IPv6 Operations J. Livingood
Internet-Draft Comcast
Intended status: Informational January 25, 2011
Expires: July 29, 2011
IPv6 AAAA DNS Whitelisting Implications
draft-ietf-v6ops-v6-aaaa-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
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This Internet-Draft will expire on July 29, 2011.
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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 Other DNS Operations . . . . . . . . . . . . . 9
4.1. Similarities to Split DNS . . . . . . . . . . . . . . . . 9
4.2. Similarities to DNS Load Balancing . . . . . . . . . . . . 10
5. Likely Deployment Scenarios . . . . . . . . . . . . . . . . . 11
5.1. Deploying DNS Whitelisting Universally . . . . . . . . . . 11
5.2. Deploying DNS Whitelisting On An Ad Hoc Basis . . . . . . 12
6. What Problems Are DNS Whitelisting Implementers Trying To
Solve? . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
7. Implications of DNS Whitelisting . . . . . . . . . . . . . . . 13
7.1. Architectural Implications . . . . . . . . . . . . . . . . 13
7.2. Public IPv6 Address Reachability Implications . . . . . . 14
7.3. Operational Implications . . . . . . . . . . . . . . . . . 15
7.3.1. De-Whitelisting May Occur . . . . . . . . . . . . . . 15
7.3.2. Authoritative DNS Server Operational Implications . . 16
7.3.3. DNS Recursive Resolver Server Operational
Implications . . . . . . . . . . . . . . . . . . . . . 16
7.3.4. Monitoring Implications . . . . . . . . . . . . . . . 17
7.3.5. Implications of Operational Momentum . . . . . . . . . 17
7.3.6. Troubleshooting Implications . . . . . . . . . . . . . 18
7.3.7. Additional Implications If Deployed On An Ad Hoc
Basis . . . . . . . . . . . . . . . . . . . . . . . . 18
7.4. Homogeneity May Be Encouraged . . . . . . . . . . . . . . 18
7.5. Technology Policy Implications . . . . . . . . . . . . . . 19
7.6. IPv6 Adoption Implications . . . . . . . . . . . . . . . . 20
8. Solutions . . . . . . . . . . . . . . . . . . . . . . . . . . 21
8.1. Implement DNS Whitelisting Universally . . . . . . . . . . 21
8.2. Implement DNS Whitelisting On An Ad Hoc Basis . . . . . . 21
8.3. Do Not Implement DNS Whitelisting . . . . . . . . . . . . 21
8.3.1. Solving Current End User IPv6 Impairments . . . . . . 21
9. Security Considerations . . . . . . . . . . . . . . . . . . . 22
9.1. DNSSEC Considerations . . . . . . . . . . . . . . . . . . 22
9.2. Authoritative DNS Response Consistency Considerations . . 23
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 23
11. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 23
12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 23
13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 24
13.1. Normative References . . . . . . . . . . . . . . . . . . . 24
13.2. Informative References . . . . . . . . . . . . . . . . . . 25
Appendix A. Document Change Log . . . . . . . . . . . . . . . . . 26
Appendix B. Open Issues . . . . . . . . . . . . . . . . . . . . . 26
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 27
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1. Introduction
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, such as Google's various websites. These
web site operators, or domain 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 domains have begun to either implement DNS whitelisting
or strongly consider the implementation of DNS whitelisting [Network
World Article on DNS Whitelisting] [IPv6 Whitelist Operations]. 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.
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.
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.
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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. While these are not network-layer access
controls, they are nonetheless access controls that are a factor for
both end users and are directly related to the transition of one
network address family to another (IPv4 to IPv6).
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
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 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, including ISPs like Comcast,
are concerned that this emerging practice of DNS whitelisting for
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IPv6 address records could represent a departure from the generally
accepted practices regarding IPv4 address records in the DNS on the
Internet [IPv6 DNS Whitelisting - Could It Hinder IPv6 Adoption?].
These parties 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
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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
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.
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.
4. Similarities to Other DNS Operations
Some aspects of DNS whitelisting may be considered similar in some
ways to other common DNS operational techniques, which is explored
briefly below.
4.1. Similarities to Split DNS
DNS whitelisting has some similarities 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
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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."
4.2. Similarities to DNS Load Balancing
DNS whitelisting also has some similarities to DNS load balancing.
There are many ways that DNS load balancing can be performed, and of
course this can mean many things to different people. In one
example, multiple IP address resource records (A or AAAA) can be
added to the DNS to resolve a given FQDN, which is referred to as DNS
round robin [REFERENCE AVAILABLE?]. In another example, one or more
of the IP address resource records in the DNS will direct traffic to
a load balancer [REFERENCE AVAILABLE?]. 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
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. In
addition, a geographically-aware authoritative DNS server may be
used, as is common with Content Delivery Networks (CDNs), 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 [REFERENCE AVAILABLE?]. 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 returned to
resolvers based on the IP address of each resolver (or other imputed
factors related to that IP address). However, what is different of
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course, if that in this case the resolvers are not necessarily
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.
5. 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 likely deployment scenarios below, it is possible
that reputable third parties could create and maintain these DNS
whitelists, in much the same way that blacklists are used for
reducing email spam. In this email example, 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. Thus, a similar model could emerge for DNS
whitelisting, whether deployment occurs universally or on an ad hoc
basis.
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
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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.
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.
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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.
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.
In addition, Google has noted that they have received requests to not
send DNS responses with AAAA resource records to particular
resolvers. In these cases, the operators of those recursive
resolvers have expressed a concern that their IPv6 network
infrastructure is not yet ready to handle the traffic volume which
may be associated with the hosts in their network connecting to
Google websites, such as YouTube. In this case, this is clearly a
temporary concern relating to the deployment of IP 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, 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).
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 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
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the DNS resolution path 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. In this case, the middle network should be understood
to mean anything other than the end hosts involved in communicating
with one another. Obviously 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.
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
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. Of course, this is a
generalization and in Section 4 there are examples of common cases
where this may not necessarily be the case. In any case, for the
purposes of this document, 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
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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.
In addition, establishing DNS whitelisting as an accepted practice in
the early phases of mass IPv6 deployment could well establish DNS
whitelisting as an integral part of how IPv6 is 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 the
Internet of the future that we will all live with for a long time.
However, 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. Thus, when DNS whitelisting is used, it
is quite likely the case that a end user host could ping a example
server host, even though the FQDN associated with that server host is
restricted via a DNS whitelist. But 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 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 7.3.6, and Section 7.5.
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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,
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.
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
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of new domains, readers should not underestimate the potential
significance in personnel and expense that this could 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. 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.
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"
[Newton's Laws of Motion]. Thus, once DNS whitelisting is
implemented it is quite likely that it would take considerable effort
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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 in one example (of many)
that here are likely many email servers continuing to attempt to
query or otherwise check anti-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 quite likely
that as the number of domains that are whitelisted 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 also unclear when and if it would be appropriate to change from
whitelisting to blacklisting, and whether/how this could feasibly be
coordinated across the Internet, which may be proposed 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 turn off and stop this
practice.
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
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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 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. Unfortunately, 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
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.
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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 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 that are likely to be
concerned over the negative implications of DNS whitelisting could
logically be concerned of the negative effects that this practice
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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.
8. Solutions
This section outline 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 was 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 also 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 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
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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.
Despite any potential challenges, many in the Internet community are
already working towards this goal and/or have expressed a preference
for this approach.
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
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.
However, any implementer of DNS whitelisting should be quite careful
if they implement both DNSSEC signing of their domain and also DNS
whitelisting of that same domain. Specifically, those domains should
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ensure that records are being appropriately and reliably signed,
which may well prove operationally and/or technically challenging.
9.2. Authoritative DNS Response Consistency Considerations
In addition to the considerations raised in Section 9.1, 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.
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
- Tom Klieber
- Yiu Lee
- Rich Woundy
12. 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
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individuals merit acknowledgement:
- Bernard Aboba
- Frank Bulk
- Brian Carpenter
- Wesley George
- Erik Kline
- Danny McPherson
- Hannes Tschofenig
13. References
13.1. 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.
[RFC4033] Arends, R., Austein, R., Larson, M., Massey, D., and S.
Rose, "DNS Security Introduction and Requirements",
RFC 4033, March 2005.
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[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.
13.2. Informative References
[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 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>.
[IPv6 DNS Whitelisting - Could It Hinder IPv6 Adoption?]
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>.
[IPv6 Whitelist Operations]
Kline, E., "IPv6 Whitelist Operations", Google Google IPv6
Implementors Conference, June 2010, <http://
sites.google.com/site/ipv6implementors/2010/agenda/
IPv6_Whitelist_Operations.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>.
[Newton's Laws of Motion]
Newton, I., "Mathematical Principles of Natural Philosophy
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(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>.
[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]
-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. Close the issues below and any feedback from the v6ops and dnsop
mailing lists in a -02 update, then request WGLC
2. Perform an second review of notes from IETF 79 to ensure that all
feedback received then has been fully taken into account!
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3. Add any good references throughout the document - posed in
question to v6ops
4. Ensure references are in the proper section (normative/
informative)
5. Include a number of references from RFC3724?
6. Add brokenness reference to
http://ripe61.ripe.net/presentations/162-ripe61.pdf
7. Should I include a full list or other details of the root causes
of IPv6 brokenness? - posed in question to v6ops
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
Livingood Expires July 29, 2011 [Page 27]
