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Yeti DNS Testbed

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Document Type
This is an older version of an Internet-Draft that was ultimately published as RFC 8483.
Authors Linjian Song , Dong Liu , Paul A. Vixie , Akira Kato , Shane Kerr
Last updated 2018-06-19 (Latest revision 2018-05-22)
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Internet Engineering Task Force (IETF)                      L. Song, Ed.
Internet-Draft                                                    D. Liu
Intended status: Experimental                 Beijing Internet Institute
Expires: November 22, 2018                                      P. Vixie
                                            Keio University/WIDE Project
                                                                 S. Kerr
                                                            May 21, 2018

                            Yeti DNS Testbed


   The Internet's Domain Name System is designed and built on a single
   root, known as the Root Server System.

   Yeti DNS is an experimental, non-production root server testbed that
   provides an environment where technical and operational experiments
   can safely be performed without risk to production root server
   infrastructure.  Yeti DNS is an independently-coordinated project and
   is not affiliated with ICANN, IANA or any Root Server Operator.

   The Yeti DNS testbed implementation includes various novel and
   experimental components.  These differences from the Root Server
   System have operational consequences; by deploying such a system
   globally but outside the production DNS system, the Yeti DNS project
   provides an opportunity to gain insight into those consequences
   without threatening the stability of the DNS.

   This document neither addresses the relevant policies under which the
   Root Server System is operated nor makes any proposal for changing
   any aspect of its implementation or operation.  This document aims
   solely to document the technical and operational experience of
   deploying a system which is similar to but different from the Root
   Server System.

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

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   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 November 22, 2018.

Copyright Notice

   Copyright (c) 2018 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
   ( 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.  Requirements Notation and Conventions . . . . . . . . . . . .   5
   3.  Areas of Study  . . . . . . . . . . . . . . . . . . . . . . .   5
     3.1.  Implementation of a Root Server System-like Testbed . . .   5
     3.2.  Yeti-Root Zone Distribution . . . . . . . . . . . . . . .   5
     3.3.  Yeti-Root Server Names and Addressing . . . . . . . . . .   5
     3.4.  IPv6-Only Yeti-Root Servers . . . . . . . . . . . . . . .   5
     3.5.  DNSSEC in the Yeti-Root Zone  . . . . . . . . . . . . . .   6
   4.  Yeti DNS Testbed Infrastructure . . . . . . . . . . . . . . .   6
     4.1.  Root Zone Retrieval . . . . . . . . . . . . . . . . . . .   8
     4.2.  Transformation of Root Zone to Yeti-Root Zone . . . . . .   9
       4.2.1.  ZSK and KSK Key Sets Shared Between DMs . . . . . . .  10
       4.2.2.  Unique ZSK per DM; No Shared KSK  . . . . . . . . . .  10
       4.2.3.  Preserving Root Zone NSEC Chain and ZSK RRSIGs  . . .  11
     4.3.  Yeti-Root Zone Distribution . . . . . . . . . . . . . . .  12
     4.4.  Synchronization of Service Metadata . . . . . . . . . . .  12
     4.5.  Yeti-Root Server Naming Scheme  . . . . . . . . . . . . .  13
     4.6.  Yeti-Root Servers . . . . . . . . . . . . . . . . . . . .  14
     4.7.  Experimental Traffic  . . . . . . . . . . . . . . . . . .  16
     4.8.  Traffic Capture and Analysis  . . . . . . . . . . . . . .  16
   5.  Operational Experience with the Yeti DNS Testbed  . . . . . .  17
     5.1.  Viability of IPv6-Only Operation  . . . . . . . . . . . .  17
       5.1.1.  IPv6 Fragmentation  . . . . . . . . . . . . . . . . .  17
       5.1.2.  Serving IPv4-Only End-Users . . . . . . . . . . . . .  18

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     5.2.  Zone Distribution . . . . . . . . . . . . . . . . . . . .  19
       5.2.1.  Zone Transfers  . . . . . . . . . . . . . . . . . . .  19
       5.2.2.  Delays in Yeti-Root Zone Distribution . . . . . . . .  20
       5.2.3.  Mixed RRSIGs from different DM ZSKs . . . . . . . . .  20
     5.3.  DNSSEC KSK Rollover . . . . . . . . . . . . . . . . . . .  21
       5.3.1.  Failure-Case KSK Rollover . . . . . . . . . . . . . .  21
       5.3.2.  KSK Rollover vs. BIND9 Views  . . . . . . . . . . . .  22
       5.3.3.  Large Responses during KSK Rollover . . . . . . . . .  22
     5.4.  Capture of Large DNS Response . . . . . . . . . . . . . .  23
     5.5.  Automated Hints File Maintenance  . . . . . . . . . . . .  24
     5.6.  Root Label Compression in Knot DNS Server . . . . . . . .  25
   6.  Conclusions . . . . . . . . . . . . . . . . . . . . . . . . .  25
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  27
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  28
   9.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  28
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  28
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  28
     10.2.  Informative References . . . . . . . . . . . . . . . . .  29
     10.3.  URIs . . . . . . . . . . . . . . . . . . . . . . . . . .  32
   Appendix A.  Yeti-Root Hints File . . . . . . . . . . . . . . . .  33
   Appendix B.  Yeti-Root Server Priming Response  . . . . . . . . .  34
   Appendix C.  Active IPv6 Prefixes in Yeti DNS testbed . . . . . .  36
   Appendix D.  Tools developed for Yeti DNS testbed . . . . . . . .  36
   Appendix E.  Controversy  . . . . . . . . . . . . . . . . . . . .  37
   Appendix F.  About This Document  . . . . . . . . . . . . . . . .  38
     F.1.  Venue . . . . . . . . . . . . . . . . . . . . . . . . . .  38
     F.2.  Revision History  . . . . . . . . . . . . . . . . . . . .  38
       F.2.1.  draft-song-yeti-testbed-experience-00 through -03 . .  38
       F.2.2.  draft-song-yeti-testbed-experience-04 . . . . . . . .  38
       F.2.3.  draft-song-yeti-testbed-experience-05 . . . . . . . .  39
       F.2.4.  draft-song-yeti-testbed-experience-06 . . . . . . . .  39
       F.2.5.  draft-song-yeti-testbed-experience-07 . . . . . . . .  39
       F.2.6.  draft-song-yeti-testbed-experience-08 . . . . . . . .  39
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  39

1.  Introduction

   The Domain Name System (DNS), as originally specified in [RFC1034]
   and [RFC1035], has proved to be an enduring and important platform
   upon which almost every end-user of the Internet relies.  Despite its
   longevity, extensions to the protocol, new implementations and
   refinements to DNS operations continue to emerge both inside and
   outside the IETF.

   The Root Server System in particular has seen technical innovation
   and development, for example in the form of wide-scale anycast
   deployment, the mitigation of unwanted traffic on a global scale, the
   widespread deployment of Response Rate Limiting [RRL], the

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   introduction of IPv6 transport, the deployment of DNSSEC, changes in
   DNSSEC key sizes, and preparations to roll the root zone's Key
   Signing Key (KSK) and corresponding trust anchor.  These projects
   created tremendous qualitative operational change, and required
   impressive caution and study prior to implementation.  They took
   place in parallel with the quantitative expansion or delegations for
   new TLDs [1].

   Aspects of the operational structure of the Root Server System have
   been described in such documents as [TNO2009], [ISC-TN-2003-1],
   [RSSAC001] and [RFC7720].  Such references, considered together,
   provide sufficient insight into the operations of the system as a
   whole that it is straightforward to imagine structural changes to the
   root server system's infrastructure and to wonder what the
   operational implications of such changes might be.

   The Yeti DNS Project was conceived in May 2015 to provide a non-
   production testbed upon which the technical community could propose
   and run experiments designed to answer these kinds of questions.
   Coordination for the project was provided by TISF, the WIDE Project
   and the Beijing Internet Institute.  Many volunteers collaborated to
   build a distributed testbed that at the time of writing includes 25
   Yeti root servers with 16 operators and handles experimental traffic
   from individual volunteers, universities, DNS vendors and distributed
   measurement networks.

   By design, the Yeti testbed system serves the root zone published by
   the IANA with only those structural modifications necessary to ensure
   that it is able to function usefully in the Yeti testbed system
   instead of the production Root Server system.  In particular, no
   delegation for any top-level zone is changed, added or removed from
   the IANA-published root zone to construct the root zone served by the
   Yeti testbed system, and changes in the root zone are reflected in
   the testbed in near real-time.  In this document, for clarity, we
   refer to the zone derived from the IANA-published root zone as the
   Yeti-Root zone.

   The Yeti DNS testbed serves a similar function to the Root Server
   System in the sense that they both serve similar zones: the Yeti-Root
   zone and the IANA-published root zone.  However, the Yeti DNS testbed
   only serves clients that are explicitly configured to participate in
   the experiment, whereas the Root Server System serves the whole
   Internet.  Since the dependent end-users and systems of the Yeti DNS
   testbed are known and their operations well-coordinated with those of
   the Yeti project, it has been possible to deploy structural changes
   in the Yeti DNS testbed with effective measurement and analysis,
   something that is difficult or simply impractical in the production
   Root Server System.

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2.  Requirements Notation and Conventions

   Through the document, any mention to "Root" with an uppercase R and
   without other prefix, refers to the "IANA Root" systems used in the
   production Internet.  Proper mentions to the Yeti infrastructure will
   be prefixed with "Yeti", like "Yeti-Root Zone", "Yeti-DNS", and so

3.  Areas of Study

   Examples of topics that the Yeti DNS Testbed was built to address are
   included below, each illustrated with indicative questions.

3.1.  Implementation of a Root Server System-like Testbed

   o  How can a testbed be constructed and deployed on the Internet,
      allowing useful public participation without any risk of
      disruption of the Root Server System?

   o  How can representative traffic be introduced into such a testbed
      such that insights into the impact of specific differences between
      the testbed and the Root Server System can be observed?

3.2.  Yeti-Root Zone Distribution

   o  What are the scaling properties of Yeti-Root zone distribution as
      the number of Yeti-Root servers, Yeti-Root server instances or
      intermediate distribution points increase?

3.3.  Yeti-Root Server Names and Addressing

   o  What naming schemes other than those closely analogous to the use
      of ROOT-SERVERS.NET in the production root zone are practical, and
      what are their respective advantages and disadvantages?

   o  What are the risks and benefits of signing the zone that contains
      the names of the Yeti-Root servers?

   o  What automatic mechanisms might be useful to improve the rate at
      which clients of Yeti-Root servers are able to react to a Yeti-
      Root server renumbering event?

3.4.  IPv6-Only Yeti-Root Servers

   o  Are there negative operational effects in the use of IPv6-only
      Yeti-Root servers, compared to the use of servers that are dual-

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   o  What effect does the IPv6 fragmentation model have on the
      operation of Yeti-Root servers, compared with that of IPv4?

3.5.  DNSSEC in the Yeti-Root Zone

   o  Is it practical to sign the Yeti-Root zone using multiple,
      independently-operated DNSSEC signers and multiple corresponding
      Zone Signing Key(ZSK)?

   o  To what extent is [RFC5011]: "Automated Updates of DNS Security
      (DNSSEC) Trust Anchors" supported by resolvers?

   o  Does the KSK Rollover plan designed and in the process of being
      implemented by ICANN work as expected on the Yeti testbed?

   o  What is the operational impact of using much larger RSA key sizes
      in the ZSKs used in a root?

   o  What are the operational consequences of choosing DNSSEC
      algorithms other than RSA to sign a root?

4.  Yeti DNS Testbed Infrastructure

   The purpose of the testbed is to allow DNS queries from stub
   resolvers, mediated by recursive resolvers, to be delivered to Yeti-
   Root servers, and for corresponding responses generated on the Yeti-
   Root servers to be returned, as illustrated in Figure 1.

       ,----------.        ,-----------.        ,------------.
       |   stub   +------> | recursive +------> | Yeti-Root  |
       | resolver | <------+ resolver  | <------+ nameserver |
       `----------'        `-----------'        `------------'
          ^                   ^                    ^
          |  appropriate      |  Yeti-Root hints;  |  Yeti-Root zone
          `- resolver         `- Yeti-Root trust   `- with DNSKEY RRSet
             configured          anchor               signed by
                                                      Yeti-Root KSK

                  Figure 1: High-Level Testbed Components

   To use the Yeti DNS testbed, a recursive resolver must be configured
   to use the Yeti-Root servers.  That configuration consists of a list
   of names and addresses for the Yeti-Root servers (often referred to
   as a "hints file") that replaces the corresponding hints used for the
   production Root Server System (Appendix A).  If resolvers are
   configured to validate DNSSEC, then they also need to be configured

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   with a DNSSEC trust anchor that corresponds to a KSK used in the Yeti
   DNS Project, in place of the normal trust anchor set used for the
   Root Zone.

   Since the Yeti root(s) are signed with Yeti keys, rather than those
   used by the IANA root, corresponding changes are needed in the
   resolver trust anchors.  Corresponding changes are required in the
   Yeti-Root hints file Appendix A.  Those changes would be properly
   rejected by any validator using the production Root Server System's
   root zone trust anchor set as bogus.

   Stub resolvers become part of the Yeti DNS Testbed by their use of
   recursive resolvers that are configured as described above.

   The data flow from IANA to stub resolvers through the Yeti testbed is
   illustrated in Figure 2 and are described in more detail in the
   sections that follow.

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                             ,-- / IANA Root Zone / ---.
                             |  `----------------'     |
                             |            |            |
                             |            |            |       Root Zone
     ,--------------.    ,---V---.    ,---V---.    ,---V---.
     | Yeti Traffic |    | BII   |    | WIDE  |    | TISF  |
     | Collection   |    |  DM   |    |  DM   |    |  DM   |
     `----+----+----'    `---+---'    `---+---'    `---+---'
          |    |       ,-----'    ,-------'            `----.
          |    |       |          |                         |  Yeti-Root
          ^    ^       |          |                         |     Zone
          |    |   ,---V---.  ,---V---.                 ,---V---.
          |    `---+ Yeti  |  | Yeti  |  . . . . . . .  | Yeti  |
          |        | Root  |  | Root  |                 | Root  |
          |        `---+---'  `---+---'                 `---+---'
          |            |          |                         |    DNS
          |            |          |                         |  Response
          |         ,--V----------V-------------------------V--.
          `---------+              Yeti Resolvers              |
                                         |                       DNS
                                         |                     Response
                    |            Yeti Stub Resolvers           |

   The three coordinators of Yeti DNS testbed :
   BII : Beijing Internet Institute
   WIDE: Widely Integrated Distributed Environment Project
   TISF: A collaborative engineering and security project by Paul Vixie

                        Figure 2: Testbed Data Flow

   Note that the roots are not bound to Distribution Masters(DM).  DMs
   update their zone in a time schedule describe in Section 4.1 Each of
   DMs who update the latest zone can send notify to all roots.  So the
   zone transfer can happened between any DM and any root.

4.1.  Root Zone Retrieval

   The Yeti-Root Zone is distributed within the Yeti DNS testbed through
   a set of internal master servers that are referred to as Distribution
   Masters (DMs).  These server elements distribute the Yeti-Root zone
   to all Yeti-Root servers.  The means by which the Yeti DMs construct
   the Yeti-Root zone for distribution is described below.

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   Since Yeti DNS DMs do not receive DNS NOTIFY [RFC1996] messages from
   the Root Server System, a polling approach is used to determine when
   new revisions of the root zone are available from the production Root
   Server System.  Each Yeti DM requests the Root Zone Start of
   Authority(SOA) record from a Root server that permits unauthenticated
   zone transfers of the root zone, and performs a zone transfer from
   that server if the retrieved value of SOA.SERIAL is greater than that
   of the last retrieved zone.

   At the time of writing, unauthenticated zone transfers of the Root
   Zone are available directly from B-Root, C-Root, F-Root, G-Root and
   K-Root, and from L-Root via the two servers XFR.CJR.DNS.ICANN.ORG and
   XFR.LAX.DNS.ICANN.ORG, as well as via FTP from sites maintained by
   the Root Zone Maintainer and the IANA Functions Operator.  The Yeti
   DNS Testbed retrieves the Root Zone using zone transfers from F-Root.
   The schedule on which F-Root is polled by each Yeti DM is as follows:

                  | DM Operator | Time                  |
                  | BII         | UTC hour + 00 minutes |
                  | WIDE        | UTC hour + 20 minutes |
                  | TISF        | UTC hour + 40 minutes |

   The Yeti DNS testbed uses multiple DMs, each of which acts
   autonomously and equivalently to its siblings.  Any single DM can act
   to distribute new revisions of the Yeti-Root zone, and is also
   responsible for signing the RRSets that are changed as part of the
   transformation of the Root Zone into the Yeti-Root zone described in
   Section 4.2.  This multiple DM model intend to provide a basic
   structure to implement idea of shared zone control proposed in

4.2.  Transformation of Root Zone to Yeti-Root Zone

   Two distinct approaches have been deployed in the Yeti-DNS Testbed,
   separately, to transform the Root Zone into the Yeti-Root Zone.  At a
   high level both approaches are equivalent in the sense that they
   replace a minimal set of information in the root zone with
   corresponding data for the Yeti DNS Testbed; the mechanisms by which
   the transforms are executed are different, however.  Each is
   discussed in turn in Section 4.2.1 and Section 4.2.2, respectively.

   A third approach has also been proposed, but not yet implemented.
   The motivations and changes implied by that approach are described in
   Section 4.2.3.

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4.2.1.  ZSK and KSK Key Sets Shared Between DMs

   The approach described here was the first to be implemented.  It
   features entirely autonomous operation of each DM, but also requires
   secret key material (the private key in each of the Yeti-Root KSK and
   ZSK key-pairs) to be distributed and maintained on each DM in a
   coordinated way.

   The Root Zone is transformed as follows to produce the Yeti-Root
   Zone.  This transformation is carried out autonomously on each Yeti
   DNS Project DM.  Each DM carries an authentic copy of the current set
   of Yeti KSK and ZSK key pairs, synchronized between all DMs (see
   Section 4.4).

   1.  SOA.MNAME is set to

   2.  SOA.RNAME is set to <dm-operator>  where <dm-
       operator> is currently one of "wide", "bii" or "tisf".

   3.  All DNSKEY, RRSIG and NSEC records are removed.

   4.  The apex Name Server(NS) RRSet is removed, with the corresponding
       root server glue (A and AAAA) RRSets.

   5.  A Yeti DNSKEY RRSet is added to the apex, comprising the public
       parts of all Yeti KSK and ZSKs.

   6.  A Yeti NS RRSet is added to the apex that includes all Yeti-Root

   7.  Glue records (AAAA only, since Yeti-Root servers are v6-only) for
       all Yeti-Root servers are added.

   8.  The Yeti-Root Zone is signed: the NSEC chain is regenerated; the
       Yeti KSK is used to sign the DNSKEY RRSet, and the shared ZSK is
       used to sign every other RRSet.

   Note that the SOA.SERIAL value published in the Yeti-Root Zone is
   identical to that found in the root zone.

4.2.2.  Unique ZSK per DM; No Shared KSK

   The approach described here was the second to be implemented and
   maintained as stable state.  Each DM is provisioned with its own,
   dedicated ZSK key pairs that are not shared with other DMs.  A Yeti-
   Root DNSKEY RRSet is constructed and signed upstream of all DMs as
   the union of the set of active Yeti-Root KSKs and the set of active
   ZSKs for every individual DM.  Each DM now only requires the secret

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   part of its own dedicated ZSK key pairs to be available locally, and
   no other secret key material is shared.  The high-level approach is
   illustrated in Figure 3.

                            ,----------.         ,-----------.
                   .--------> BII ZSK  +---------> Yeti-Root |
                   | signs  `----------'  signs  `-----------'
     ,-----------. |        ,----------.         ,-----------.
     | Yeti KSK  +-+--------> TISF ZSK +---------> Yeti-Root |
     `-----------' | signs  `----------'  signs  `-----------'
                   |        ,----------.         ,-----------.
                   `--------> WIDE ZSK +---------> Yeti-Root |
                     signs  `----------'  signs  `-----------'

                        Figure 3: Unique ZSK per DM

   The process of retrieving the Root Zone from the Root Server System
   and replacing and signing the apex DNSKEY RRSet no longer takes place
   on the DMs, and instead takes place on a central Hidden Master.  The
   production of signed DNSKEY RRSets is analogous to the use of Signed
   Key Responses (SKR) produced during ICANN KSK key ceremonies

   Each DM now retrieves source data (with pre-modified and Yeti-signed
   DNSKEY RRset, but otherwise unchanged) from the Yeti DNS Hidden
   Master instead of from the Root Server System.

   Each DM carries out a similar transformation to that described in
   Section 4.2.1, except that DMs no longer need to modify or sign the
   DNSKEY RRSet, and the DM's unique local ZSK is used to sign every
   other RRset.

4.2.3.  Preserving Root Zone NSEC Chain and ZSK RRSIGs

   A change to the transformation described in Section 4.2.2 has been
   proposed as a Yeti experiment called PINZ [2]which would preserve the
   NSEC chain from the Root Zone and all RRSIG RRs generated using the
   Root Zone's ZSKs.  The DNSKEY RRSet would continue to be modified to
   replace the Root Zone KSKs, but Root Zone ZSKs will be kept intact,
   and the Yeti KSK would be used to generate replacement signatures
   over the apex DNSKEY and NS RRSets.  Source data would continue to
   flow from the Root Server System through the Hidden Master to the set
   of DMs, but no DNSSEC operations would be required on the DMs and the
   source NSEC and most RRSIGs would remain intact.

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   This approach has been suggested in order to keep minimal changes
   from IANA root zone and provide cryptographically-verifiable
   confidence that no owner name in the root zone had been changed in
   the process of producing the Yeti-Root zone from the Root Zone,
   addressing one of the concerns described in Appendix E in a way that
   can be verified automatically.

4.3.  Yeti-Root Zone Distribution

   Each Yeti DM is configured with a full list of Yeti-Root Server
   addresses to send NOTIFY [RFC1996] messages to, which also forms the
   basis for an address-based access-control list for zone transfers.
   Authentication by address could be replaced with more rigorous
   mechanisms (e.g. using Transaction Signatures (TSIG) [RFC2845]); this
   has not been done at the time of writing since the use of address-
   based controls avoids the need for the distribution of shared secrets
   amongst the Yeti-Root Server Operators.

   Individual Yeti-Root Servers are configured with a full set of Yeti
   DM addresses to which SOA and Authoritative Transfer (AXFR) queries
   may be sent in the conventional manner.

4.4.  Synchronization of Service Metadata

   Changes in the Yeti-DNS Testbed infrastructure such as the addition
   or removal of Yeti-Root servers, renumbering Yeti-Root Servers or
   DNSSEC key rollovers require coordinated changes to take place on all
   DMs.  The Yeti-DNS Testbed is subject to more frequent changes than
   are observed in the Root Server System and includes substantially
   more Yeti-Root Servers than there are IANA Root Servers, and hence a
   manual change process in the Yeti Testbed would be more likely to
   suffer from human error.  An automated and cooperated process was
   consequently implemented.

   The theory of this operation is that each DM operator runs a Git
   repository locally, containing all service metadata involved in the
   operation of each DM.  When a change is desired and approved among
   all Yeti coordinators, one DM operator (usually BII) updates the
   local Git repository.  A serial number in the future (in two days) is
   chosen for when the changes become active.  The DM operator then
   pushes the changes to the Git repositories of the other two DM
   operators who have chance to check and edit the repo.  When the
   serial of the root zone passes the number chosen, then changes were
   pulled automatically to individual DMs and promoted to production.

   The three Git repositories are synchronized by configuring them as
   remote servers.  For example at BII we push to all three DM's repo as

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             $ git remote -v
             origin (fetch)
             origin (push)
             origin (push)
             origin (push)

                                 Figure 4

   More detailed information of DM Synchronization, please find the [3] document in Yeti's GitHub repo.

4.5.  Yeti-Root Server Naming Scheme

   The current naming scheme for Root Servers was normalized to use
   single-character host names (A through M) under the domain ROOT-
   SERVERS.NET, as described in [RSSAC023].  The principal benefit of
   this naming scheme was that DNS label compression could be used to
   produce a priming response that would fit within 512 bytes at the
   time it was introduced, 512 bytes being the maximum DNS message size
   using UDP transport without EDNS(0) [RFC6891].

   Yeti-Root Servers do not use this optimization, but rather use free-
   form nameserver names chosen by their respective operators -- in
   other words, no attempt is made to minimize the size of the priming
   response through the use of label compression.  This approach aims to
   challenge the need for a minimally-sized priming response in a modern
   DNS ecosystem where EDNS(0) is prevalent.

   Priming responses from Yeti-Root Servers do not always include server
   addresses in the additional section, as is the case with priming
   responses from Root Servers.  In particular, Yeti-Root Servers
   running BIND9 return an empty additional section if the configuration
   parameter minimum-responses is set, forcing resolvers to complete the
   priming process with a set of conventional recursive lookups in order
   to resolve addresses for each Yeti-Root server.  The Yeti-Root
   Servers running NSD were observed to return a fully-populated
   additional section (depending of course of the EDNS buffer size in

   Various approaches to normalize the composition of the priming
   response were considered, including:

   o  Require use of DNS implementations that exhibit a desired
      behaviour in the priming response;

   o  Modify nameserver software or configuration as used by Yeti-Root

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   o  Isolate the names of Yeti-Root Servers in one or more zones that
      could be slaved on each Yeti-Root Server, renaming servers as
      necessary, giving each a source of authoritative data with which
      the authority section of a priming response could be fully
      populated.  This is the approach used in the Root Server System
      with the ROOT-SERVERS.NET zone.

   The potential mitigation of renaming all Yeti-Root Servers using a
   scheme that would allow their names to exist directly in the root
   zone was not considered, since that approach implies the invention of
   new top-level labels not present in the Root Zone.

   Given the relative infrequency of priming queries by individual
   resolvers and the additional complexity or other compromises implied
   by each of those mitigations, the decision was made to make no effort
   to ensure that the composition of priming responses was identical
   across servers.  Even the empty additional sections generated by
   Yeti-Root Servers running BIND9 seem to be sufficient for all
   resolver software tested; resolvers simply perform a new recursive
   lookup for each authoritative server name they need to resolve.

4.6.  Yeti-Root Servers

   Various volunteers have donated authoritative servers to act as Yeti-
   Root servers.  At the time of writing there are 25 Yeti-Root servers
   distributed globally, one of which is named using an IDNA2008
   [RFC5890] label, shown in the following list in punycode.

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   | Name                                | Operator      | Location    |
   |                     | BII           | CHINA       |
   |                    | TSIF          | USA         |
   |                  | WIDE Project  | Japan       |
   |                 | as59715       | Italy       |
   |                   | Dahu Group    | France      |
   |                  | Bond Internet | Spain       |
   |                                     | Systems       |             |
   |                       | Russia        | MSK-IX      |
   |                   | CERT Austria  | Austria     |
   |                  | ERNET India   | India       |
   |          | dnsworkshop   | Germany     |
   |                                     | /informnis    |             |
   |                   | Dahu Group    | France      |
   |                    | Aqua Ray SAS  | France      |
   |                   | SWITCH        | Switzerland |
   |                  | NIC Chile     | Chile       |
   |                | BII           | China       |
   |                | BII           | China       |
   |                | BII           | China       |
   |             | Yeti-ZA       | South       |
   |                                     |               | Africa      |
   |             | Yeti-AU       | Australia   |
   |                 | ERNET India   | India       |
   | xn--r2bi1c.xn--h2bv6c0a.xn--h2brj9c | ERNET India   | India       |
   |          | dnsworkshop   | USA         |
   |                                     | /informnis    |             |
   |                    | Monshouwer    | Netherlands |
   |                                     | Internet      |             |
   |                                     | Diensten      |             |
   |                   | DATEV         | Germany     |
   |                   | jhcloos       | USA         |

   The current list of Yeti-Root server is made available to a
   participating resolver first using a substitute hints file Appendix A
   and subsequently by the usual resolver priming process [RFC8109].
   All Yeti-Root servers are IPv6-only, foreshadowing a future IPv6-only
   Internet, and hence the Yeti-Root hints file contains no IPv4
   addresses and the Yeti-Root zone contains no IPv4 glues.  Note that
   the rationale of an IPv6-only testbed is to test whether IPv6-only
   root can survive any problem or impact when IPv4 is turned off, much
   like the context of IETF sunset4 WG [4].

   At the time of writing, all root servers within the Root Server
   System serve the ROOT-SERVERS.NET zone in addition to the root zone,

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   and all but one also serve the ARPA zone.  Yeti-Root servers serve
   the Yeti-Root zone only.

   Significant software diversity exists across the set of Yeti-Root
   servers, as reported by their volunteer operators at the time of

   o  Platform: 18 of 25 Yeti-Root servers are implemented on a Virtual
      Private Server(VPS) rather than bare metal.

   o  Operating System: 15 Yeti-Root servers run on Linux (Ubuntu,
      Debian, CentOS, Red Hat and ArchLinux); 4 run on FreeBSD, 1 on
      NetBSD and 1 in Windows server 2016.

   o  DNS software: 18 of 25 Yeti-Root servers use BIND9 (versions
      varying between 9.9.7 and 9.10.3); 4 use NSD (4.10 and 4.15); 2
      use Knot (2.0.1 and 2.1.0), 1 uses Bundy (1.2.0) and 1 uses MS DNS

4.7.  Experimental Traffic

   For the Yeti DNS Testbed to be useful as a platform for
   experimentation, it needs to carry statistically representative
   traffic.  Several approaches have been taken to load the system with
   traffic, including both real-world traffic triggered by end-users and
   synthetic traffic.

   Resolvers that have been explicitly configured to participate in the
   testbed, as described in Section 4, are a source of real-world, end-
   user traffic.  Due to efficient cache mechanism, the mean query rate
   is less than 100 qps in Yeti testbed, but a variety of sources are
   observed active in past one year, as summarized inAppendix C.

   Synthetic traffic has been introduced to the system from time to time
   in order to increase traffic loads.  Approaches include the use of
   distributed measurement platforms such as RIPE ATLAS to send DNS
   queries to Yeti-Root servers, and the capture of traffic sent from
   non-Yeti resolvers to the Root Server System which was subsequently
   modified and replayed towards Yeti-Root servers.

4.8.  Traffic Capture and Analysis

   Query and response traffic capture is available in the testbed in
   both Yeti resolvers and Yeti-Root servers in anticipation of
   experiments that require packet-level visibility into DNS traffic.

   Traffic capture is performed on Yeti-Root servers using either dnscap
   [5] or pcapdump (part of the pcaputils Debian package [6], with a

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   patch to facilitate triggered file upload [7].  PCAP-format files
   containing packet captures are uploaded using rsync to central

5.  Operational Experience with the Yeti DNS Testbed

   The following sections provide commentary on the operation and impact
   analyses of the Yeti-DNS Testbed described in Section 4.  More
   detailed descriptions of observed phenomena are available in Yeti DNS
   mailing list archives [8] and on the Yeti DNS blog [9].

5.1.  Viability of IPv6-Only Operation

   All Yeti-Root servers were deployed with IPv6 connectivity, and no
   IPv4 addresses for any Yeti-Root server were made available (e.g. in
   the Yeti hints file, or in the DNS itself).  This implementation
   decision constrained the Yeti-Root system to be v6-only.

   DNS implementations are generally adept at using both IPv4 and IPv6
   when both are available.  Servers that cannot be reliably reached
   over one protocol might be better queried over the other, to the
   benefit of end-users in the common case where DNS resolution is on
   the critical path for end-users' perception of performance.  However,
   this optimisation also means that systemic problems with one protocol
   can be masked by the other.  By forcing all traffic to be carried
   over IPv6, the Yeti DNS testbed aimed to expose any such problems and
   make them easier to identify and understand.  Several examples of
   IPv6-specific phenomena observed during the operation of the testbed
   are described in the sections that follow.

   Although the Yeti-Root servers themselves were only reachable using
   IPv6, real-world end-users often have no IPv6 connectivity.  The
   testbed was also able to explore the degree to which IPv6-only Yeti-
   Root servers were able to serve single-stack, IPv4-only end-user
   populations through the use of dual-stack Yeti resolvers.

5.1.1.  IPv6 Fragmentation

   In the Root Server System, structural changes with the potential to
   increase response sizes (and hence fragmentation, fallback to TCP
   transport or both) have been exercised with great care, since the
   impact on clients has been difficult to predict or measure.  The Yeti
   DNS Testbed is experimental and has the luxury of a known client
   base, making it far easier to make such changes and measure their

   Many of the experimental design choices described in this document
   were expected to trigger larger responses.  For example, the choice

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   of naming scheme for Yeti-Root Servers described in Section 4.5
   defeats label compression.  It makes a large priming response (up to
   1754 octets with 25 NS server and their glue) ; the Yeti-Root zone
   transformation approach described in Section 4.2.2 greatly enlarges
   the apex DNSKEY RRSet especially during the KSK rollover (up to 1975
   octets with 3 ZSK and 2 KSK).  An increased incidence of
   fragmentation was therefore expected.

   The Yeti-DNS Testbed provides service on IPv6 only.  However
   middlebox like firewall, and some routers are not friendly on IPv6
   fragments.  It is reported there is notable packets drop rate due to
   the mistreatment of middle-box on IPv6 fragment
   [I-D.taylor-v6ops-fragdrop] [RFC7872].  One APNIC study
   [IPv6-frag-DNS] reported that 37% of endpoints using IPv6-capable DNS
   resolver cannot receive a fragmented IPv6 response over UDP.

   To study the impact, RIPE Atlas probes were used.  For each Yeti-Root
   server, an Atlas measurement was setup using 100 IPv6-enabled probes
   from five regions, sending a DNS query for ./IN/DNSKEY using UDP
   transport with DO=1.  This measurement, when carried out concurrently
   with a Yeti KSK rollover, further exacerbating the potential for
   fragmentation, identified a 7% failure rate compared with a non-
   fragmented control.  A failure rate of 2% was observed with response
   sizes of 1414 octets, which was surprising given the expected
   prevalence of 1500-octet (Ethernet-framed) MTUs.

   The consequences of fragmentation were not limited to failures in
   delivering DNS responses over UDP transport.  There were two cases
   where a Yeti-Root server failed to transfer the Yeti-Root zone from a
   DM using TCP.  DM log files revealed "socket is not connected" errors
   corresponding to zone transfer requests.  Further experimentation
   revealed that combinations of NetBSD 6.1, NetBSD 7.0RC1, FreeBSD
   10.0, Debian 3.2 and VMWare ESXI 5.5 resulted in a high TCP MSS value
   of 1440 octets being negotiated between client and server despite the
   presence of the IPV6_USE_MIN_MTU socket option, as described in
   [I-D.andrews-tcp-and-ipv6-use-minmtu].  The mismatch appears to cause
   outbound segments greater in size than 1280 octets to be dropped
   before sending.  Setting the local TCP MSS to 1220 octets (chosen as
   1280-60, the size of the IPv6/TCP header with no other extension
   headers) was observed to be a pragmatic mitigation.

5.1.2.  Serving IPv4-Only End-Users

   Yeti resolvers have been successfully used by real-world end-users
   for general name resolution within a number of participant
   organisations, including resolution of names to IPv4 addresses and
   resolution by IPv4-only end-user devices.

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   Some participants, recognising the operational importance of
   reliability in resolver infrastructure and concerned about the
   stability of their IPv6 connectivity, chose to deploy Yeti resolvers
   in parallel to conventional resolvers, making both available to end-
   users.  While the viability of this approach provides a useful data
   point, end-users using Yeti resolvers exclusively provided a better
   opportunity to identify and understand any failures in the Yeti DNS
   testbed infrastructure.

   Resolvers deployed in IPv4-only environments were able to join the
   Yeti DNS testbed by way of upstream, dual-stack Yeti resolvers, or in
   one case, in CERNET2, by assigning IPv4 addresses to Yeti-Root
   servers and mapping them in dual-stack IVI translation devices

5.2.  Zone Distribution

   The Yeti DNS testbed makes use of multiple DMs to distribute the
   Yeti-Root zone, an approach that would allow the number of Yeti-Root
   servers to scale to a higher number than could be supported by a
   single distribution source and which provided redundancy.  The use of
   multiple DMs introduced some operational challenges, however, which
   are described in the following sections.

5.2.1.  Zone Transfers

   Yeti-Root Servers were configured to serve the Yeti-Root zone as
   slaves.  Each slave had all DMs configured as masters, providing
   redundancy in zone synchronisation.

   Each DM in the Yeti testbed served a Yeti-Root zone which is
   functionally equivalent but not congruent to that served by every
   other DM (see Section 4.3).  The differences included variations in
   the SOA.MNAME field and, more critically, in the RRSIGs for
   everything other than the apex DNSKEY RRSet, since signatures for all
   other RRSets are generated using a private key that is only available
   to the DM serving its particular variant of the zone (see
   Section 4.2, Section 4.2.2).

   Incremental Zone Transfer (IXFR), as described in [RFC1995], is a
   viable mechanism to use for zone synchronization between any Yeti-
   Root server and a consistent, single DM.  However, if that Yeti-Root
   server ever selected a different DM, IXFR would no longer be a safe
   mechanism; structural changes between the incongruent zones on
   different DMs would not be included in any transferred delta and the
   result would be a zone that was not internally self-consistent.  For
   this reason the first transfer after a change of DM would require
   AXFR, not IXFR.

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   None of the DNS software in use on Yeti-Root Servers supports this
   mixture of IXFR/AXFR according to the master server in use.  This is
   unsurprising, given that the environment described above in the Yeti-
   Root system is idiosyncratic; conventional zone transfer graphs
   involve zones that are congruent between all nodes.  For this reason,
   all Yeti-Root servers are configured to use AXFR at all times, and
   never IXFR, to ensure that zones being served are internally self-

5.2.2.  Delays in Yeti-Root Zone Distribution

   Each Yeti DM polled the Root Server System for a new revision of the
   root zone on an interleaved schedule, as described in Section 4.1.
   Consequently, different DMs were expected to retrieve each revision
   of the root zone, and make a corresponding revision of the Yeti-Root
   zone available, at different times.  The availability of a new
   revision of the Yeti-Root zone on the first DM would typically
   precede that of the last by 40 minutes.

   It might be expected given this distribution mechanism that the
   maximum latency between the publication of a new revision of the root
   zone and the availability of the corresponding Yeti-Root zone on any
   Yeti-Root server would be 20 minutes, since in normal operation at
   least one DM should serve that Yeti-Zone within 20 minutes of root
   zone publication.  In practice, this was not observed.

   In one case a Yeti-Root server running Bundy 1.2.0 on FreeBSD
   10.2-RELEASE was found to lag root zone publication by as much as ten
   hours, which upon investigation was due to software defects that were
   subsequently corrected.

   More generally, Yeti-Root servers were observed routinely to lag root
   zone publication by more than 20 minutes, and relatively often by
   more than 40 minutes.  Whilst in some cases this might be assumed to
   be a result of connectivity problems, perhaps suppressing the
   delivery of NOTIFY messages, it was also observed that Yeti-Root
   servers receiving a NOTIFY from one DM would often send SOA queries
   and AXFR requests to a different DM.  If that DM was not yet serving
   the new revision of the Yeti-Root zone, a delay in updating the Yeti-
   Root server would naturally result.

5.2.3.  Mixed RRSIGs from different DM ZSKs

   The second approach doing the transformation of Root Zone to Yeti-
   Root Zone (Section 4.2.2) introduce a situation that mixed RRSIGs
   from different DM ZSKs will be cached in one resolver.

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   It is observed that the Yeti-Root Zone served by any particular Yeti-
   Root Server will include signatures generated using the ZSK from the
   DM that served the Yeti-Root Zone to that Yeti-Root Server.
   Signatures cached at resolvers might be retrieved from any Yeti-Root
   Server, and hence are expected to be a mixture of signatures
   generated by different ZSKs.  Since all ZSKs can be trusted through
   the signature by the Yeti KSK over the DNSKEY RRSet, which includes
   all ZSKs, the mixture of signatures was predicted not to be a threat
   to reliable validation.

   It was first tested in BII's lab environment as a proof of concept.
   It is observed in resolver's DNSSEC log that the process of verifying
   rdataset show "success" with a key (keyid) in DNSKEY RRSet.  It was
   implemented later in three DMs which was carefully coordinated and
   made public to all Yeti resolver operators and participants in Yeti's
   mailing list.  At least 45 Yeti resolvers (deployed by Yeti
   operators) were under monitoring and set reporting trigger if
   anything wrong.  In addition, Yeti mailing list is open for error
   reports from other participants.  So far Yeti testbed has been
   operated in this configuration (with multiple ZSKs) for 2 years.  It
   is proved that this configuration is workable and reliable, even when
   individual ZSKs are rolled on different schedules.

   Another consequence of this approach is that the apex DNSKEY RRSet in
   the Yeti-Root zone is much larger than the corresponding DNSKEY RRSet
   in the Root Zone.  This requires more space and produce larger
   response to the query for DNSKEY RRset especially during the KSK

5.3.  DNSSEC KSK Rollover

   At the time of writing, the Root Zone KSK is expected to undergo a
   carefully-orchestrated rollover as described in [ICANN2016].  ICANN
   has commissioned various tests and has published an external test
   plan [ICANN2017].

   Three related DNSSEC KSK rollover exercises were carried out on the
   Yeti DNS testbed, somewhat concurrent with the planning and execution
   of the rollover in the root zone.  Brief descriptions of these
   exercises are included below.

5.3.1.  Failure-Case KSK Rollover

   The first KSK rollover that was executed on the Yeti DNS testbed
   deliberately ignored the 30-day hold-down timer specified in
   [RFC5011] before retiring the outgoing KSK.

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   It was confirmed that clients of some (but not all) validating Yeti
   resolvers experienced resolution failures (received SERVFAIL
   responses) following this change.  Those resolvers required
   administrator intervention to install a functional trust anchor
   before resolution was restored.

5.3.2.  KSK Rollover vs. BIND9 Views

   The second Yeti KSK rollover was designed with similar phases to the
   ICANN's KSK rollover roll, although with modified timings to reduce
   the time required to complete the process.  The "slot" used in this
   rollover was ten days long, as follows:

                  |              | 19444    | New Key  |
                  | slot 1       | pub+sign |          |
                  | slot 2,3,4,5 | pub+sign | pub      |
                  | slot 6,7     | pub      | pub+sign |
                  | slot 8       | revoke   | pub+sign |
                  | slot 9       |          | pub+sign |

   During this rollover exercise, a problem was observed on one Yeti
   resolver that was running BIND 9.10.4-p2 [KROLL-ISSUE].  That
   resolver was configured with multiple views serving clients in
   different subnets at the time that the KSK rollover began.  DNSSEC
   validation failures were observed following the completion of the KSK
   rollover, triggered by the addition of a new view, intended to serve
   clients from a new subnet.

   BIND 9.10 requires "managed-keys" configuration to be specified in
   every view, a detail that was apparently not obvious to the operator
   in this case and which was subsequently highlighted by ISC in their
   general advice relating to KSK rollover in the root zone to users of
   BIND 9 [10].  When the "managed-keys" configuration is present in
   every view that is configured to perform validation, trust anchors
   for all views are updated during a KSK rollover.

5.3.3.  Large Responses during KSK Rollover

   Since a KSK rollover necessarily involves the publication of outgoing
   and incoming public keys simultaneously, an increase in the size of
   DNSKEY responses is expected.  The third KSK rollover carried out on
   the Yeti DNS testbed was accompanied by a concerted effort to observe
   response sizes and their impact on end-users.

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   As described in Section 4.2.2, in the Yeti DNS testbed each DM can
   maintain control of its own set of ZSKs, which can undergo rollover
   independently.  During a KSK rollover where concurrent ZSK rollovers
   are executed by each of three DMs the maximum number of apex DNSKEY
   RRs present is eight (incoming and outcoming KSK, plus incoming and
   outgoing of each of three ZSKs).  In practice, however, such
   concurrency did not occur; only the BII ZSK was rolled during the KSK
   rollover, and hence only three DNSKEY RRSet configurations were

   o  3 ZSK and 2 KSK, DNSKEY response of 1975 octets;

   o  3 ZSK and 1 KSK, DNSKEY response of 1414 octets; and

   o  2 ZSK and 1 KSK, DNSKEY response of 1139 octets.

   RIPE Atlas probes were used as described in Section 5.1.1 to send
   DNSKEY queries directly to Yeti-Root servers.  The numbers of queries
   and failures were recorded and categorized according to the response
   sizes at the time the queries were sent.  A summary of the results
   ([YetiLR]) is as follows:

        | Response Size | Failures | Total Queries | Failure rate |
        | 1139          | 274      | 64252         | 0.0042       |
        | 1414          | 3141     | 126951        | 0.0247       |
        | 1975          | 2920     | 42529         | 0.0687       |

   The general approach illustrated briefly here provides a useful
   example of how the design of the Yeti DNS testbed, separate from the
   Root Server System but constructed as a live testbed on the Internet,
   facilitates the use of general-purpose active measurement facilities
   such as RIPE Atlas probes as well as internal passive measurement
   such as packet capture.

5.4.  Capture of Large DNS Response

   Packet capture is a common approach in production DNS systems where
   operators require fine-grained insight into traffic in order to
   understand production traffic.  For authoritative servers, capture of
   inbound query traffic is often sufficient, since responses can be
   synthesized with knowledge of the zones being served at the time the
   query was received.  Queries are generally small enough not to be
   fragmented, and even with TCP transport are generally packed within a
   single segment.

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   The Yeti DNS testbed has different requirements; in particular there
   is a desire to compare responses obtained from the Yeti
   infrastructure with those received from the Root Server System in
   response to a single query stream (e.g. using YmmV as described in
   Appendix D).  Some Yeti-Root servers were capable of recovering
   complete DNS messages from within nameservers, e.g. using dnstap;
   however, not all servers provided that functionality and a consistent
   approach was desirable.

   The requirement passive capture of responses from the wire together
   with experiments that were expected (and in some cases designed) to
   trigger fragmentation and use of TCP transport led to the development
   of a new tool, PcapParser, to perform fragment and TCP stream
   reassembly from raw packet capture data.  A brief description of
   PcapParser is included in Appendix D.

5.5.  Automated Hints File Maintenance

   Renumbering events in the Root Server System are relatively rare.
   Although each such event is accompanied by the publication of an
   updated hints file in standard locations, the task of updating local
   copies of that file used by DNS resolvers is manual, and the process
   has an observably-long tail: for example, in 2015 J-Root was still
   receiving traffic at its old address some thirteen years after
   renumbering [Wessels2015].

   The observed impact of these old, deployed hints file is minimal,
   likely due to the very low frequency of such renumbering events.
   Even the oldest of hints file would still contain some accurate root
   server addresses from which priming responses could be obtained.

   By contrast, due to the experimental nature of the system and the
   fact that it is operated mainly by volunteers, Yeti-Root Servers are
   added, removed and renumbered with much greater frequency.  A tool to
   facilitate automatic maintenance of hints files was therefore
   created, [hintUpdate].

   The automated procedure followed by the hintUpdate tool is as

   1.  Use the local resolver to obtain a response to the query ./IN/NS;

   2.  Use the local resolver to obtain a set of IPv4 and IPv6 addresses
       for each name server;

   3.  Validate all signatures obtained from the local resolvers, and
       confirm that all data is signed;

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   4.  Compare the data obtained to that contained within the currently-
       active hints file; if there are differences, rotate the old one
       away and replace it with a new one.

   This tool would not function unmodified when used in the Root Server
   System, since the names of individual Root Servers (e.g.  A.ROOT-
   SERVERS.NET) are not DNSSEC signed.  All Yeti-Root Server names are
   DNSSEC signed, however, and hence this tool functions as expected in
   that environment.

5.6.  Root Label Compression in Knot DNS Server

   [RFC1035] specifies that domain names can be compressed when encoded
   in DNS messages, being represented as one of

   1.  a sequence of labels ending in a zero octet;

   2.  a pointer; or

   3.  a sequence of labels ending with a pointer.

   The purpose of this flexibility is to reduce the size of domain names
   encoded in DNS messages.

   It was observed that Yeti-Root Servers running Knot 2.0 would
   compress the zero-length label (the root domain, often represented as
   ".") using a pointer to an earlier example.  Although legal, this
   encoding increases the encoded size of the root label from one octet
   to two; it was also found to break some client software, in
   particular the Go DNS library.  Bug reports were filed against both
   Knot and the Go DNS library, and both were resolved in subsequent

6.  Conclusions

   Yeti DNS was designed and implemented as a live DNS root system
   testbed.  It serves a root zone ("Yeti-Root" in this document)
   derived from the root zone root zone published by the IANA with only
   those structural modifications necessary to ensure its function in
   the testbed system.  The Yeti DNS testbed has proven to be a useful
   platform to address many questions that would be challenging to
   answer using the production Root Server System, such as those
   included in Section 3.

   Indicative findings following from the construction and operation of
   the Yeti DNS testbed include:

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   o  Operation in a pure IPv6-only environment; confirmation of a
      significant failure rate in the transmission of large responses
      (~7%), but no other persistent failures observed.  Two cases in
      which Yeti-Root servers failed to retrieve the Yeti-Root zone due
      to fragmentation of TCP segments; mitigated by setting a TCP MSS
      of 1220 octets (see Section 5.1.1).

   o  Successful operation with three autonomous Yeti-Root zone signers
      and 25 Yeti-Root servers, and confirmation that IXFR is not an
      appropriate transfer mechanism of zones that are structurally
      incongruent across different transfer paths (see Section 5.2).

   o  ZSK size increased to 2048 bits and multiple KSK rollovers
      executed to exercise RFC 5011 support in validating resolvers;
      identification of pitfalls relating to views in BIND9 when
      configured with "managed-keys" (see Section 5.3).

   o  Use of natural (non-normalized) names for Yeti-Root servers
      exposed some differences between implementations in the inclusion
      of additional-section glue in responses to priming queries;
      however, despite this inefficiency, Yeti resolvers were observed
      to function adequately (see Section 4.5).

   o  It was observed that Knot 2.0 performed label compression on the
      root (empty) label.  This results in an increased encoding size
      for references to the root label, since a pointer is encoded as
      two octets whilst the root label itself only requires one (see
      Section 5.6).

   o  Some tools were developed in response to the operational
      experience of running and using the Yeti DNS testbed: DNS fragment
      and DNS Additional Truncated Response (ATR) for large DNS
      responses, a BIND9 patch for additional section glue, YmmV and
      IPv6 defrag for capturing and mirroring traffic.  In addition a
      tool to facilitate automatic maintenance of hints files was
      created (see Appendix D).

   The Yeti DNS testbed was used only by end-users whose local
   infrastructure providers had made the conscious decision to do so, as
   is appropriate for an experimental, non-production system.  So far no
   serious user complains reached Yeti's mailing list during Yeti normal
   operation.  Although adding more instances into Yeti root system may
   help to better enhance the quality of service, but it is generally
   accepted that Yeti DNS performance is good enough to serve the
   purpose of DNS Root testbed.

   The experience gained during the operation of the Yeti DNS testbed
   suggested several topics worthy of further study:

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   o  Priming Truncation and TCP-only Yeti-Root servers: observe and
      measure the worst-possible case for priming truncation by
      responding with TC=1 to all priming queries received over UDP
      transport, forcing clients to retry using TCP.  This should also
      give some insight into the usefulness of TCP-only DNS in general.

   o  KSK ECDSA Rollover: one possible way to reduce DNSKEY response
      sizes is to change to an elliptic curve signing algorithm.  While
      in principle this can be done separately for the KSK and the ZSK,
      the RIPE NCC has done research recently and discovered that some
      resolvers require that both KSK and ZSK use the same algorithm.
      This means that an algorithm roll also involves a KSK roll.
      Performing an algorithm roll at the root would be an interesting

   o  Sticky Notify for zone transfer: the non-applicability of IXFR as
      a zone transfer mechanism in the Yeti DNS testbed could be
      mitigated by the implementation of a sticky preference for master
      server for each slave, such that an initial AXFR response could be
      followed up with IXFR requests without compromising zone integrity
      in the case (as with Yeti) that equivalent but incongruent
      versions of a zone are served by different masters.

   o  Key distribution for zone transfer credentials: the use of a
      shared secret between slave and master requires key distribution
      and management whose scaling properties are not ideally suited to
      systems with large numbers of transfer clients.  Other approaches
      for key distribution and authentication could be considered.

   o  In section 3.12 of [RFC8324], a "Centrally Controlled Root" is
      viewed as a issue of DNS.  It is interesting in future study to
      try and test some technical tools like blockchain [11] to to
      remove the technical requirement for a central authority over the

7.  Security Considerations

   As introduced in Section 4.4,service metadata is synchronized among 3
   DMs using Git tool.  Any security issue around Git may affect Yeti DM
   operation.  For example, hacker may compromise one DM's git
   repository and push unwanted changes to Yeti DM system which may
   introduce a bad root server or bad key for a period of time.

   Yeti resolver needs the bootstrapping files to join the testbed, like
   hint file and trust anchor of Yeti.  All required information is
   published in and  If hacker tampers those
   websites with a fake page, new resolver may lose its way and
   configured with a bad root.

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   DNSSEC is an important research goal in Yeti DNS testbed.  To reduce
   the central function of DNSSEC for Root zone, we sign the Yeti-Root
   zone using multiple, independently-operated DNSSEC signers and
   multiple corresponding ZSKs (see Section 4.2).  To verify ICANN's KSK
   rollover, we rolled the Yeti KSK three times according to RFC5011 and
   do have some observations(see Section 5.3).  In addition larger RSA
   key sizes was testbed before 2048-bits key was used in VeriSgin ZSK
   signing process.

8.  IANA Considerations

   This document requests no action of the IANA.

9.  Acknowledgments

   The editors would like to acknowledge the contributions of the
   various and many subscribers to the Yeti DNS Project mailing lists,
   including the following people who were involved in the
   implementation and operation of the Yeti DNS testbed itself:

      Tomohiro Ishihara, Antonio Prado, Stephane Bortzmeyer, Mickael
      Jouanne, Pierre Beyssac, Joao Damas, Pavel Khramtsov, Ma Yan,
      Otmar Lendl, Praveen Misra, Carsten Strotmann, Edwin Gomez, Remi
      Gacogne, Guillaume de Lafond, Yves Bovard, Hugo Salgado, Li Zhen,
      Daobiao Gong, Runxia Wan.

   The editors also acknowledge the assistance of the Independent
   Submissions Editorial Board, and of the following reviewers whose
   opinions helped improve the clarity of this document:

      Subramanian Moonesamy, Joe Abley,Paul Mockapetris

10.  References

10.1.  Normative References

   [RFC1034]  Mockapetris, P., "Domain names - concepts and facilities",
              STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987,

   [RFC1035]  Mockapetris, P., "Domain names - implementation and
              specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,
              November 1987, <>.

   [RFC1995]  Ohta, M., "Incremental Zone Transfer in DNS", RFC 1995,
              DOI 10.17487/RFC1995, August 1996,

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   [RFC1996]  Vixie, P., "A Mechanism for Prompt Notification of Zone
              Changes (DNS NOTIFY)", RFC 1996, DOI 10.17487/RFC1996,
              August 1996, <>.

   [RFC5011]  StJohns, M., "Automated Updates of DNS Security (DNSSEC)
              Trust Anchors", STD 74, RFC 5011, DOI 10.17487/RFC5011,
              September 2007, <>.

   [RFC5890]  Klensin, J., "Internationalized Domain Names for
              Applications (IDNA): Definitions and Document Framework",
              RFC 5890, DOI 10.17487/RFC5890, August 2010,

10.2.  Informative References

              "Hintfile Auto Update", 2015,

              APNIC, "How well does ATR actually work?", April 2018,

              Andrews, M., "TCP Fails To Respect IPV6_USE_MIN_MTU",
              draft-andrews-tcp-and-ipv6-use-minmtu-04 (work in
              progress), October 2015.

              Sivaraman, M., Kerr, S., and D. Song, "DNS message
              fragments", draft-muks-dns-message-fragments-00 (work in
              progress), July 2015.

              Song, L., "ATR: Additional Truncated Response for Large
              DNS Response", draft-song-atr-large-resp-00 (work in
              progress), September 2017.

              Jaeggli, J., Colitti, L., Kumari, W., Vyncke, E., Kaeo,
              M., and T. Taylor, "Why Operators Filter Fragments and
              What It Implies", draft-taylor-v6ops-fragdrop-02 (work in
              progress), December 2013.

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              "DNSSEC Key Management Implementation for the Root Zone",
              May 2010, <

              "Root Zone KSK Rollover Plan", 2016,

              "2017 KSK Rollover External Test Plan", July 2016,

              APNIC, "Dealing with IPv6 fragmentation in the DNS",
              August 2017, <

              Abley, J., "Hierarchical Anycast for Global Service
              Distribution", March 2003,

   [ITI2014]  "Identifier Technology Innovation Report", May 2014,

              "A DNSSEC issue during Yeti KSK rollover", 2016,

   [RFC2826]  Internet Architecture Board, "IAB Technical Comment on the
              Unique DNS Root", RFC 2826, DOI 10.17487/RFC2826, May
              2000, <>.

   [RFC2845]  Vixie, P., Gudmundsson, O., Eastlake 3rd, D., and B.
              Wellington, "Secret Key Transaction Authentication for DNS
              (TSIG)", RFC 2845, DOI 10.17487/RFC2845, May 2000,

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   [RFC6219]  Li, X., Bao, C., Chen, M., Zhang, H., and J. Wu, "The
              China Education and Research Network (CERNET) IVI
              Translation Design and Deployment for the IPv4/IPv6
              Coexistence and Transition", RFC 6219,
              DOI 10.17487/RFC6219, May 2011,

   [RFC6891]  Damas, J., Graff, M., and P. Vixie, "Extension Mechanisms
              for DNS (EDNS(0))", STD 75, RFC 6891,
              DOI 10.17487/RFC6891, April 2013,

   [RFC7720]  Blanchet, M. and L-J. Liman, "DNS Root Name Service
              Protocol and Deployment Requirements", BCP 40, RFC 7720,
              DOI 10.17487/RFC7720, December 2015,

   [RFC7872]  Gont, F., Linkova, J., Chown, T., and W. Liu,
              "Observations on the Dropping of Packets with IPv6
              Extension Headers in the Real World", RFC 7872,
              DOI 10.17487/RFC7872, June 2016,

   [RFC8109]  Koch, P., Larson, M., and P. Hoffman, "Initializing a DNS
              Resolver with Priming Queries", BCP 209, RFC 8109,
              DOI 10.17487/RFC8109, March 2017,

   [RFC8324]  Klensin, J., "DNS Privacy, Authorization, Special Uses,
              Encoding, Characters, Matching, and Root Structure: Time
              for Another Look?", RFC 8324, DOI 10.17487/RFC8324,
              February 2018, <>.

   [RRL]      Vixie, P. and V. Schryver, "Response Rate Limiting (RRL)",
              June 2012, <>.

              "Service Expectations of Root Servers", December 2015,

              "History of the Root Server System", November 2016,

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   [TNO2009]  Gijsen, B., Jamakovic, A., and F. Roijers, "Root Scaling
              Study: Description of the DNS Root Scaling Model",
              September 2009,

              Wessels, D., "Thirteen Years of Old J-Root", 2015,

   [YetiLR]   "Observation on Large response issue during Yeti KSK
              rollover", August 2017, <http://yeti-

10.3.  URIs












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Appendix A.  Yeti-Root Hints File

   The following hints file (complete and accurate at the time of
   writing) causes a DNS resolver to use the Yeti DNS testbed in place
   of the production Root Server System and hence participate in
   experiments running on the testbed.

   Note that some lines have been wrapped in the text that follows in
   order to fit within the production constraints of this document.
   Wrapped lines are indicated with a blackslash character ("\"),
   following common convention.

   .                     3600000  IN   NS       3600000  IN   AAAA   240c:f:1:22::6
   .                     3600000  IN   NS      3600000  IN   AAAA   2001:559:8000::6
   .                     3600000  IN   NS    3600000  IN   AAAA   2001:200:1d9::35
   .                     3600000  IN   NS   3600000  IN   AAAA   \
   .                     3600000  IN   NS     3600000  IN   AAAA   \
   .                     3600000  IN   NS    3600000  IN   AAAA   2a02:2810:0:405::250
   .                     3600000  IN   NS         3600000  IN   AAAA   2001:6d0:6d06::53
   .                     3600000  IN   NS     3600000  IN   AAAA   2a01:4f8:161:6106:1::10
   .                     3600000  IN   NS    3600000  IN   AAAA   2001:e30:1c1e:1::333
   .                     3600000  IN   NS \
                         3600000  IN   AAAA   2001:1608:10:167:32e::53
   .                     3600000  IN   NS      3600000  IN   AAAA   \
   .                     3600000  IN   NS     3600000  IN   AAAA   2001:67c:217c:6::2
   .                     3600000  IN   NS      3600000  IN   AAAA   2a02:ec0:200::1
   .                     3600000  IN   NS     3600000  IN   AAAA   2001:620:0:ff::29
   .                     3600000  IN   NS    3600000  IN   AAAA   2001:1398:1:21::8001
   .                     3600000  IN   NS

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   .                     3600000  IN   NS  3600000  IN   AAAA   2001:da8:268:4200::6
   .                     3600000  IN   NS  3600000  IN   AAAA   2400:a980:30ff::6
   .                     3600000  IN   NS     \
                         3600000  IN   AAAA   2c0f:f530::6
   .                     3600000  IN   NS     \
                         3600000  IN   AAAA   2803:80:1004:63::1
   .                     3600000  IN   NS     \
                         3600000  IN   AAAA   2401:c900:1401:3b:c::6
   .                     3600000  IN   NS     \
   xn--r2bi1c.xn--h2bv6c0a.xn--h2brj9c \
                         3600000  IN   AAAA   2001:e30:1c1e:10::333
   .                     3600000  IN   NS   3600000  IN   AAAA   2001:e30:187d::333
   .                     3600000  IN   NS \
                         3600000  IN   AAAA   2001:19f0:0:1133::53
   .                     3600000  IN   NS      3600000  IN   AAAA   2a02:990:100:b01::53:0

Appendix B.  Yeti-Root Server Priming Response

   Here is the reply of a Yeti root name server to a priming request.
   The authoritative server runs NSD.

   ;; Got answer:
   ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 62391
   ;; flags: qr aa rd; QUERY: 1, ANSWER: 26, AUTHORITY: 0, ADDITIONAL: 7
   ;; WARNING: recursion requested but not available

   ; EDNS: version: 0, flags: do; udp: 1460
   ;.                      IN NS


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   .            86400 IN NS
   .            86400 IN NS
   .            86400 IN NS
   .            86400 IN NS
   .            86400 IN NS
   .            86400 IN NS
   .            86400 IN NS
   .            86400 IN NS
   .            86400 IN NS
   .            86400 IN NS
   .            86400 IN NS
   .            86400 IN NS
   .            86400 IN NS
   .            86400 IN NS
   .            86400 IN NS
   .            86400 IN NS
   .            86400 IN NS
   .            86400 IN NS
   .            86400 IN NS
   .            86400 IN NS
   .            86400 IN NS xn--r2bi1c.xn--h2bv6c0a.xn--h2brj9c.
   .            86400 IN NS
   .            86400 IN NS
   .            86400 IN NS
   .            86400 IN NS
   .            86400 IN RRSIG NS 8 0 86400 (
                            20171121050105 20171114050105 26253 .
                            4esLNtD8vdypucffem6n0T0eV1c+7j/eIA== )

   ;; ADDITIONAL SECTION:        86400 IN AAAA 240c:f:1:22::6      86400 IN AAAA 2a01:4f8:161:6106:1::10     86400 IN AAAA 2001:e30:1c1e:1::333       86400 IN AAAA 2a02:ec0:200::1       86400 IN AAAA 2001:19f0:5401:1c3::53       86400 IN AAAA 2a02:990:100:b01::53:0

   ;; Query time: 163 msec
   ;; SERVER: 2001:4b98:dc2:45:216:3eff:fe4b:8c5b#53
   ;; WHEN: Tue Nov 14 16:45:37 +08 2017
   ;; MSG SIZE  rcvd: 1222

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Appendix C.  Active IPv6 Prefixes in Yeti DNS testbed

   | Prefix               | Originator                      | Location |
   | 240c::/28            | BII                             | CN       |
   | 2001:6d0:6d06::/48   | MSK-IX                          | RU       |
   | 2001:1488::/32       | CZ.NIC                          | CZ       |
   | 2001:620::/32        | SWITCH                          | CH       |
   | 2001:470::/32        | Hurricane Electric, Inc.        | US       |
   | 2001:0DA8:0202::/48  | BUPT6-CERNET2                   | CN       |
   | 2001:19f0:6c00::/38  | Choopa, LLC                     | US       |
   | 2001:da8:205::/48    | BJTU6-CERNET2                   | CN       |
   | 2001:62a::/31        | Vienna University Computer      | AT       |
   |                      | Center                          |          |
   | 2001:67c:217c::/48   | AFNIC                           | FR       |
   | 2a02:2478::/32       | Profitbricks GmbH               | DE       |
   | 2001:1398:1::/48     | NIC Chile                       | CL       |
   | 2001:4490:dc4c::/46  | NIB (National Internet          | IN       |
   |                      | Backbone)                       |          |
   | 2001:4b98::/32       | Gandi                           | FR       |
   | 2a02:aa8:0:2000::/52 | T-Systems-Eltec                 | ES       |
   | 2a03:b240::/32       | Netskin GmbH                    | CH       |
   | 2801:1a0::/42        | Universidad de Ibague           | CO       |
   | 2a00:1cc8::/40       | ICT Valle Umbra s.r.l.          | IT       |
   | 2a02:cdc0::/29       | ORG-CdSB1-RIPE                  | IT       |

Appendix D.  Tools developed for Yeti DNS testbed

   Various tools were developed to support the Yeti DNS testbed, a
   selection of which are described briefly below.

   YmmV ("Yeti Many Mirror Verifier") is designed to make it easy and
   safe for a DNS administrator to capture traffic sent from a resolver
   to the Root Server System and to replay it towards Yeti-Root servers.
   Responses from both systems are recorded and compared, and
   differences are logged.  See <>.

   PcapParser is a module used by YmmV which reassembles fragmented IPv6
   datagrams and TCP segments from a PCAP archive and extracts DNS
   messages contained within them.  See <

   DNS-layer-fragmentation implements DNS proxies that perform
   application-level fragmentation of DNS messages, based on
   [I-D.muks-dns-message-fragments].  The idea with these proxies is to
   explore splitting DNS messages in the protocol itself, so they will

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   not by fragmented by the IP layer.  See <

   DNS_ATR is an implementation of DNS Additional Truncated Response
   (ATR), as described in [] [How_ATR_work].
   DNS_ATR acts as a proxy between resolver and authoritative servers,
   forwarding queries and responses as a silent and transparent
   listener.  Responses that are larger than a nominated threshold (1280
   octets by default) trigger additional truncated responses to be sent
   immediately following the large response.  See

Appendix E.  Controversy

   The Yeti DNS Project, its infrastructure and the various experiments
   that have been carried out using that infrastructure, have been
   described by people involved in the project in many public meetings
   at technical venues since its inception.  The mailing lists using
   which the operation of the infrastructure has been coordinated are
   open to join, and their archives are public.  The project as a whole
   has been the subject of robust public discussion.

   Some commentators have expressed concern that the Yeti DNS Project
   is, in effect, operating an alternate root, challenging the IAB's
   comments published in [RFC2826].  Other such alternate roots are
   considered to have caused end-user confusion and instability in the
   namespace of the DNS by the introduction of new top-level labels or
   the different use of top-level labels present in the Root Server
   System.  The coordinators of the Yeti DNS Project do not consider the
   Yeti DNS Project to be an alternate root in this sense, since by
   design the namespace enabled by the Yeti-Root Zone is identical to
   that of the Root Zone.

   Some commentators have expressed concern that the Yeti DNS Project
   seeks to influence or subvert administrative policy relating to the
   Root Server System, in particular in the use of DNSSEC trust anchors
   not published by the IANA and the use of Yeti-Root Servers in regions
   where governments or other organisations have expressed interest in
   operating a Root Server.  The coordinators of the Yeti-Root project
   observe that their mandate is entirely technical and has no ambition
   to influence policy directly; they do hope, however, that technical
   findings from the Yeti DNS Project might act as a useful resource for
   the wider technical community.

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Appendix F.  About This Document

   This section (and sub-sections) has been included as an aid to
   reviewers of this document, and should be removed prior to

F.1.  Venue

   The authors propose that this document proceed as an Independent
   Submission, since it documents work that, although relevant to the
   IETF, has been carried out externally to any IETF working group.
   However, a suitable venue for discussion of this document is the
   dnsop working group.

   Information about the Yeti DNS project and discussion relating to
   particular experiments described in this document can be found at

   This document is maintained in GitHub at <

F.2.  Revision History

F.2.1.  draft-song-yeti-testbed-experience-00 through -03

   Change history is available in the public GitHub repository where
   this document is maintained: <

F.2.2.  draft-song-yeti-testbed-experience-04

   Substantial editorial review and rearrangement of text by Joe Abley
   at request of BII.

   Added what is intended to be a balanced assessment of the controversy
   that has arisen around the Yeti DNS Project, at the request of the
   Independent Submissions Editorial Board.

   Changed the focus of the document from the description of individual
   experiments on a Root-like testbed to the construction and
   motivations of the testbed itself, since that better describes the
   output of the Yeti DNS Project to date.  In the considered opinion of
   this reviewer, the novel approaches taken in the construction of the
   testbed infrastructure and the technical challenges met in doing so
   are useful to record, and the RFC series is a reasonable place to
   record operational experiences related to core Internet

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   Note that due to draft cut-off deadlines some of the technical
   details described in this revision of the document may not exactly
   match operational reality; however, this revision provides an
   indicative level of detail, focus and flow which it is hoped will be
   helpful to reviewers.

F.2.3.  draft-song-yeti-testbed-experience-05

   Added commentary on IPv6-only operation, IPv6 fragmentation,
   applicability to and use by IPv4-only end-users and use of multiple

F.2.4.  draft-song-yeti-testbed-experience-06

   Conclusion; tools; editorial changes.

F.2.5.  draft-song-yeti-testbed-experience-07

   Add section for requirements Notation and Conventions, editorial
   changes according to reviewers' comments.

F.2.6.  draft-song-yeti-testbed-experience-08

   Editorial changes after ISE review.

Authors' Addresses

   Linjian Song (editor)
   Beijing Internet Institute
   2508 Room, 25th Floor, Tower A, Time Fortune
   Beijing  100028
   P. R. China


   Dong Liu
   Beijing Internet Institute
   2508 Room, 25th Floor, Tower A, Time Fortune
   Beijing  100028
   P. R. China


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   Paul Vixie
   11400 La Honda Road
   Woodside, California  94062


   Akira Kato
   Keio University/WIDE Project
   Graduate School of Media Design, 4-1-1 Hiyoshi, Kohoku
   Yokohama  223-8526


   Shane Kerr
   Antoon Coolenlaan 41
   Uithoorn  1422 GN


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