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Versions: (draft-livingood-dns-whitelisting-implications) 00 01 02 03 04 05 06 07 08 09 10 11 RFC 6589

IPv6 Operations                                             J. Livingood
Internet-Draft                                                   Comcast
Intended status: Informational                         February 22, 2011
Expires: August 26, 2011


                IPv6 AAAA DNS Whitelisting Implications
         draft-ietf-v6ops-v6-aaaa-whitelisting-implications-03

Abstract

   The objective of this document is to describe what the whitelisting
   of DNS AAAA resource records is, hereafter referred to as DNS
   whitelisting, as well as the implications of this emerging practice
   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
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

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

   This Internet-Draft will expire on August 26, 2011.

Copyright Notice

   Copyright (c) 2011 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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



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   described in the Simplified BSD License.


















































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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  5
   2.  How DNS Whitelisting Works . . . . . . . . . . . . . . . . . .  6
     2.1.  Description of the Operation of DNS Whitelisting . . . . .  7
   3.  What Problems Are Implementers Trying To Solve?  . . . . . . .  8
   4.  Concerns Regarding DNS Whitelisting  . . . . . . . . . . . . .  9
   5.  Similarities to Other DNS Operations . . . . . . . . . . . . . 12
     5.1.  Similarities to Split DNS  . . . . . . . . . . . . . . . . 12
     5.2.  Similarities to DNS Load Balancing . . . . . . . . . . . . 12
   6.  Likely Deployment Scenarios  . . . . . . . . . . . . . . . . . 13
     6.1.  Deploying DNS Whitelisting On An Ad Hoc Basis  . . . . . . 13
     6.2.  Deploying DNS Whitelisting Universally . . . . . . . . . . 14
   7.  Implications of DNS Whitelisting . . . . . . . . . . . . . . . 15
     7.1.  Architectural Implications . . . . . . . . . . . . . . . . 15
     7.2.  Public IPv6 Address Reachability Implications  . . . . . . 16
     7.3.  Operational Implications . . . . . . . . . . . . . . . . . 17
       7.3.1.  De-Whitelisting May Occur  . . . . . . . . . . . . . . 17
       7.3.2.  Authoritative DNS Server Operational Implications  . . 17
       7.3.3.  DNS Recursive Resolver Server Operational
               Implications . . . . . . . . . . . . . . . . . . . . . 18
       7.3.4.  Monitoring Implications  . . . . . . . . . . . . . . . 19
       7.3.5.  Implications of Operational Momentum . . . . . . . . . 19
       7.3.6.  Troubleshooting Implications . . . . . . . . . . . . . 20
       7.3.7.  Additional Implications If Deployed On An Ad Hoc
               Basis  . . . . . . . . . . . . . . . . . . . . . . . . 20
     7.4.  Homogeneity May Be Encouraged  . . . . . . . . . . . . . . 20
     7.5.  Technology Policy Implications . . . . . . . . . . . . . . 21
     7.6.  IPv6 Adoption Implications . . . . . . . . . . . . . . . . 22
   8.  Solutions  . . . . . . . . . . . . . . . . . . . . . . . . . . 23
     8.1.  Implement DNS Whitelisting Universally . . . . . . . . . . 23
     8.2.  Implement DNS Whitelisting On An Ad Hoc Basis  . . . . . . 23
     8.3.  Do Not Implement DNS Whitelisting  . . . . . . . . . . . . 23
       8.3.1.  Solving Current End User IPv6 Impairments  . . . . . . 24
       8.3.2.  Gain Experience Using IPv6 Transition Names  . . . . . 24
   9.  Is DNS Whitelisting a Recommended Practice?  . . . . . . . . . 24
   10. Security Considerations  . . . . . . . . . . . . . . . . . . . 25
     10.1. DNSSEC Considerations  . . . . . . . . . . . . . . . . . . 25
     10.2. Authoritative DNS Response Consistency Considerations  . . 26
   11. Privacy Considerations . . . . . . . . . . . . . . . . . . . . 26
   12. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 27
   13. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 27
   14. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 27
   15. References . . . . . . . . . . . . . . . . . . . . . . . . . . 28
     15.1. Normative References . . . . . . . . . . . . . . . . . . . 28
     15.2. Informative References . . . . . . . . . . . . . . . . . . 29
   Appendix A.  Document Change Log . . . . . . . . . . . . . . . . . 31
   Appendix B.  Open Issues . . . . . . . . . . . . . . . . . . . . . 32



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   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 32


















































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1.  Introduction

   This document describes the emerging practice of whitelisting of DNS
   AAAA resource records (RRs), which contain IPv6 addresses, hereafter
   referred to as DNS whitelisting.  The document 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 (sometimes described herein as "highly-
   trafficked domains" or "major domains").  These web site operators,
   or domain operators, observed that when they added AAAA resource
   records to their authoritative DNS servers in order to support IPv6
   access to their content that a small fraction of end users had slow
   or otherwise impaired access to a given web site with both AAAA and A
   resource records.  The fraction of users with such impaired access
   has been estimated to be roughly 0.078% of total Internet users
   [IETF-77-DNSOP] [NW-Article-DNSOP] [Evaluating IPv6 Adoption] [IPv6
   Brokenness].  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 major domains have either implemented DNS whitelisting or are
   considering doing so [NW-Article-DNS-WL] [IPv6 Whitelist Operations].
   When implemented, DNS whitelisting in practice means that a domain's
   authoritative DNS will return a AAAA resource record to DNS recursive
   resolvers [RFC1035] on the whitelist, while returning no AAAA
   resource records to DNS resolvers which are not on the whitelist.  It
   is important to note that these major domains are motivated by a
   desire to maintain a high-quality user experience for all of their
   users.  By engaging in DNS whitelisting, they are attempting to
   shield users with impaired access from the symptoms of those
   impairments.

   Critics of the practice of DNS whitelisting have articulated several
   concerns.  Among these are that:

   o  DNS whitelisting is a very different behavior from the current
      practice concerning the publishing of IPv4 address resource
      records,

   o  that it may create a two-tiered Internet,

   o  that policies concerning whitelisting and de-whitelisting are
      opaque,





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   o  that DNS whitelisting reduces interest in the deployment of IPv6,

   o  that new operational and management burdens are created,

   o  and that the costs and negative implications of DNS whitelisting
      outweigh the perceived benefits, compared to fixing underlying
      impairments.

   This document explores the reasons and motivations for DNS
   whitelisting.  It also explores the outlined concerns regarding this
   practice.  Readers will hopefully better understand what DNS
   whitelisting is, why some parties are implementing it, and what
   criticisms of the practice exist.


2.  How DNS Whitelisting Works

   DNS whitelisting is implemented in authoritative DNS servers.  These
   servers implement IP address-based restrictions on AAAA query
   responses.  So far, DNS whitelisting has been primarily implemented
   by web server operators deploying IPv6-enabled services.  For a given
   operator of a website, such as www.example.com, the operator
   essentially applies an access control list (ACL) on the authoritative
   DNS servers for the domain example.com.  The ACL is populated with
   the IPv4 and/or IPv6 addresses or prefix ranges of DNS recursive
   resolvers on the Internet, which have been authorized to receive AAAA
   resource record responses.  These DNS recursive resolvers are
   operated by third parties, such as ISPs, universities, governments,
   businesses, and individual end users.  If a DNS recursive resolver IS
   NOT matched in the ACL, then AAAA resource records will NOT be sent
   in response to a query for a hostname in the example.com domain.
   However, if a DNS recursive resolver IS matched in the ACL, then AAAA
   resource records will be sent in response to a query for a given
   hostname in the example.com domain.  While these are not network-
   layer access controls they are nonetheless access controls that are a
   factor for end users and other parties like network operators,
   especially as networks and hosts transition from one network address
   family to another (IPv4 to IPv6).

   In practice, DNS whitelisting generally means that a very small
   fraction of the DNS recursive resolvers on the Internet (those in the
   whitelist ACL) will receive AAAA responses.  The large majority of
   DNS resolvers on the Internet will therefore receive only A resource
   records containing IPv4 addresses.  Thus, quite simply, the
   authoritative server hands out different answers depending upon who
   is asking; with IPv4 and IPv6 resource records for some on the
   authorized whitelist, and only IPv4 resource records for everyone
   else.  See Section 2.1 and Figure 1 for a description of how this



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   works.

   Finally, DNS whitelisting can be deployed in two primary ways:
   universally on a global basis, or on an ad hoc basis.  Deployment on
   a universal deployment basis means that DNS whitelisting is
   implemented on all authoritative DNS servers, across the entire
   Internet.  In contrast, deployment on an ad hoc basis means that only
   some authoritative DNS servers, and perhaps even only a few,
   implement DNS whitelisting.  These two potential deployment models
   are described in Section 6.

2.1.  Description of the Operation of DNS Whitelisting

   The system logic of DNS whitelisting is as follows:

   1.  The authoritative DNS server for example.com receives DNS queries
       for the A (IPv4) and AAAA (IPv6) address resource records for the
       FQDN www.example.com, for which AAAA (IPv6) resource records
       exist.

   2.  The authoritative DNS server examines the IP address of the DNS
       recursive resolver sending the AAAA (IPv6) 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 matched in the ACL,
       then the response to that specific DNS recursive resolver can
       contain AAAA (IPv6) address resource records.

   5.  If the DNS recursive resolver's IP address IS NOT matched in the
       ACL, then the response to that specific DNS recursive resolver
       cannot contain AAAA (IPv6) address resource records.  In this
       case, the server should return a response with the response code
       (RCODE) being set to 0 (No Error) with an empty answer section
       for the AAAA record query.















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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
                 AAAA    +-------------+     AAAA    +-----------------+
     ++--++   ---------> |  RESOLVER   |  ---------> | www.example.com |
     ||  ||       A      | **IS NOT**  |      A      | IN A exists     |
   +-++--++-+ ---------> |     ON      |  ---------> | IN AAAA exists  |
   +--------+     A      | example.com |      A      |                 |
      Host    <--------- |  WHITELIST  |  <--------- |                 |
    Computer   A Record  +-------------+  A Record   +-----------------+
               Response   DNS Recursive   Response       example.com
              (only IPv4)   Resolver     (only 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
                AAAA     +-------------+     AAAA    +-----------------+
     ++--++   ---------> |  RESOLVER   |  ---------> | www.example.com |
     ||  ||       A      |   **IS**    |      A      | IN A exists     |
   +-++--++-+ ---------> |     ON      |  ---------> | IN AAAA exists  |
   +--------+   AAAA     | example.com |     AAAA    |                 |
      Host    <--------- |  WHITELIST  |  <--------- |                 |
    Computer      A      |             |      A      |                 |
              <--------- |             |  <--------- |                 |
              A and AAAA +-------------+ A and AAAA  +-----------------+
               Record     DNS Recursive   Record        example.com
              Responses     Resolver     Responses      Authoritative
              (IPv4+IPv6)      #2        (IPv4+IPv6)       Server
   ---------------------------------------------------------------------

              Figure 1: DNS Whitelisting - Functional Diagram


3.  What Problems Are Implementers Trying To Solve?

   As noted in Section 1, domains which implement DNS whitelisting are
   attempting to protect a few users of their domain, who have impaired
   IPv6 access, from having a negative experience (poor performance).
   While it is outside the scope of this document to explore the various
   reasons why a particular user's system (host) may have impaired IPv6
   access, for the users who experience this impairment it is a very
   real performance impact.  It would affect access to all or most dual



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   stack services to which the user attempts to connect.  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.

   While one can debate whether DNS whitelisting is the optimal solution
   to the end user experience problem, it is quite clear that DNS
   whitelisting implementers are interested in maximizing the
   performance of their services for end users as a primary motivation
   for implementation.

   At least one highly-trafficked domain has noted that they have
   received requests to not send DNS responses with AAAA resource
   records to particular resolvers.  In this case, the operators of
   those recursive resolvers have expressed a concern that their IPv6
   network infrastructure is not yet ready to handle the large traffic
   volume which may be associated with the hosts in their network
   connecting to the websites of these domains.  This concern is clearly
   a temporary consideration relating to the deployment of IPv6 network
   infrastructure on the part of networks with end user hosts, rather
   than a long-term concern.  These end user networks may also have
   other tools at their disposal in order to address this concern,
   including applying rules to network equipment such as routers and
   firewalls (this will necessarily vary by the type of network, as well
   as the technologies used and the design of a given network), as well
   as configuration of their recursive resolvers (though modifying or
   suppressing AAAA resource records in a DNSSEC-signed domain on a
   Security-Aware Resolver will be problematic Section 10.1).

   Some implementers with highly-trafficked domains have explained that
   DNS whitelisting is a necessary, though temporary, risk reduction
   tactic intended to ease their transition to IPv6 and minimize any
   perceived risk in such a transition.  As a result, they perceive this
   as a tactic to enable them to incrementally enable IPv6 connectivity
   to their domains during the early phases of their transition to IPv6.

   Finally, some domains, have run IPv6 experiments whereby they added
   AAAA resource records and observed and measured errors [Heise Online
   Experiment], which should be important reading for any domain
   contemplating either the use of DNS whitelisting or simply adding
   IPv6 addressing to their site.


4.  Concerns Regarding DNS Whitelisting

   There are a number of potential implications relating to DNS
   whitelisting, which have been raised as concerns by some parts of the
   Internet community.  Many of those potential implications are further



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   enumerated here and in Section 7.

   Some parties in the Internet community, including ISPs, are concerned
   that the practice of DNS whitelisting for IPv6 address resource
   records represents a departure from the generally accepted practices
   regarding IPv4 address resource records in the DNS on the Internet
   [Whitelisting Concerns].  These parties explain their belief that for
   A resource 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
   resource 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, capitalizing on and
   increasing so-called "network effects" (also called network
   externalities).  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, the concern is that DNS whitelisting may fundamentally
   change this model.  In the altered DNS whitelisting 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
   (recursive resolvers) used by one end (the client, or end user hosts)
   being known to an intermediary (authoritative nameservers) and
   approved for access to the resource at the end.  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 pre-existing (but not whitelisted)
   networks connected to the Internet.

   In the current IPv4 Internet when a new server host is added to the
   Internet it is generally widely available to all end user hosts and
   networks, when DNS whitelisting of IPv6 resource records is used,



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   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 has the potential to be a significant
   change in reachability of content and applications by end users and
   networks as these end user hosts and networks transition to IPv6,
   resulting in more (but different) breakage.  A concern expressed is
   that if much of the content that end users are most interested in is
   not 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 the 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.

   While in Section 1 the level of IPv6-related impairment has been
   estimated to be as high as 0.078% of Internet users, which is a
   primary motivation cited for the practice of DNS whitelisting, it is
   not clear if the level of IPv4-related impairment is more or less
   that this percentage (which in any case is likely to have declined
   since its original citation).  Indeed, as at least one document
   reviewer has pointed out, it may simply be that websites are only
   measuring IPv6 impairments and not IPv4 impairments, whether because
   IPv6 is new or whether those websites are simply unable to or are
   otherwise not in a position to be able to measure IPv4 impairment
   (since this could result in no Internet access whatsoever).  As a
   result, it is worth considering that IPv4-related impairment could
   exceed that of IPv6-related impairment and that such IPv4-related
   impairment may have simply been accepted as "background noise" on the
   Internet for a variety of reasons.  Of course, this comparison of the
   level of worldwide IPv6 impairments to IPv4 impairments is
   speculation, as the author is not aware of any good measurement of
   IPv4-related impairments which are comparable in nature to the IPv6-
   related impairment measurements which have recently been conducted
   around the world.

   An additional concern is that the IP address of a recursive resolver
   is not a precise indicator of the IPv6 preparedness, or lack of IPv6-
   related impairments, of end user hosts which query (use) a particular
   recursive resolver.  While the recursive resolver may be an imperfect



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   proxy for judging IPv6 preparedness, it is at least one of the best
   available methods at the current time.


5.  Similarities to Other DNS Operations

   Some aspects of DNS whitelisting may be considered similar to other
   common DNS operational techniques which are explored below.

5.1.  Similarities to Split DNS

   DNS whitelisting has some similarities to so-called split DNS,
   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,
   whereby hosts on 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.

   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."

5.2.  Similarities to DNS Load Balancing

   DNS whitelisting also has some similarities to DNS load balancing.
   There are of course many ways that DNS load balancing can be
   performed.  In one example, multiple IP address resource records (A
   and/or AAAA) can be added to the DNS for a given FQDN.  This approach
   is referred to as DNS round robin [RFC1794].  DNS round robin may
   also be employed where SRV resource records are used [RFC2782].

   In another example, one or more of the IP address resource records in
   the DNS will direct traffic to a load balancer.  That load balancer,
   in turn, may be application-aware, and pass the traffic on to one or
   more hosts connected to the load balancer which have different IP



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   addresses.  In cases where private IPv4 addresses are used [RFC1918],
   as well as when public IP addresses are used, those end hosts may not
   be directly reachable without passing through the load balancer first
   .  As such, while the IP address resource records have been added to
   the DNS, the end hosts are not necessarily directly reachable, which
   is in a small way similar to one aspect of DNS whitelisting.

   Additionally, a geographically-aware authoritative DNS server may be
   used, as is common with Content Delivery Networks (CDNs) or Global
   Load Balancing (GLB, also referred to as Global Server Load
   Balancing, or GSLB), whereby the IP address resource records returned
   to a resolver in response to a query will vary based on the estimated
   geographic location of the resolver [Resolvers in the Wild].  CDNs
   perform this function in order to attempt to direct hosts to connect
   to the nearest content cache.  As a result, one can see some
   similarities with DNS whitelisting insofar as different IP address
   resource records are selectively returned to resolvers based on the
   IP address of each resolver (or other imputed factors related to that
   IP address).  However, what is different is that in this case the
   resolvers are not deliberately blocked from receiving DNS responses
   containing an entire class of addresses; this load balancing function
   strives to perform a content location-improvement function and not an
   access control function.


6.  Likely Deployment Scenarios

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

   In either of these deployment scenarios, it is possible that
   reputable third parties could create and maintain DNS whitelists, in
   much the same way that blacklists are used for reducing email spam.
   In the email context, a mail operator subscribes to one or more of
   these lists and as such the operational processes for additions and
   deletions to the list are managed by a third party.  A similar model
   could emerge for DNS whitelisting, whether deployment occurs
   universally or on an ad hoc basis.

6.1.  Deploying DNS Whitelisting On An Ad Hoc Basis

   The seemingly most likely deployment scenario is where some
   authoritative DNS server operators implement 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



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   may initially believe that they can receive AAAA responses as a
   domain adopts IPv6, but then notice via end user reports that they no
   longer receive AAAA responses due to that domain adopting DNS
   whitelisting.  Of course, a domain's IPv6 transition may be
   effectively invisible to recursive server operators due to the effect
   of DNS whitelisting.

   In contrast to a universal deployment of DNS whitelisting
   Section 6.2, 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 resource records may simply be indicative that
   the domain has not yet added IPv6 addressing for the domain, rather
   than 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.

   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.

   In this potential deployment scenario, it is also possible that a
   given domain will implement DNS whitelisting temporarily.  A domain,
   particularly a highly-trafficked domain, may choose to do so in order
   to ease their transition to IPv6 through a selective deployment and
   minimize any perceived risk in such a transition.

6.2.  Deploying DNS Whitelisting Universally

   The least likely deployment scenario is one where DNS whitelisting is
   implemented on all authoritative DNS servers, across the entire
   Internet.  While this scenario seems less likely than ad hoc
   deployment 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 is 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.  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



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   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.  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.


7.  Implications of DNS Whitelisting

   There are many potential implications of DNS whitelisting.  The key
   potential implications are detailed below.

7.1.  Architectural Implications

   DNS whitelisting could be perceived as modifying the end-to-end model
   and/or the general notion of the architecture that prevails on the
   Internet today.  This is because this approach moves additional
   access control information and policies into the middle of the DNS
   resolution path of the IPv6-addressed Internet, which generally did
   not exist before on the IPv4-addressed Internet.  This poses some
   risks noted in [RFC3724].  In explaining the history of the end-to-
   end principle [RFC1958] states 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.
   In this case, the middle network should be understood to mean
   anything other than the end hosts involved in communicating with one
   another.  Some state, policies, and other functions have always been
   necessary to enable such end-to-end communication, but the goal of
   the approach has been to minimize this to the greatest extent
   possible.




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

   Two additional sources worth considering as far as implications for
   the end-to-end model are concerned are [Tussle in Cyberspace] and
   [Rethinking the Internet].  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 Internet] reviews similar
   issues that may be of interest to readers of this document.

   Also, it is possible that DNS whitelisting could affect some of the
   architectural assumptions which underlie parts of Section 2 of
   [RFC4213] which outlines the dual stack approach to the IPv6
   transition.  DNS whitelisting could modify the behavior of the DNS,
   as described in Section 2.2 of [RFC4213] and could require different
   sets of DNS servers to be used for hosts that are (using terms from
   that document) IPv6/IPv4 nodes, IPv4-only nodes, and IPv6-only nodes.
   As such, broad use of DNS whitelisting may necessitate the review
   and/or revision of standards documents which describe dual-stack and
   IPv6 operating modes, dual-stack architecture generally, and IPv6
   transition methods, including but not limited to [RFC4213].

7.2.  Public IPv6 Address Reachability Implications

   The predominant experience of end user hosts and servers on the IPv4-
   addressed Internet today is that when a new server with a public IPv4
   address is added to the DNS, that it is then globally accessible by
   IPv4-addressed hosts.  This is a generalization and in Section 5
   there are examples of common cases where this may not necessarily be
   the case.  For the purposes of this argument, that concept of
   accessibility can be considered "pervasive reachability".  It has so
   far been assumed that the same expectations of pervasive 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 are included in the



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   ACL of a given domain using DNS whitelisting would be able to reach
   new servers in that given domain via IPv6 addresses.  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.

   Establishing DNS whitelisting as an accepted practice in the early
   phases of mass IPv6 deployment could well establish it as an integral
   part of how IPv6 DNS resource records are deployed globally.  As a
   result, it is then possible that DNS whitelisting could live on for
   decades on the Internet as a key foundational element of domain name
   management that we will all live with for a long time.

   It is a critical to understand that the concept of reachability
   described above depends upon a knowledge or awareness of an address
   in the DNS.  Thus, in order to establish reachability to an end
   point, a host is dependent upon looking up an IP address in the DNS
   when a FQDN is used.  When DNS whitelisting is used, it is quite
   likely the case that an IPv6-enabled end user host could ping or
   connect to an example server host, even though the FQDN associated
   with that server host is restricted via a DNS whitelist.  Since most
   Internet applications and hosts such as web servers depend upon the
   DNS, and as end users connect to FQDNs such as www.example.com and do
   not remember or wish to type in an IP address, the notion of
   reachability described here should be understood to include knowledge
   how to associate a name with a network address.

7.3.  Operational Implications

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

7.3.1.  De-Whitelisting May Occur

   It is possible for a DNS recursive resolver added to a whitelist to
   then be removed from the whitelist, also known as de-whitelisting.
   Since de-whitelisting can occur, through a decision by the
   authoritative server operator, 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 7.3.6, 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.

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

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 large numbers of DNS whitelisting applications as
   part of their own IPv6 transition, 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 anticipation of interesting domains is
   likely infeasible, it is more likely that 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
   that they can ascertain to be engaging in DNS whitelisting.

   When 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 6 and may vary
   depending upon whether DNS whitelisting is universally deployed or is
   deployed on an ad hoc basis.

   These operators (of recursive resolvers) 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 large 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



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   represent for 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.

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 7.3.6.

   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.  Authoritative nameserver
   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.

7.3.5.  Implications of Operational Momentum

   It seems plausible that once DNS whitelisting is implemented it will
   be very difficult to deprecate such technical and operational
   practices.  This assumption is based in an understanding of human
   nature, not to mention physics.  For example, as Sir Issac Newton
   noted, "Every object in a state of uniform motion tends to remain in
   that state of motion unless an external force is applied to it" [Laws
   of Motion].  Thus, once DNS whitelisting is implemented it is quite
   likely that it would take considerable effort to deprecate the
   practice and remove it everywhere on the Internet - it will otherwise
   simply remain in place in perpetuity.  To better illustrate this
   point, one could consider one example (of many) that there are many
   email servers continuing to attempt to query or otherwise check anti-



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   spam DNS blocklists which have long ago ceased to exist.

7.3.6.  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
   the process of determining why a server is not reachable
   significantly more complex.

7.3.7.  Additional Implications If Deployed On An Ad Hoc Basis

   Additional implications, should this be deployed on an ad hoc basis,
   could include scalability problems relating to operational processes,
   monitoring, and ACL updates.  In particular, it seems likely that as
   the number of domains that are using DNS whitelisting increases, as
   well as the number of IPv6-capable networks requesting to be
   whitelisted, that there is an increased likelihood of configuration
   and other operational errors, especially with respect to the ACLs
   themselves.

   It is unclear when and if it would be appropriate to change from
   whitelisting to blacklisting, and whether or how this could feasibly
   be coordinated across the Internet, which may be proposed or
   implemented on an ad hoc basis when a majority of networks (or
   allocated IPv6 address blocks) have been whitelisted.  Finally, some
   parties implementing DNS whitelisting consider this to be a temporary
   measure.  As such, it is not clear how these parties will judge the
   network conditions to have changed sufficiently to justify disabling
   DNS whitelisting and/or what the process and timing will be in order
   to discontinue this practice.

   One further potential implication is that an end user with only an
   IPv4 address, using a DNS resolver which has not been whitelisted by
   any domains, would not be able to get any AAAA resource records.  In
   such a case, this could give that end user the incorrect impression
   that there is no IPv6-based content on the Internet since they are
   unable to discover any IPv6 addresses via the DNS.

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



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   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 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 major domains (meaning
   domains which are a major destination of Internet traffic)
   implementing DNS whitelisting, may be to encourage a return to more
   homogenous and/or controlled end user hosts.  This could have
   unintended side effects on and counter-productive implications for
   future innovation at the edges of the network.

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



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   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, a domain could withhold adding a network to their
   DNS whitelisting unless that network agreed to some sort of financial
   payment, legal agreement, agreement to sever a relationship with a
   competitor of the domain, etc.  In another example, a music-oriented
   domain may be engaged in some sort of dispute with an academic
   network concerning copyright infringement concerns within that
   network, and may choose to de-whitelist that network as a negotiating
   technique in some sort of commercial discussion.  In a final example,
   a major email domain may choose to de-whitelist a network due to that
   network sending some large volume of spam, which would have the
   effect of preventing other, end users on that network from using
   other, non-email-related applications within that domain.  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 4, 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



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   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 that are likely to be
   concerned over the negative implications of DNS whitelisting could
   logically be concerned of the negative effects that this practice
   could have on the adoption of IPv6 if it became widespread or was
   adopted by majors Internet domains or other major parties in the
   Internet ecosystem.

   At the same time, as noted in Section 3, some highly-trafficked
   domains may find the prospect of transitioning to IPv6 daunting
   without having some short-term ability to incrementally control the
   amount and source of IPv6 traffic to their domains.


8.  Solutions

   This section outlines several possible solutions when considering DNS
   whitelisting and associated IPv6-related issues.

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.

8.2.  Implement DNS Whitelisting On An Ad Hoc Basis

   If DNS whitelisting is to be adopted, 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.  Also in this scenario, ad hoc use by
   a particular domain may be a temporary measure that has been adopted
   to ease the transition of the domain to IPv6 over some short-term
   timeframe.

8.3.  Do Not Implement DNS Whitelisting

   As an alternative to adopting DNS whitelisting, the Internet
   community generally can 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.






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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.  Section 11 may also be
   relevant in this case.

   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.

   Despite any potential challenges, many in the Internet community are
   already working towards this goal and/or have expressed a general
   preference for this approach.

8.3.2.  Gain Experience Using IPv6 Transition Names

   Another alternative is for domains to gain experience using an FQDN
   which has become common for domains beginning the transition to IPv6;
   ipv6.example.com and www.ipv6.example.com.  This can be a way for a
   domain to gain IPv6 experience and increase IPv6 use on a relatively
   controlled basis, and to inform any plans for DNS whitelisting with
   experience.


9.  Is DNS Whitelisting a Recommended Practice?

   Opinions in the Internet community concerning whether or not DNS
   whitelisting is a recommended practice are understandably quite
   varied.  However, there is clear consensus that DNS whitelisting is
   at best a useful temporary measure which a domain may choose to
   pursue as they prepare for the transition to IPv6.  In particular,
   some major domains view DNS whitelisting as one of the few practical
   and low risk approaches enabling them to prepare for the transition
   to IPv6.  Thus, DNS whitelisting is not a recommended practice over
   the long-term.  In addition, DNS whitelisting should be avoided
   wherever possible in the short-term and its use is generally



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   discouraged.  Nevertheless, major domains may find DNS whitelisting a
   beneficial temporary tactic in their transition to IPv6.  Such
   temporary use during the transition to IPv6 is broadly accepted
   within the community, so long as it does not become a long-term
   practice.

   World IPv6 Day, sponsored by the Internet Society [World IPv6 Day],
   is scheduled to occur on June 8, 2011.  This will be an opportunity
   for domains to add AAAA resource records to the DNS without using DNS
   whitelisting.  As a result, this is likely an excellent opportunity
   for domains to evaluate the utility or necessity of DNS whitelisting,
   even in the short-term.  A major German news website, Heise Online,
   also ran a similar IPv6 experiment whereby they added AAAA resource
   records and observed and measured any errors [Heise Online
   Experiment], which is important reading for any domain contemplating
   either the use of DNS whitelisting or simply adding IPv6 addressing
   to their site.


10.  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
   resource 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
   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:

10.1.  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



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   which resolver server has sent a query, the DNSSEC chain of trust is
   not altered.  Even though the authoritative server will not always
   return a AAAA resource record when one exists, respective A resource
   records and AAAA resource records can and should both be signed.
   Therefore there are no DNSSEC implications per se.  However, any
   implementer of DNS whitelisting should be careful if they implement
   both DNSSEC signing of their domain and also DNS whitelisting of that
   same domain.  Specifically, those domains should ensure that resource
   records are being appropriately and reliably signed, which may
   present incremental operational and/or technical challenges.

   However, as noted in Section 3, end user networks may also choose to
   implement tools at their disposal in order to address IPv6-related
   impairments.  One of those possible tools could involve unspecified
   changes to the configuration of their recursive resolvers.  If it is
   a Security-Aware Resolver, modifying or suppressing AAAA resource
   records for a DNSSEC-signed domain will be problematic and could
   break the chain of trust established with DNSSEC.

10.2.  Authoritative DNS Response Consistency Considerations

   In addition to the considerations raised in Section 10.1, it is
   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.  While
   this may seem a somewhat obscure concern, domains nonetheless may
   wish to consider this when contemplating whether or not to pursue DNS
   whitelisting.


11.  Privacy Considerations

   As noted in Section 8.3.1, there may be methods to detect IPv6-
   related impairments for a particular end user.  For example, this may
   be possible when an end user visits the website of a particular
   domain.  In that example, there are likely no privacy considerations
   in communicating to that end user that the domain has detected a
   particular impairment.  However, if that domain decided to share
   information concerning that particular end user with their network
   operator or another party, then the visited domain may wish to in
   some manner advise the end user of this or otherwise seek their
   consent to such information sharing.  This may be achieved in a wide
   variety of ways, from presenting a message asking the user for
   consent (which will of course help them solve a technical problem of
   which they are likely unaware) to adding this to a domain's website



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   terms of use / service.  Such information sharing and communication
   of such sharing to end users may well vary by geographic area and/or
   legal jurisdiction.  Thus, a domain should consider any potential
   privacy issues these sorts of scenarios.


12.  IANA Considerations

   There are no IANA considerations in this document.


13.  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

   - Tom Klieber

   - Yiu Lee

   - Rich Woundy


14.  Acknowledgements

   The author and contributors also wish to acknowledge the assistance
   of the following individuals.  Some of these people provided helpful
   and important guidance in the development of this document and/or in
   the development of the concepts covered in this document.  Other
   people assisted by performing a detailed review of this document, and
   then providing feedback and constructive criticism for revisions to
   this document.  All of this was helpful and therefore the following
   individuals merit acknowledgement:

   - Bernard Aboba

   - Frank Bulk

   - Brian Carpenter

   - Karsten Fleischhauer

   - Wesley George



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   - Jerry Huang

   - Joel Jaeggli

   - Erik Kline

   - Suresh Krishnan

   - Victor Kuarsingh

   - Danny McPherson

   - Martin Millnert

   - Thomas Narten

   - Hannes Tschofenig

   - Tina Tsou


15.  References

15.1.  Normative References

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

   [RFC1918]  Rekhter, Y., Moskowitz, R., Karrenberg, D., Groot, G., and
              E. Lear, "Address Allocation for Private Internets",
              BCP 5, RFC 1918, February 1996.

   [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.




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   [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.

   [RFC4213]  Nordmark, E. and R. Gilligan, "Basic Transition Mechanisms
              for IPv6 Hosts and Routers", RFC 4213, October 2005.

15.2.  Informative References

   [Evaluating IPv6 Adoption]
              Colitti, L., Gunderson, S., Kline, E., and T. Refice,
              "Evaluating IPv6 adoption in the Internet", Passive and
              Active Management (PAM) Conference 2010, April 2010,
              <http://www.google.com/research/pubs/archive/36240.pdf>.

   [Heise Online Experiment]
              Heise.de, "World IPv6 Day - June 8, 2011", Heise.de
              Website http://www.h-online.com, January 2011, <http://
              www.h-online.com/features/
              The-big-IPv6-experiment-1165042.html>.

   [I-D.shirasaki-nat444]
              Yamagata, I., Shirasaki, Y., Nakagawa, A., Yamaguchi, J.,
              and H. Ashida, "NAT444", draft-shirasaki-nat444-03 (work
              in progress), January 2011.

   [IETF-77-DNSOP]
              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>.

   [IPv6 Brokenness]
              Anderson, T., "Measuring and Combating IPv6 Brokenness",
              Reseaux IP Europeens (RIPE) 61st Meeting, November 2011,
              <http://ripe61.ripe.net/presentations/162-ripe61.pdf>.

   [IPv6 Whitelist Operations]
              Kline, E., "IPv6 Whitelist Operations", Google Google IPv6
              Implementors Conference, June 2010, <http://



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              sites.google.com/site/ipv6implementors/2010/agenda/
              IPv6_Whitelist_Operations.pdf>.

   [Laws of Motion]
              Newton, I., "Mathematical Principles of Natural Philosophy
              (Philosophiae Naturalis Principia Mathematica)",
              Principia Mathematical Principles of Natural Philosophy
              (Philosophiae Naturalis Principia Mathematica), July 1687,
              <http://en.wikipedia.org/wiki/Newton's_laws_of_motion>.

   [NW-Article-DNS-WL]
              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>.

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

   [RFC1794]  Brisco, T., "DNS Support for Load Balancing", RFC 1794,
              April 1995.

   [RFC2782]  Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for
              specifying the location of services (DNS SRV)", RFC 2782,
              February 2000.

   [Resolvers in the Wild]
              Ager, B., Smaragdakis, G., Muhlbauer, W., and S. Uhlig,
              "Comparing DNS Resolvers in the Wild", ACM Sigcomm
              Internet Measurement Conference 2010, November 2010,
              <http://conferences.sigcomm.org/imc/2010/papers/p15.pdf>.

   [Rethinking 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>.



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   [Whitelisting Concerns]
              Brzozowski, J., Griffiths, C., Klieber, T., Lee, Y.,
              Livingood, J., and R. Woundy, "IPv6 DNS Whitelisting -
              Could It Hinder IPv6 Adoption?", ISOC Internet Society
              IPv6 Deployment Workshop, April 2010, <http://
              www.comcast6.net/
              IPv6_DNS_Whitelisting_Concerns_20100416.pdf>.

   [World IPv6 Day]
              The Internet Society, "World IPv6 Day - June 8, 2011",
              Internet Society Website http://www.isoc.org,
              January 2011, <http://isoc.org/wp/worldipv6day/>.


Appendix A.  Document Change Log

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

   -03: Several changes suggested by Joel Jaeggli at the end of WGLC.
   This involved swapping the order of Section 6.1 and 6.2, among other
   changes to make the document more readable, understandable, and
   tonally balanced.  As suggested by Karsten Fleischhauer, added a
   reference to RFC 4213 in Section 7.1, as well as other suggestions to
   that section.  As suggested by Tina Tsou, made some changes to the
   DNSSEC section regarding signing.  As suggested by Suresh Krishnan,
   made several changes to improve various sections of the document,
   such as adding an alternative concerning the use of ipv6.domain,
   improving the system logic section, and shortening the reference
   titles.  As suggested by Thomas Narten, added some text regarding the
   imperfection of making judgements as to end user host impairments
   based upon the recursive resolver's IP and/or network.  Finally, made
   sure that variations in the use of 'records' and 'resource records'
   was updated to 'resource records' for uniformity and to avoid
   confusion.

   -02: Called for and closed out feedback on dnsop and v6ops mailing
   lists.  Closed out open feedback items from IETF 79.  Cleared I-D
   nits issues, added a section on whether or not this is recommended,
   made language less company-specific based on feedback from Martin
   Millnert, Wes George, and Victor Kuarsingh.  Also mentioned World
   IPv6 Day per Wes George's suggestion.  Added references to the ISOC
   World IPv6 Day and the Heise.de test at the suggestion of Jerry
   Huang, as well as an additional implication in 7.3.7.  Made any
   speculation on IPv4 impairment noted explicitly as such, per feedback
   from Martin Millnert.  Added a reference to DNS SRV in the load
   balancing section.  Added various other references.  Numerous changes
   suggested by John Brzozowski in several sections, to clean up the
   document.  Moved up the section on why whitelisting is performed to



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   make the document flow more logically.  Added a note in the ad hoc
   deployment scenario explaining that a deployment may be temporary,
   and including more of the perceived benefits of this tactic.  Added a
   Privacy Considerations section to address end-user detection and
   communication.

   -01: Incorporated feedback received from Brian Carpenter (from 10/19/
   2010), Frank Bulk (from 11/8/2010), and Erik Kline (from 10/1/2010).
   Also added an informative reference at the suggestion of Wes George
   (from from 10/22/2010).  Closed out numerous editorial notes, and
   made a variety of other changes.

   -00: First version published as a v6ops WG draft.  The preceding
   individual draft was
   draft-livingood-dns-whitelisting-implications-01.  IMPORTANT TO NOTE
   that no changes have been made yet based on WG and list feedback.
   These are in queue for a -01 update.


Appendix B.  Open Issues

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

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


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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