Independent Submission
Request for Comments: 8483
Category: Informational
ISSN: 2070-1721
L. Song, Ed.
D. Liu
Beijing Internet Institute
P. Vixie
A. Kato
S. Kerr
October 2018

Yeti DNS Testbed


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. This document aims solely to document the technical and operational experience of deploying a system that is similar to but different from the Root Server system (on which the Internet's Domain Name System is designed and built).

Status of This Memo

This document is not an Internet Standards Track specification; it is published for informational purposes.

This is a contribution to the RFC Series, independently of any other RFC stream. The RFC Editor has chosen to publish this document at its discretion and makes no statement about its value for implementation or deployment. Documents approved for publication by the RFC Editor are not candidates for any level of Internet Standard; see Section 2 of RFC 7841.

Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at

Copyright Notice

Copyright © 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.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Requirements Notation and Conventions . . . . . . . . . . . .   5
   3.  Areas of Study  . . . . . . . . . . . . . . . . . . . . . . .   5
     3.1.  Implementation of a Testbed like the Root Server System .   5
     3.2.  Yeti-Root Zone Distribution . . . . . . . . . . . . . . .   5
     3.3.  Yeti-Root Server Names and Addressing . . . . . . . . . .   5
     3.4.  IPv6-Only Yeti-Root Servers . . . . . . . . . . . . . . .   6
     3.5.  DNSSEC in the Yeti-Root Zone  . . . . . . . . . . . . . .   6
   4.  Yeti DNS Testbed Infrastructure . . . . . . . . . . . . . . .   7
     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  . . . . . . . . . . . . . . . . .  18
       5.1.2.  Serving IPv4-Only End-Users . . . . . . . . . . . . .  19
     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 . . . . . . . . .  21
     5.3.  DNSSEC KSK Rollover . . . . . . . . . . . . . . . . . . .  22
       5.3.1.  Failure-Case KSK Rollover . . . . . . . . . . . . . .  22
       5.3.2.  KSK Rollover vs. BIND9 Views  . . . . . . . . . . . .  22
       5.3.3.  Large Responses during KSK Rollover . . . . . . . . .  23
     5.4.  Capture of Large DNS Response . . . . . . . . . . . . . .  24
     5.5.  Automated Maintenance of the Hints File . . . . . . . . .  24
     5.6.  Root Label Compression in Knot DNS Server . . . . . . . .  25
   6.  Conclusions . . . . . . . . . . . . . . . . . . . . . . . . .  26
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  28
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  28
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  29
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  29
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  29
   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
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .  38
   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 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 (see <>).

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 with the aim of providing a non-production testbed that would be open for use by anyone from the technical community to propose or run experiments designed to answer these kinds of questions. Coordination for the project was provided by BII, TISF, and the WIDE Project. Thus, Yeti DNS is an independently coordinated project and is not affiliated with the IETF, ICANN, IANA, or any Root Server Operator. The objectives of the Yeti Project were set by the participants in the project based on experiments that they considered would provide valuable information.

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.

This document describes the motivation for the Yeti project, describes the Yeti testbed infrastructure, and provides the technical and operational experiences of some users of the Yeti testbed. 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.

2. Requirements Notation and Conventions

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

3. Areas of Study

This section provides some examples of the topics that the developers of the Yeti DNS testbed considered important to address. As noted in Section 1, the Yeti DNS is an independently coordinated project and is not affiliated with the IETF, ICANN, IANA, or any Root Server Operator. Thus, the topics and areas for study were selected by (and for) the proponents of the Yeti project to address their own concerns and in the hope that the information and tools provided would be of wider interest.

Each example included below is illustrated with indicative questions.

3.1. Implementation of a Testbed like the Root Server System

  • 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?
  • 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

  • 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 increases?

3.3. Yeti-Root Server Names and Addressing

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

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

  • Is it practical to sign the Yeti-Root zone using multiple, independently operated DNSSEC signers and multiple corresponding Zone Signing Keys (ZSKs)?
   o  To what extent is [RFC5011] ("Automated Updates of DNS Security
      (DNSSEC) Trust Anchors") supported by resolvers?
  • Does the KSK Rollover plan designed and in the process of being implemented by ICANN work as expected on the Yeti testbed?
  • What is the operational impact of using much larger RSA key sizes in the ZSKs used in a root?
  • 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 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 as bogus by any validator using the production Root Server system's root zone trust anchor set.

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 is described in more detail in the sections that follow.

                         ,-- / 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 the 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 (DMs). DMs update their zone on a schedule described in Section 4.1. Each DM that updates the latest zone can notify all roots, so the zone transfer can happen 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.

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 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, K-Root, and L-Root; two servers XFR.CJR.DNS.ICANN.ORG and XFR.LAX.DNS.ICANN.ORG; and 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 intends to provide a basic structure to implement the idea of shared zone control as proposed in [ITI2014].

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, the 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. The approaches are discussed in Sections 4.2.1 and 4.2.2.

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.

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".
  1. All DNSKEY, RRSIG, and NSEC records are removed.
  1. The apex Name Server (NS) RRset is removed, with the corresponding root server glue (A and AAAA) RRsets.
  1. A Yeti DNSKEY RRset is added to the apex, comprising the public parts of all Yeti KSK and ZSKs.
  1. A Yeti NS RRset is added to the apex that includes all Yeti-Root servers.
   7.  Glue records (AAAA only, since Yeti-Root servers are v6-only) for
       all Yeti-Root servers are added.
  1. 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 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; instead, it takes place on a central Hidden Master. The production of signed DNSKEY RRsets is analogous to the use of Signed Key Responses (SKRs) produced during ICANN KSK key ceremonies [ICANN2010].

Each DM now retrieves source data (with a premodified 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 [PINZ], 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 would 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.

This approach has been suggested in order to keep minimal changes from the 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, thereby 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. This 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 (TSIGs) [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 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 cooperative 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 a chance to check and edit the changes. When the serial number of the root zone passes the number chosen, the changes are 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 DMs' repositories as follows:

             $ git remote -v
             origin (fetch)
             origin (push)
             origin (push)
             origin (push)
   For more detailed information on DM synchronization, please see this
   document in Yeti's GitHub repository: <

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, where 512 bytes is 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 to minimize the priming response in a modern DNS ecosystem where EDNS(0) is prevalent.

Priming responses from Yeti-Root servers (unlike those from Root Servers) do not always include server addresses in the additional section. 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, on the EDNS buffer size in use).

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

  • Require use of DNS implementations that exhibit a desired behavior in the priming response.
  • Modify nameserver software or configuration as used by Yeti-Root servers.
  • 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 because 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 a label as specified in IDNA2008 [RFC5890] (it is shown in the following list in punycode).

   | 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 servers 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, because of the IPv6-only Internet of the foreseeable future, and hence the Yeti-Root hints file contains no IPv4 addresses and the Yeti-Root zone contains no IPv4 glue records. Note that the rationale of an IPv6-only testbed is to test whether an IPv6-only root can survive any problem or impact when IPv4 is turned off, much like the context of the IETF SUNSET4 WG [SUNSET4].

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, 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 writing:

  • Platform: 18 of 25 Yeti-Root servers are implemented on a Virtual Private Server (VPS) rather than bare metal.
  • 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 on Windows Server 2016.
  • DNS software: 16 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); 1 uses PowerDNS (4.1.3); and 1 uses MS DNS (10.0.14300.1000).

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 an efficient cache mechanism, the mean query rate is less than 100 qps in the Yeti testbed, but a variety of sources were observed as active during 2017, as summarized in Appendix 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) that was subsequently modified and replayed towards Yeti-Root servers.

4.8. Traffic Capture and Analysis

Traffic capture of queries and responses 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

   o  dnscap <> or
  • pcapdump, part of the pcaputils Debian package <>, with a patch to facilitate triggered file upload (see < cgi-bin/bugreport.cgi?bug=545985>).

PCAP-format files containing packet captures are uploaded using rsync to central storage.

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 the Yeti DNS mailing list archives < discuss/> and on the Yeti DNS blog <>.

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 optimization 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 impact.

Many of the experimental design choices described in this document were expected to trigger larger responses. For example, the choice 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 records and their corresponding glue records); 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 ZSKs and 2 KSKs). Therefore, an increased incidence of fragmentation was expected.

The Yeti DNS testbed provides service on IPv6 only. However, middleboxes (such as firewalls and some routers) are not friendly on IPv6 fragments. There are reports of a notable packet drop rate due to the mistreatment of middleboxes on IPv6 fragments [FRAGDROP] [RFC7872]. One APNIC study [IPv6-frag-DNS] reported that 37% of endpoints using IPv6-capable DNS resolvers 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 set up 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 when using TCP to transfer the Yeti- Root zone from a DM. 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 Maximum Segment Size (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 [USE_MIN_MTU]. The mismatch appears to cause outbound segments of a size greater 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 organizations, including resolution of names to IPv4 addresses and resolution by IPv4-only end-user devices.

Some participants, recognizing 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. In one case (CERNET2), this was done by assigning IPv4 addresses to Yeti-Root servers and mapping them in dual-stack IVI translation devices [RFC6219].

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 that 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 synchronization.

Each DM in the Yeti testbed served a Yeti-Root zone that was 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 Sections 4.2.1 and 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.

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- consistent.

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.

Given this distribution mechanism, it might be expected 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. Upon investigation, this was found to be 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 were 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 for doing the transformation of Root Zone to Yeti-Root zone (Section 4.2.2) introduces a situation where mixed RRSIGs from different DM ZSKs are cached in one resolver.

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 was observed in the resolver's DNSSEC log that the process of verifying an RDATA set shows "success" with a key (keyid) in the DNSKEY RRset. It was implemented later in three DMs that were 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 being monitored and had set a reporting trigger if anything was wrong. In addition, the Yeti mailing list is open for error reports from other participants. So far, the Yeti testbed has been operated in this configuration (with multiple ZSKs) for 2 years. This configuration has proven workable and reliable, even when rollovers of individual ZSKs are 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 produces a larger response to the query for the DNSKEY RRset especially during the KSK rollover.

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.

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, 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:

              |                 | Old Key: 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 that was 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 that was subsequently highlighted by the Internet Systems Consortium (ISC) in their general advice relating to KSK rollover in the root zone to users of BIND 9 [ISC-BIND]. 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.

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 outgoing 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 observed:

  • 3 ZSKs and 2 KSKs, DNSKEY response of 1975 octets;
  • 3 ZSKs and 1 KSK, DNSKEY response of 1414 octets; and
  • 2 ZSKs 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.

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 the "Yeti Many Mirror Verifier" (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 to perform 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 Maintenance of the Hints File

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 files is minimal, likely due to the very low frequency of such renumbering events. Even the oldest of hints files 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 follows.

  1. Use the local resolver to obtain a response to the query "./IN/NS".
  1. Use the local resolver to obtain a set of IPv4 and IPv6 addresses for each name server.
  1. Validate all signatures obtained from the local resolvers and confirm that all data is signed.
  1. 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, and can be represented as one of

  1. a sequence of labels ending in a zero octet;
  1. a pointer; or
  1. 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 releases.

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 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:

  • 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).
  • 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).
  • ZSK size increased to 2048 bits and multiple KSK rollovers executed to exercise support of RFC 5011 in validating resolvers; identification of pitfalls relating to views in BIND9 when configured with "managed-keys" (see Section 5.3).
  • 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).
  • It was observed that Knot 2.0 performed label compression on the root (empty) label. This resulted 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).
  • 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 complaints have reached Yeti's mailing list during Yeti normal operation. Adding more instances into the Yeti root system may help to 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:

  • 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.
  • 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 challenge.
  • 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. This would be so 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.
  • 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.
  • DNS is a tree-based hierarchical database. Mathematically, it has a root node and dependency between parent and child nodes. So, any failures and instability of parent nodes (Root in Yeti's case) may impact their child nodes if there is a human mistake, a malicious attack, or even an earthquake. It is proposed to define technology and practices to allow any organization, from the smallest company to nations, to be self-sufficient in their DNS.
  • In Section 3.12 of [RFC8324], a "Centrally Controlled Root" is viewed as an issue of DNS. In future work, it would be interesting to test some technical tools like blockchain [BC] to either remove the technical requirement for a central authority over the root or enhance the security and stability of the existing Root.

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, a hacker may compromise one DM's Git repository and push unwanted changes to the Yeti DM system; this may introduce a bad root server or bad key for a period of time.

The Yeti resolver needs the bootstrapping files to join the testbed, like the hints file and trust anchor of Yeti. All required information is published on <> and <>. If a hacker tampers with those websites by creating a fake page, a new resolver may lose its way and be configured with a bad root.

DNSSEC is an important research goal in the 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 RFC 5011, and we do have some observations (see Section 5.3). In addition, larger RSA key sizes were used in the testbed before 2048-bit keys were used in the ZSK signing process of the IANA Root zone.

8. IANA Considerations

This document has no IANA actions.

9. References

9.1. 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,
   [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,

9.2. Informative References

   [ATR]      Song, L., "ATR: Additional Truncation Response for Large
              DNS Response", Work in Progress, draft-song-atr-large-
              resp-02, August 2018.
   [BC]       Wikipedia, "Blockchain", September 2018,
   [FRAGDROP] Jaeggli, J., Colitti, L., Kumari, W., Vyncke, E., Kaeo,
              M., and T. Taylor, "Why Operators Filter Fragments and
              What It Implies", Work in Progress, draft-taylor-v6ops-
              fragdrop-02, December 2013.


              Sivaraman, M., Kerr, S., and D. Song, "DNS message
              fragments", Work in Progress, draft-muks-dns-message-
              fragments-00, July 2015.


              "Hintfile Auto Update", commit de428c0, October 2015,


              Huston, G., "How well does ATR actually work?",
              APNIC blog, April 2018,


              Schlyter, J., Lamb, R., and R. Balasubramanian, "DNSSEC
              Key Management Implementation for the Root Zone (DRAFT)",
              May 2010, <


              Design Team, "Root Zone KSK Rollover Plan", March 2016,


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




              Huston, G., "Dealing with IPv6 fragmentation in the DNS",
              APNIC blog, August 2017,
   [ISC-BIND] Risk, V., "2017 Root Key Rollover - What Does it Mean for
              BIND Users?", Internet Systems Consortium, December 2016,


              Abley, J., "Hierarchical Anycast for Global Service
              Distribution", March 2003,
   [ITI2014]  ICANN, "Identifier Technology Innovation Report", May
              2014, <


              Song, D., "A DNSSEC issue during Yeti KSK rollover", Yeti
              DNS blog, October 2016, <
   [PINZ]     Song, D., "Yeti experiment plan for PINZ", Yeti DNS blog,
              May 2018, <
   [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,
   [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 in the
              Domain Name System (DNS RRL)", June 2012,
   [RSSAC001] Root Server System Advisory Committee (RSSAC), "Service
              Expectations of Root Servers", RSSAC001 Version 1,
              December 2015,
   [RSSAC023] Root Server System Advisory Committee (RSSAC), "History of
              the Root Server System", November 2016,
   [SUNSET4]  IETF, "Sunsetting IPv4 (sunset4) Concluded WG",
   [TNO2009]  Gijsen, B., Jamakovic, A., and F. Roijers, "Root Scaling
              Study: Description of the DNS Root Scaling Model",
              TNO report, September 2009,


              Andrews, M., "TCP Fails To Respect IPV6_USE_MIN_MTU", Work
              in Progress, draft-andrews-tcp-and-ipv6-use-minmtu-04,
              October 2015.


              Wessels, D., Castonguay, J., and P. Barber, "Thirteen
              Years of 'Old J-Root'", DNS-OARC Fall 2015 Workshop,
              October 2015, <
   [YetiLR]   "Observation on Large response issue during Yeti KSK
              rollover", Yeti DNS blog, August 2017,

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  3600000  IN   AAAA   2001:da8:a3:a027::6
   .                     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
   .            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

Appendix C. Active IPv6 Prefixes in Yeti DNS Testbed

The following table shows the prefixes that were active during 2017.

   | 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 < PcapParser>.

DNS-layer-fragmentation implements DNS proxies that perform application-level fragmentation of DNS messages, based on [FRAGMENTS]. The idea with these proxies is to explore splitting DNS messages in the protocol itself, so they will not by fragmented by the IP layer. See < Fragmentation>.

DNS_ATR is an implementation of DNS Additional Truncated Response (ATR), as described in [ATR] and [HOW_ATR_WORKS]. 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 < DNS_ATR>.

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 organizations 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.


Firstly, the authors would like to acknowledge the contributions from the people who were involved in the implementation and operation of the Yeti DNS by donating their time and resources. They are:

Tomohiro Ishihara, Antonio Prado, Stephane Bortzmeyer, Mickael Jouanne, Pierre Beyssac, Joao Damas, Pavel Khramtsov, Dmitry Burkov, Dima Burkov, Kovalenko Dmitry, Otmar Lendl, Praveen Misra, Carsten Strotmann, Edwin Gomez, Daniel Stirnimann, Andreas Schulze, Remi Gacogne, Guillaume de Lafond, Yves Bovard, Hugo Salgado, Kees Monshouwer, Li Zhen, Daobiao Gong, Andreas Schulze, James Cloos, and Runxia Wan.

Thanks to all people who gave important advice and comments to Yeti, either in face-to-face meetings or virtually via phone or mailing list. Some of the individuals are as follows:

Wu Hequan, Zhou Hongren, Cheng Yunqing, Xia Chongfeng, Tang Xiongyan, Li Yuxiao, Feng Ming, Zhang Tongxu, Duan Xiaodong, Wang Yang, Wang JiYe, Wang Lei, Zhao Zhifeng, Chen Wei, Wang Wei, Wang Jilong, Du Yuejing, Tan XiaoSheng, Chen Shangyi, Huang Chenqing, Ma Yan, Li Xing, Cui Yong, Bi Jun, Duan Haixing, Marc Blanchet, Andrew Sullivan, Suzanne Wolf, Terry Manderson, Geoff Huston, Jaap Akkerhuis, Kaveh Ranjbar, Jun Murai, Paul Wilson, and Kilnam Chonm.

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

Joe Abley, Paul Mockapetris, and Subramanian Moonesamy.

Authors' Addresses

   Linjian Song (editor)
   Beijing Internet Institute
   2nd Floor, Building 5, No.58 Jing Hai Wu Lu, BDA
   Beijing  100176
   Dong Liu
   Beijing Internet Institute
   2nd Floor, Building 5, No.58 Jing Hai Wu Lu, BDA
   Beijing  100176
   Paul Vixie
   11400 La Honda Road
   Woodside, California  94062
   United States of America
   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
   The Netherlands