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IETF RFC 7535
Last modified on Wednesday, May 13th, 2015
 Permanent link to RFC 7535
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Internet Engineering Task Force (IETF) J. Abley
Request for Comments: 7535 Dyn, Inc.
Category: Informational B. Dickson
ISSN: 2070-1721 Twitter, Inc.
W. Kumari
Google
G. Michaelson
APNIC
May 2015
AS112 Redirection Using DNAME
 Abstract
AS112 provides a mechanism for handling reverse lookups on IP
addresses that are not unique (e.g., RFC 1918 addresses). This
document describes modifications to the deployment and use of AS112
infrastructure that will allow zones to be added and dropped much
more easily, using DNAME resource records.
This approach makes it possible for any DNS zone administrator to
sink traffic relating to parts of the global DNS namespace under
their control to the AS112 infrastructure without coordination with
the operators of AS112 infrastructure.
Status of This Memo
This document is not an Internet Standards Track specification; it is
published for informational purposes.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Not all documents
approved by the IESG are a candidate for any level of Internet
Standard; see Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/RFC 7535.
Abley, et al. Informational PAGE 1 
RFC 7535 AS112 Redirection Using DNAME May 2015
Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction ....................................................3
2. Design Overview .................................................4
3. AS112 Operations ................................................5
3.1. Extensions to Support DNAME Redirection ....................5
3.2. Redirection of Query Traffic to AS112 Servers ..............5
4. Continuity of AS112 Operations ..................................6
5. Candidate Zones for AS112 Redirection ...........................6
6. DNAME Deployment Considerations .................................7
7. IAB Statement Regarding This .ARPA Request ......................8
8. IANA Considerations .............................................8
8.1. Address Assignment .........................................8
8.2. Hosting of AS112.ARPA .....................................10
8.3. Delegation of AS112.ARPA ..................................10
9. Security Considerations ........................................10
10. References ....................................................11
10.1. Normative References .....................................11
10.2. Informative References ...................................11
Appendix A. Assessing Support for DNAME in the Real World .........13
A.1. Methodology ................................................13
A.2. Results ....................................................15
Acknowledgements ..................................................16
Authors' Addresses ................................................16
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RFC 7535 AS112 Redirection Using DNAME May 2015
1. Introduction
Many sites connected to the Internet make use of IPv4 addresses that
are not globally unique. Examples are the addresses designated in
[RFC 1918] for private use within individual sites.
Devices in such environments may occasionally originate Domain Name
System (DNS) queries (so-called "reverse lookups") corresponding to
those private-use addresses. Since the addresses concerned have only
local significance, it is good practice for site administrators to
ensure that such queries are answered locally. However, it is not
uncommon for such queries to follow the normal delegation path in the
public DNS instead of being answered within the site.
It is not possible for public DNS servers to give useful answers to
such queries. In addition, due to the wide deployment of private-use
addresses and the continuing growth of the Internet, the volume of
such queries is large and growing. The AS112 project aims to provide
a distributed sink for such queries in order to reduce the load on
the IN-ADDR.ARPA authoritative servers. The AS112 project is named
after the Autonomous System Number (ASN) that was assigned to it.
Prior to implementation of this technique, the AS112 project did not
accommodate the addition and removal of DNS zones elegantly. Since
additional zones of definitively local significance are known to
exist, this presents a problem. This document describes
modifications to the deployment and use of AS112 infrastructure that
will allow zones to be added and dropped much more easily.
The AS112 project is described in detail in [RFC 7534].
The AS112 nameservers (PRISONER.IANA.ORG, BLACKHOLE-1.IANA.ORG, and
BLACKHOLE-2.IANA.ORG) are required to answer authoritatively for each
and every zone that is delegated to them. If a zone is delegated to
AS112 nameservers without those nameservers being configured ahead of
time to answer authoritatively for that zone, there is a detrimental
impact on clients following referrals for queries within that zone.
This misconfiguration is colloquially known as a "lame delegation".
AS112 nameserver operators are only loosely coordinated, and hence
adding support for a new zone (or, correspondingly, removing support
for a zone that is no longer delegated to the AS112 nameservers) is
difficult to accomplish with accuracy. Testing AS112 nameservers
remotely to see whether they are configured to answer authoritatively
for a particular zone is similarly challenging, since AS112 nodes are
distributed using anycast [RFC 4786].
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RFC 7535 AS112 Redirection Using DNAME May 2015
This document defines a more flexible approach for sinking queries on
AS112 infrastructure that can be deployed alongside unmodified,
existing AS112 nodes. Instead of delegating additional zones
directly to AS112 nameservers, DNAME [RFC 6672] redirection is used.
This approach has the advantage that query traffic for arbitrary
parts of the namespace can be directed to AS112 servers without those
servers having to be reconfigured every time a zone is added or
removed.
This approach makes it possible for any DNS zone administrator to
sink traffic relating to parts of the global DNS namespace under
their control to the AS112 infrastructure without coordination with
the operators of AS112 infrastructure.
2. Design Overview
A new zone, EMPTY.AS112.ARPA, is delegated to a single nameserver
BLACKHOLE.AS112.ARPA (IPv4 address 192.31.196.1, IPv6 address
2001:4:112::1).
The IPv4 address 192.31.196.1 has been selected from the prefix
assigned by the IANA such that the address is coverable by a single
IPv4 /24 prefix, and that no other address covered by that prefix is
in use. The IPv6 address 2001:4:112::1 has been similarly assigned
such that no other address within a covering /48 is in use. This
addressing plan accommodates the anycast distribution of the
BLACKHOLE.AS112.ARPA service using a single IPv4 service prefix and a
single IPv6 service prefix. See [RFC 4786] for more discussion of
anycast service distribution; see Section 8 for the specific actions
completed by IANA per this document.
Some or all of the existing AS112 nodes should be extended to support
these new nameserver addresses and to host the EMPTY.AS112.ARPA zone.
See [RFC 7534] for revised guidance to AS112 server operators.
Each part of the DNS namespace for which it is desirable to sink
queries at AS112 nameservers should be redirected to the
EMPTY.AS112.ARPA zone using DNAME [RFC 6672]. See Section 3.2 for
guidance to zone administrators.
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RFC 7535 AS112 Redirection Using DNAME May 2015
3. AS112 Operations
3.1. Extensions to Support DNAME Redirection
Guidance to operators of AS112 nodes is extended to include
configuration of the 192.31.196.1 and 2001:4:112::1 addresses, and
the corresponding announcement of covering routes for those
addresses, and to host the EMPTY.AS112.ARPA zone.
IPv4-only AS112 nodes should only configure the 192.31.196.1
nameserver address; IPv6-only AS112 nodes should only configure the
2001:4:112::1 nameserver address.
It is only necessary for a single AS112 server operator to implement
these extensions for this mechanism to function as intended. It is
beneficial if many more than one AS112 server operator makes these
changes, however, since that provides for greater distribution and
capacity for the nameservers serving the EMPTY.AS112.ARPA zone. It
is not necessary for all AS112 server operators to make these changes
for the mechanism to be viable.
Detailed instructions for the implementation of these extensions are
included in [RFC 7534].
3.2. Redirection of Query Traffic to AS112 Servers
Once the EMPTY.AS112.ARPA zone has been deployed using the
nameservers described in Section 3.1, redirections may be installed
in the DNS namespace for queries that are intended to be answered by
the AS112 infrastructure.
For example, reverse queries corresponding to TEST-NET-1
(192.0.2.0/24) [RFC 5737] could be redirected to AS112 nameservers by
installing a DNAME resource record in the 192.IN-ADDR.ARPA zone, as
illustrated in Figure 1.
$ORIGIN 192.IN-ADDR.ARPA.
...
2.0 IN DNAME EMPTY.AS112.ARPA.
...
Figure 1
There is no practical limit to the number of redirections that can be
configured in this fashion. Redirection of a particular part of the
namespace to EMPTY.AS112.ARPA can be removed at any time, under the
control of the administrators of the corresponding part of the DNS
namespace. No changes to deployed AS112 nodes incorporating the
Abley, et al. Informational PAGE 5
RFC 7535 AS112 Redirection Using DNAME May 2015
extensions described in this document are required to support
additional redirections. A list of possible candidates for AS112
redirection can be found in Section 5.
DNAME resource records deployed for this purpose can be signed with
DNSSEC [RFC 4033], providing a secure means of authenticating the
legitimacy of each redirection.
4. Continuity of AS112 Operations
Existing guidance to AS112 server operators to accept and respond to
queries directed at the PRISONER.IANA.ORG, BLACKHOLE-1.IANA.ORG, and
BLACKHOLE-2.IANA.ORG nameservers should continue to be followed, and
no changes to the delegation of existing zones hosted on AS112
servers should occur. These measures are intended to provide
continuity of operations for zones currently delegated to AS112
servers and avoid any accidental client impact due to the changes
proposed in this document.
Once it has become empirically and quantitatively clear that the
EMPTY.AS112.ARPA zone is well hosted to the extent that it is thought
that the existing, unmodified AS112 servers host 10.IN-ADDR.ARPA, the
decision might be made to replace the delegation of those [RFC 1918]
zones with DNAME redirection. Once implemented, the
PRISONER.IANA.ORG, BLACKHOLE-1.IANA.ORG, and BLACKHOLE-2.IANA.ORG
nameservers could be retired. This document gives no such direction
to the IANA, however.
5. Candidate Zones for AS112 Redirection
All zones listed in [RFC 6303] are candidates for AS112 redirection.
Since no pre-provisioning is required on the part of AS112 operators
to facilitate sinking of any name in the DNS namespace by AS112
infrastructure, this mechanism supports AS112 redirection by any zone
owner in the DNS.
This document is simply concerned with provision of the AS112
redirection service and does not specify that any particular AS112
redirection be put in place.
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RFC 7535 AS112 Redirection Using DNAME May 2015
6. DNAME Deployment Considerations
DNAME was specified years after the original implementations of
[RFC 1035], and hence universal deployment cannot be expected.
[RFC 6672] specifies a fallback mechanism that makes use of
synthesised CNAME RRSets for this reason. The expectation that
design choices in the DNAME specification ought to mitigate any lack
of deployment is reviewed below. Experimental validation of those
expectations is included in Appendix A.
It is a fundamental design requirement of AS112 service that
responses be cached. We can safely declare DNAME support on the
authoritative server to be a prerequisite for DNAME redirection, but
the cases where individual elements in resolver chains do not support
DNAME processing deserve closer examination.
The expected behaviour when a DNAME response is supplied to a
resolver that does not support DNAME is that the accompanying,
synthesised CNAME will be accepted and cached. Re-query frequency
will be determined by the TTLs (Time to Live) returned by the
DNAME-responding authoritative servers.
Resolution of the CNAME target is straightforward and functions
exactly as the AS112 project has operated since it was deployed. The
negative caching [RFC 2308] of the CNAME target follows the parameters
defined in the target zone, EMPTY.AS112.ARPA. This has the side
effects that all redirected names ultimately landing on an AS112 node
will be negatively cached with the same parameters, but this lack of
flexibility seems non-controversial; the effect of reducing the
negative cache TTL would be increased query volume on the AS112 node
operator concerned, and hence controls seem well aligned with
operation.
Validating resolvers (i.e., those requesting and processing DNSSEC
[RFC 4033] metadata) are required to implement DNAME and hence should
not make use of synthesised CNAME RRs. The lack of signature over a
received CNAME RR should hence not limit the ability to sign the
(DNAME) redirection point, and for those (DNAME) signatures to be
validated.
In the case where a recursive server implements DNAME but DNAME is
not implemented in a stub resolver, CNAME synthesis will again
provide a viable path.
DNAME support on AS112 nodes themselves is never required under this
proposal.
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RFC 7535 AS112 Redirection Using DNAME May 2015
7. IAB Statement Regarding This .ARPA Request
With the publication of this document, the IAB approves of the
delegation of 'AS112' in the ARPA domain. Under [RFC 3172], the IAB
has requested that IANA delegate and provision "AS112.ARPA" as
specified in this specification. However, the IAB does not take any
architectural or technical position about this specification.
8. IANA Considerations
8.1. Address Assignment
Per this document, IANA has assigned IPv4 and IPv6 number resources
in conformance with Section 4 of [RFC 2860].
The IANA has assigned one IPv4 /24 netblock and registered its use in
the "IANA IPv4 Special-Purpose Address Registry" [RFC 6890] as
follows:
+----------------------+-----------------+
| Name | Value |
+----------------------+-----------------+
| Address Block | 192.31.196.0/24 |
| | |
| Name | AS112-v4 |
| | |
| RFC | RFC 7535 |
| | |
| Allocation Date | 2014-12 |
| | |
| Termination Date | N/A |
| | |
| Source | True |
| | |
| Destination | True |
| | |
| Forwardable | True |
| | |
| Global | True |
| | |
| Reserved-by-Protocol | False |
+----------------------+-----------------+
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RFC 7535 AS112 Redirection Using DNAME May 2015
IANA has assigned one IPv6 /48 netblock and registered its use in the
"IANA IPv6 Special-Purpose Address Registry" [RFC 6890] as follows:
+----------------------+-----------------+
| Name | Value |
+----------------------+-----------------+
| Address Block | 2001:4:112::/48 |
| | |
| Name | AS112-v6 |
| | |
| RFC | RFC 7535 |
| | |
| Allocation Date | 2014-12 |
| | |
| Termination Date | N/A |
| | |
| Source | True |
| | |
| Destination | True |
| | |
| Forwardable | True |
| | |
| Global | True |
| | |
| Reserved-by-Protocol | False |
+----------------------+-----------------+
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RFC 7535 AS112 Redirection Using DNAME May 2015
8.2. Hosting of AS112.ARPA
The IANA hosts and signs the zone AS112.ARPA using nameservers and
DNSSEC signing infrastructure of their choosing, as shown in
Figure 2. SOA RDATA may be adjusted by the IANA to suit their
operational requirements.
$ORIGIN AS112.ARPA.
$TTL 3600
@ IN SOA BLACKHOLE.AS112.ARPA. NOC.DNS.ICANN.ORG. (
1 ; serial
10800 ; refresh
3600 ; retry
1209600 ; expire
3600 ) ; negative cache TTL
NS A.IANA-SERVERS.NET.
NS B.IANA-SERVERS.NET.
NS C.IANA-SERVERS.NET.
BLACKHOLE A 192.31.196.1
AAAA 2001:4:112::1
HOSTNAME NS BLACKHOLE
EMPTY NS BLACKHOLE
Figure 2
8.3. Delegation of AS112.ARPA
The IANA has arranged delegation from the ARPA zone according to
normal IANA procedure for ARPA zone management, to the nameservers
used in carrying out the direction in Section 8.2. The whois contact
information for the new record is specified by the IAB under
[RFC 3172].
9. Security Considerations
This document presents no known additional security concerns to the
Internet.
For security considerations relating to AS112 service in general, see
[RFC 7534].
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RFC 7535 AS112 Redirection Using DNAME May 2015
10. References
10.1. Normative References
[RFC 1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, DOI 10.17487/RFC 1035,
November 1987, <http://www.rfc-editor.org/info/RFC 1035>.
[RFC 2308] Andrews, M., "Negative Caching of DNS Queries (DNS
NCACHE)", RFC 2308, DOI 10.17487/RFC 2308, March 1998,
<http://www.rfc-editor.org/info/RFC 2308>.
[RFC 6672] Rose, S. and W. Wijngaards, "DNAME Redirection in the
DNS", RFC 6672, DOI 10.17487/RFC 6672, June 2012,
<http://www.rfc-editor.org/info/RFC 6672>.
[RFC 7534] Abley, J. and W. Sotomayor, "AS112 Nameserver Operations",
RFC 7534, DOI 10.17487/RFC 7534, May 2015,
<http://www.rfc-editor.org/info/RFC 7534>.
10.2. Informative References
[RFC 1918] Rekhter, Y., Moskowitz, B., Karrenberg, D., de Groot, G.,
and E. Lear, "Address Allocation for Private Internets",
BCP 5, RFC 1918, DOI 10.17487/RFC 1918, February 1996,
<http://www.rfc-editor.org/info/RFC 1918>.
[RFC 2860] Carpenter, B., Baker, F., and M. Roberts, "Memorandum of
Understanding Concerning the Technical Work of the
Internet Assigned Numbers Authority", RFC 2860,
DOI 10.17487/RFC 2860, June 2000,
<http://www.rfc-editor.org/info/RFC 2860>.
[RFC 3172] Huston, G., Ed., "Management Guidelines & Operational
Requirements for the Address and Routing Parameter Area
Domain ("arpa")", BCP 52, RFC 3172, DOI 10.17487/RFC 3172,
September 2001, <http://www.rfc-editor.org/info/RFC 3172>.
[RFC 4033] Arends, R., Austein, R., Larson, M., Massey, D., and S.
Rose, "DNS Security Introduction and Requirements",
RFC 4033, DOI 10.17487/RFC 4033, March 2005,
<http://www.rfc-editor.org/info/RFC 4033>.
[RFC 4786] Abley, J. and K. Lindqvist, "Operation of Anycast
Services", BCP 126, RFC 4786, DOI 10.17487/RFC 4786,
December 2006, <http://www.rfc-editor.org/info/RFC 4786>.
Abley, et al. Informational PAGE 11
RFC 7535 AS112 Redirection Using DNAME May 2015
[RFC 5737] Arkko, J., Cotton, M., and L. Vegoda, "IPv4 Address Blocks
Reserved for Documentation", RFC 5737,
DOI 10.17487/RFC 5737, January 2010,
<http://www.rfc-editor.org/info/RFC 5737>.
[RFC 6303] Andrews, M., "Locally Served DNS Zones", BCP 163,
RFC 6303, DOI 10.17487/RFC 6303, July 2011,
<http://www.rfc-editor.org/info/RFC 6303>.
[RFC 6890] Cotton, M., Vegoda, L., Bonica, R., Ed., and B. Haberman,
"Special-Purpose IP Address Registries", BCP 153,
RFC 6890, DOI 10.17487/RFC 6890, April 2013,
<http://www.rfc-editor.org/info/RFC 6890>.
Abley, et al. Informational PAGE 12
RFC 7535 AS112 Redirection Using DNAME May 2015
Appendix A. Assessing Support for DNAME in the Real World
To measure the extent to which the DNAME construct is supported in
the Internet, we have used an experimental technique to test the DNS
resolvers used by end hosts and derive from the test a measurement of
DNAME support within the Internet.
A.1. Methodology
The test was conducted by loading a user's browser with four URLs
to retrieve. The first three comprise the test setup, while the
final URL communicates the result to the experiment controller.
The URLs are:
A http://a.<unique_string>.dname.example.com/1x1.png?
a.<unique_string>.dname
B http://b.dname.example.com/1x1.png?
b.<unique_string>.dname
C http://c.<unique_string>.target.example.net/1x1.png?
c.<unique_string>.target
D http://results.recorder.example.net/1x1.png?
results.<unique_string>?za=<a_result>&zb=<b_result>&zc=<c_result>
The A URL is designed to test the end user's capability to resolve a
name that has never been seen before, so that the resolution of this
domain name will reliably result in a query at the authoritative
nameserver. This is intended to test the use of domain names where
there is a dynamic component that also uses the DNAME construct.
The B URL is deliberately designed to be cached by caching resolvers
that are used in the process of resolving the domain name.
The C URL is a control URL. This is a unique URL, similar to A, but
does not refer to a DNAME structure.
The D URL uses a static cacheable domain name.
The <unique_string> value is common to the four URLs used in each
individual instance of this test but varies from test to test. The
result is that each end user is presented with a unique string.
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RFC 7535 AS112 Redirection Using DNAME May 2015
The contents of the EXAMPLE.COM, TARGET.EXAMPLE.NET, and
RECORDER.EXAMPLE.NET zones are shown in Figure 3.
$ORIGIN EXAMPLE.COM.
...
DNAME. IN DNAME TARGET.EXAMPLE.NET.
...
$ORIGIN TARGET.EXAMPLE.NET.
...
B IN A 192.0.2.0
* IN A 192.0.2.0
...
$ORIGIN RECORDER.EXAMPLE.NET.
...
RESULTS IN A 192.0.2.0
...
Figure 3
The first three URLs (A, B, and C) are loaded as tasks into the
user's browser upon execution of the test's script. The script
starts a timer with each of these URLs to measure the elapsed time to
fetch the URL. The script then waits for the three fetches to
complete, or 10 seconds, whichever occurs first. The script then
loads the results of the three timers into the GET arguments of the
D URL and performs a fetch to pass these results back to the
experiment's server.
Logs on the web server reached at RESULTS.RECORDER.EXAMPLE.NET will
include entries of the form shown in Figure 4. If any of the URLs
fail to load within 10 seconds, the D URL will report the failure as
a "null" timer value.
GET /1x1.png?results.<unique_string>?za=1822&zb=1674&zc=1582
GET /1x1.png?results.<unique_string>?za=null&zb=null&zc=161
Figure 4
The script has been encoded in Adobe Flash with a simple image in the
form of an online advertisement. An online advertisement network has
been used to distribute the script. The script is invoked when the
advertisement is presented in the end user's browser or application
and does not require the user to click on the supplied image in any
way. The advertisement placement parameters were set to the broadest
possible scope to sample users from across the entire Internet.
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RFC 7535 AS112 Redirection Using DNAME May 2015
A.2. Results
The test was loaded into an advertisement distributed on 2013-10-10
and 2013-10-11.
+--------------------+---------+------------+
| | Count | Percentage |
+--------------------+---------+------------+
| Recorded Results: | 338,478 | |
| | | |
| A or B Loaded: | 331,896 | 98.1% |
| | | |
| A Fail and B Fail: | 6,492 | 1.9% |
| | | |
| A Fail and B Load: | 4,249 | 1.3% |
| | | |
| A Load and B Fail: | 1,624 | 0.5% |
| | | |
| C Fail: | 9,355 | 2.8% |
+--------------------+---------+------------+
Table 1
These results indicate that at most 1.9% of tested clients use DNS
resolvers that fail to resolve a domain name that contains a DNAME
redirection. However, the failure rate of slightly lower than 3% for
the control URL indicates that the failure rate for the DNAME
construct lies within the bounds of error within the experimental
framework. We conclude that there is no evidence of a consistent
failure on the part of deployed DNS resolvers to correctly resolve a
DNAME construct.
This experiment was conducted by Geoff Huston and George Michaelson.
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RFC 7535 AS112 Redirection Using DNAME May 2015
Acknowledgements
The authors acknowledge the valuable contributions of Bob Harold and
other participants in the DNSOP working group in the preparation of
this document.
Authors' Addresses
Joe Abley
Dyn, Inc.
103-186 Albert Street
London, ON N6A 1M1
Canada
Phone: +1 519 670 9327
EMail: jabley@dyn.com
Brian Dickson
Twitter, Inc.
EMail: bdickson@twitter.com
Warren Kumari
Google
1600 Amphitheatre Parkway
Mountain View, CA 94043
United States
EMail: warren@kumari.net
George Michaelson
APNIC
EMail: ggm@apnic.net
Abley, et al. Informational PAGE 16
RFC TOTAL SIZE: 31730 bytes
PUBLICATION DATE: Wednesday, May 13th, 2015
LEGAL RIGHTS: The IETF Trust (see BCP 78)
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