edu/bitstream/handle/1721.1/1519/
              TPRC_Clark_Blumenthal.pdf>.

   [Tussle in Cyberspace]
              Braden, R., Clark, D., Sollins, K., and J. Wroclawski,
              "Tussle in Cyberspace: Defining Tomorrow's Internet",
              Proceedings of ACM Sigcomm 2002, August 2002, <http://
              groups.csail.mit.edu/ana/Publications/PubPDFs/
              Tussle2002.pdf>.


Appendix A.  Document Change Log

   [RFC Editor: This section is to be removed before publication]

   -00: First version published

   -01: Updated the title of the document, to avoid confusion (based on
   feedback)



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Appendix B.  Open Issues

   [RFC Editor: This section is to be removed before publication]

   1.   Incorporate any feedback received at IETF 79

   2.   Incorporate feedback from Erik Kline, received 10/1/2010

   3.   Incorporate feedback from Brian Carpenter, received 10/19/2010

   4.   Bring on new contributors: Hannes Tschofenig and Danny McPherson
        has so far offered to contribute.

   5.   Close out any EDITORIAL notes

   6.   Add any good references throughout the document

   7.   Add reviewers to the acknowledgements section

   8.   Ensure references are in the proper section (normative/
        informative)

   9.   Include a number of references from RFC3724?

   10.  Call DNS WL something else or add note to the effect that this
        is unrelated to DNS WL used for email - such as www.dnswl.org


Author's Address

   Jason Livingood
   Comcast Cable Communications
   One Comcast Center
   1701 John F. Kennedy Boulevard
   Philadelphia, PA  19103
   US

   Email: jason_livingood@cable.comcast.com
   URI:   http://www.comcast.com












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