wdiff rfc9520.alt-original rfc9520.txt

Internet Engineering Task Force (IETF) D. Wessels
Internet-Draft
Request for Comments: 9520 W. Carroll
Updates: 2308, 4035, 4697 (if approved) M. Thomas
Intended status:
Category: Standards Track Verisign
Expires: 24 March 2024 21 September
ISSN: 2070-1721 December 2023

Negative Caching of DNS Resolution Failures
draft-ietf-dnsop-caching-resolution-failures-08

Abstract

In the DNS, resolvers employ caching to reduce both latency for end
users and load on authoritative name servers. The process of
resolution may result in one of three types of responses: (1) a
response containing the requested data; data, (2) a response indicating the
requested data does not exist; exist, or (3) a non-response due to a
resolution failure in which the resolver does not receive any useful
information regarding the data's existence. This document concerns
itself only with the third type.

RFC 2308 specifies requirements for DNS negative caching. There,
caching of type (2) TYPE 2 responses is mandatory and caching of type (3) TYPE 3
responses is optional. This document updates RFC 2308 to require
negative caching for DNS resolution failures.

RFC 4035 allows DNSSEC validation failure caching. This document
updates RFC 4035 to require caching for DNSSEC validation failures.

RFC 4697 prohibits aggressive requerying for NS records at a failed
zone's parent zone. This document updates RFC 4697 to expand this
requirement to all query types and to all ancestor zones.

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 an Internet Standards Track document.

This document is a product of the Internet Engineering Task Force
(IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list It represents the consensus of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.

Internet-Drafts are draft documents valid the IETF community. It has
received public review and has been approved for a maximum publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 7841.

Information about the current status of six months this document, any errata,
and how to provide feedback on it may be updated, replaced, or obsoleted by other documents obtained 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 24 March 2024.
https://www.rfc-editor.org/info/rfc9520.

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Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Motivation . . . . . . . . . . . . . . . . . . . . . . . 3
1.2. Related Work . . . . . . . . . . . . . . . . . . . . . . 5
1.3. Terminology . . . . . . . . . . . . . . . . . . . . . . . 6
2. Conditions That Lead to DNS Resolution Failures . . . . . . . 6
2.1. SERVFAIL Responses . . . . . . . . . . . . . . . . . . . 7
2.2. REFUSED Responses . . . . . . . . . . . . . . . . . . . . 7
2.3. Timeouts and Unreachable Servers . . . . . . . . . . . . 8
2.4. Delegation Loops . . . . . . . . . . . . . . . . . . . . 8
2.5. Alias Loops . . . . . . . . . . . . . . . . . . . . . . . 9
2.6. DNSSEC Validation Failures . . . . . . . . . . . . . . . 9
2.7. FORMERR Responses . . . . . . . . . . . . . . . . . . . . 9
3. Requirements for Caching DNS Resolution Failures . . . . . . 10
3.1. Retries and Timeouts . . . . . . . . . . . . . . . . . . 10
3.2. Caching . . . . . . . . . . . . . . . . . . . . . . . . . 10
3.3. Requerying Delegation Information . . . . . . . . . . . . 11
3.4. DNSSEC Validation Failures . . . . . . . . . . . . . . . 11
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
5. Security Considerations . . . . . . . . . . . . . . . . . . . 12
6. Privacy Considerations . . . . . . . . . . . . . . . . . . . 12
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 16
7.1. Normative References . . . . . . . . . . . . . . . . . . 16
7.2. Informative References . . . . . . . . . . . . . . . . . 17
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 19
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 19

1. Introduction

Caching has always been a fundamental component of DNS resolution on
the Internet. For example example, [RFC0882] states:

"The

| The sheer size of the database and frequency of updates suggest
| that it must be maintained in a distributed manner, with local
| caching to improve performance." performance.

The early DNS RFCs ([RFC0882], [RFC0883], [RFC1034], and [RFC1035])
primarily discuss caching in the context of what [RFC2308] calls
"positive" responses,
"positive responses", that is, when the response includes the
requested data. In this case, a TTL is associated with each resource
record Resource
Record (RR) in the response. Resolvers can cache and reuse the data
until the TTL expires.

Section 4.3.4 of [RFC1034] describes negative response caching, but
notes it is optional and only talks about name errors (NXDOMAIN).
This is the origin of using the SOA MINIMUM field as a negative
caching TTL.

[RFC2308] updated [RFC1034] to specify new requirements for DNS
negative caching, including making it mandatory for caching resolvers
to cache name error (NXDOMAIN) and no data (NODATA) responses when a an
SOA record is available to provide a TTL. [RFC2308] further
specified optional negative caching for two DNS resolution failure
cases: server failure and dead / unreachable dead/unreachable servers.

This document updates [RFC2308] to require negative caching of all
DNS resolution failures and provides additional examples of
resolution failures. This document also updates failures, [RFC4035] to require caching for DNSSEC
validation failures failures, as well as [RFC4697] to expand the scope of
prohibiting aggressive requerying for NS records at a failed zone's
parent zone to all query types and to all ancestor zones.

1.1. Motivation

Operators of DNS services have known for some time that recursive
resolvers become more aggressive when they experience resolution
failures. A number of different anecdotes, experiments, and
incidents support this claim.

In December 2009, a secondary server for a number of in-addr.arpa
subdomains saw its traffic suddenly double, and queries of type
DNSKEY in particular increase by approximately two orders of
magnitude, coinciding with a DNSSEC key rollover by the zone operator
[roll-over-and-die].
[DNSSEC-ROLLOVER]. This predated a signed root zone zone, and an
operating system vendor was providing non-root trust anchors to the
recursive resolver, which became out of date following the rollover.
Unable to validate responses for the affected in-addr.arpa zones,
recursive resolvers aggressively retried their queries.

In 2016, the internet Internet infrastructure company Dyn experienced a large
attack that impacted many high-profile customers. As documented in a
technical presentation detailing the attack [dyn-attack], (see [RETRY-STORM]), Dyn
staff wrote: "At

| At this point we are now experiencing botnet attack traffic and
| what is best classified as a 'retry storm'. "retry storm"
|
| Looking at certain large recursive platforms > 10x normal volume." volume

In 2018 2018, the root zone key signing key Key Signing Key (KSK) was rolled over
[root-ksk-roll].
[KSK-ROLLOVER]. Throughout the rollover period, the root servers
experienced a significant increase in DNSKEY queries. Before the
rollover, a.root-servers.net and j.root-servers.net together received
about 15 million DNSKEY queries per day. At the end of the
revocation period, they received 1.2 billion per day -- day: an 80x
increase. Removal of the revoked key from the zone caused DNSKEY
queries to drop to post-rollover but pre-revoke levels, indicating
there is still a population of recursive resolvers using the previous
root trust anchor and aggressively retrying DNSKEY queries.

In 2021, Verisign researchers used botnet query traffic to
demonstrate that certain large, large public recursive DNS services exhibit
very high query rates when all authoritative name servers for a zone
return REFUSED refused (REFUSED) or SERVFAIL [botnet]. server failure (SERVFAIL) responses (see
[BOTNET]). When the authoritative servers were configured normally,
query rates for a single botnet domain averaged approximately 50
queries per second. However, with the servers configured to return
SERVFAIL, the query rate increased to 60,000 per second.
Furthermore, increases were also observed at the
Root root and TLD Top-Level
Domain (TLD) levels, even though delegations at those levels were
unchanged and continued operating normally.

Later that same year, on October 4, Facebook experienced a widespread
and well-publicized outage [fb-outage]. [FB-OUTAGE]. During the 6-hour outage,
none of Facebook's authoritative name servers were reachable and did
not respond to queries. Recursive name servers attempting to resolve
Facebook domains experienced timeouts. During this time, query
traffic on the .COM/.NET infrastructure increased from 7,000 to
900,000 queries per second [fb-outage-verisign]. [OUTAGE-RESOLVER].

1.2. Related Work

[RFC2308] describes negative caching for four types of DNS queries
and responses: Name name errors, no data, server failures, and dead / dead/
unreachable servers. It places the strongest requirements on
negative caching for name errors and no data responses, while server
failures and dead servers are left as optional.

[RFC4697] is a Best Current Practice that documents observed
resolution misbehaviors. It describes a number of situations that
can lead to excessive queries from recursive resolvers, including: including
requerying for delegation data, lame servers, responses blocked by
firewalls, and records with zero TTL. [RFC4697] makes a number of
recommendations, varying from "SHOULD" to "MUST."

An expired Internet-Draft "MUST".

[THUNDERING-HERD] describes "The DNS thundering herd problem"
[thundering-herd] as a
situation arising when cached data expires at the same time for a
large number of users. Although that document is not focused on
negative caching, it does describe the benefits of combining multiple, multiple
identical queries to upstream name servers. That is, when a
recursive resolver receives multiple queries for the same name,
class, and type that cannot be answered from cached data, it should
combine or join them into a single upstream query, query rather than emit repeated,
repeated identical upstream queries.

[RFC5452], "Measures for Making DNS More Resilient against Forged
Answers,"
Answers", includes a section that describes the phenomenon known as
birthday attacks.
"Birthday Attacks". Here, again, the problem arises when a recursive
resolver emits multiple, multiple identical upstream queries. Multiple
outstanding queries makes make it easier for an attacker to guess and
correctly match some of the DNS message parameters, such as the port
number and ID field. This situation is further exacerbated in the
case of timeout-based resolution failures. DNSSEC, of Of course, DNSSEC is a
suitable defense to spoofing attacks.

[RFC8767] describes "Serving Stale Data to Improve DNS Resiliency." Resiliency".
This permits a recursive resolver to return possibly stale data when
it is unable to refresh cached, expired data. It introduces the idea
of a failure recheck timer and says: "Attempts

| Attempts to refresh from non-
responsive non-responsive or otherwise failing
| authoritative nameservers are recommended to be done no more
| frequently than every 30 seconds." seconds.

1.3. Terminology

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.

DNS Transport: transport: In this document, DNS transport "DNS transport" means a protocol
used to transport DNS messages between a client and a server.
This includes "classic DNS" transports, i.e., DNS-over-UDP and
DNS-over-TCP [RFC1034] [RFC7766], as well as newer encrypted DNS
transports
transports, such as DNS-over-TLS [RFC7858], DNS-over-HTTPS
[RFC8484], DNS-over-QUIC [RFC9250], and similar communication of
DNS messages using other protocols. NOTE: Note: at the time of this
writing writing,
not all DNS transports are standardized for all types of
servers, servers
but may become standardized in the future.

2. Conditions That Lead to DNS Resolution Failures

A DNS resolution failure occurs when none of the servers available to
a resolver client provide any useful response data for a particular
query name, type, and class. A response is considered useful when it
provides either the requested data, a referral to a descendant zone,
or an indication that no data exists at the given name.

It is common for resolvers to have multiple servers from which to
choose for a particular query. For example, in the case of stub-to-
recursive, the stub resolver may be configured with multiple
recursive resolver addresses. In the case of recursive-to-
authoritative, a given zone usually has more than one name server (NS
record), each of which can have multiple IP addresses and multiple
DNS transports.

Nothing in this document prevents a resolver from retrying a query at
a different server, server or the same server over a different DNS transport.
In the case of timeouts, a resolver can retry the same server and DNS
transport a limited number of times.

If any one of the available servers provides a useful response, then
it is not considered a resolution failure. However, if none of the
servers for a given query tuple <name, type, class> provide a useful
response, the result is a resolution failure.

Note that NXDOMAIN and NOERROR/NODATA responses are not conditions
for resolution failure. In these cases, the server is providing a
useful response, either indicating either that a name does not exist, exist or that
no data of the requested type exists at the name. These negative
responses can be cached as described in [RFC2308].

The remainder of this section describes a number of different
conditions that can lead to resolution failure. This section is not
exhaustive. Additional conditions may be expected to cause similar
resolution failures.

2.1. SERVFAIL Responses

Server failure is defined in [RFC1035] as as: "The name server was
unable to process this query due to a problem with the name server."
A server failure is signaled by setting the RCODE field to SERVFAIL.

Authoritative servers return SERVFAIL when they don't have any valid
data for a zone. For example, a secondary server has been configured
to serve a particular zone, zone but is unable to retrieve or refresh the
zone data from the primary server.

Recursive servers return SERVFAIL in response to a number of
different conditions, including many described below.

Although the extended DNS errors method exists "primarily to extend
SERVFAIL to provide additional information," it "does not change the
processing of RCODEs" [RFC8914]. This document operates at the level
of resolution failure and does not concern particular causes.

2.2. REFUSED Responses

A name server returns a message with the RCODE field set to REFUSED
when it refuses to process the query, e.g., for policy or other
reasons [RFC1035].

Authoritative servers generally return REFUSED when processing a
query for which they are not authoritative. For example, a server
that is configured to be authoritative for only the example.net zone, zone
may return REFUSED in response to a query for example.com.

Recursive servers generally return REFUSED for query sources that do
not match configured access control lists. For example, a server
that is configured to allow queries from only 2001:db8:1::/48 may
return REFUSED in response to a query from 2001:db8:5::1.

2.3. Timeouts and Unreachable Servers

A timeout occurs when a resolver fails to receive any response from a
server within a reasonable amount of time. Additionally, a DNS
transport may more quickly indicate lack of reachability in a way
that wouldn't be considered a timeout. For example: timeout: for example, an ICMP port
unreachable message, a TCP "connection refused" error, or a TLS
handshake failure. [RFC2308] refers to these conditions collectively
as "dead / unreachable servers." servers".

Note that resolver implementations may have two types of timeouts: a
smaller timeout which that might trigger a query retry and a larger timeout
after which the server is considered unresponsive. Section 3.1
discusses the requirements for resolvers when retrying queries.

Timeouts can present a particular problem for negative caching,
depending on how the resolver handles multiple, multiple outstanding queries
for the same <query name, type, class> tuple. For example, consider
a very popular website in a zone whose name servers are all
unresponsive. A recursive resolver might receive tens or hundreds of
queries per second for the popular that website. If the recursive server
implementation "joins" joins these outstanding queries together, then it only
sends one recursive-to-authoritative query for the numerous pending
stub-to-recursive queries. If, however, However, if the implementation does not
join outstanding queries together, then it sends one
recursive-to-authoritative recursive-to-
authoritative query for each stub-to-recursive query. If the
incoming query rate is high and the timeout is large, this might
result in hundreds or thousands of recursive-to-authoritative queries
while waiting for an authoritative server to time out.

A recursive resolver that does not join outstanding queries together
is more susceptible to birthday attacks ([RFC5452] Birthday Attacks ([RFC5452], Section 5),
especially when those queries result in timeouts.

2.4. Delegation Loops

A delegation loop, or cycle, can occur when one domain utilizes name
servers in a second domain, and the second domain uses name servers
in the first. For example:

FOO.EXAMPLE. NS NS1.EXAMPLE.COM.
FOO.EXAMPLE. NS NS2.EXAMPLE.COM.

EXAMPLE.COM. NS NS1.FOO.EXAMPLE.
EXAMPLE.COM. NS NS2.FOO.EXAMPLE.

In this example, no names under foo.example or example.com can be
resolved because of the delegation loop. Note that a delegation loop
may involve more than two domains. A resolver that does not detect
delegation loops may generate DDoS-levels of attack traffic to
authoritative name servers, as documented in the TsuNAME
vulnerability [TsuNAME].

2.5. Alias Loops

An alias loop, or cycle, can occur when one CNAME or DNAME RR refers
to a second name, which which, in turn turn, is specified as an alias for the
first. For example:

APP.FOO.EXAMPLE. CNAME APP.EXAMPLE.NET.
APP.EXAMPLE.NET. CNAME APP.FOO.EXAMPLE.

The need to detect CNAME loops has been known since at least
[RFC1034]
[RFC1034], which states in Section 3.6.2:

"Of

| Of course, by the robustness principle, domain software should not
| fail when presented with CNAME chains or loops; CNAME chains
| should be followed and CNAME loops signaled signalled as an error." error.

2.6. DNSSEC Validation Failures

For zones that are signed with DNSSEC, a resolution failure can occur
when a security-aware resolver believes it should be able to
establish a chain-of-trust chain of trust for an RRset but is unable to do so,
possibly after trying multiple authoritative name servers. DNSSEC
validation failures may be due to signature mismatch, missing DNSKEY
RRs, problems with denial-of-existence records, clock skew, or other
reasons.

Section 4.7 of [RFC4035] already discusses the requirements and
reasons for caching validation failures. Section 3.4 of this
document strengthens those requirements.

2.7. FORMERR Responses

A name server returns a message with the RCODE field set to FORMERR
when it is unable to interpret the query [RFC1035]. FORMERR
responses are often associated with problems processing EDNS(0)
Extensions Extension
Mechanisms for DNS (EDNS(0)) [RFC6891]. Authoritative servers may
return FORMERR when they do not implement EDNS(0), or when EDNS(0)
option fields are malformed, but not for unknown EDNS(0) options.

Upon receipt of a FORMERR response, some recursive clients will retry
their queries without EDNS(0), while others will not. Nonetheless,
resolution failures from FORMERR responses are rare.

3. Requirements for Caching DNS Resolution Failures

3.1. Retries and Timeouts

A resolver MUST NOT retry a given query to a server address over a
given DNS transport more than twice (i.e., three queries in total)
before considering the server address unresponsive over that DNS
transport for that query.

A resolver MAY retry a given query over a different DNS transport to
the same server if it has reason to believe the DNS transport is
available for that server and is compatible with the resolver's
security policies.

This document does not place any requirements on how long an
implementation should wait before retrying a query (aka a timeout
value), which may be implementation- implementation or configuration-dependent. configuration dependent. It
is generally expected that typical timeout values range from 3 to 30
seconds.

3.2. Caching

Resolvers MUST implement a cache for resolution failures. The
purpose of this cache is to eliminate repeated upstream queries that
cannot be resolved. When an incoming query matches a cached
resolution failure, the resolver MUST NOT send any corresponding
outgoing queries until after the cache entries expire.

Implementation details for such a cache are not specified in this
document. The implementation might cache different resolution
failure conditions differently. For example, DNSSEC validation
failures might be cached according to the queried name, class, and
type, whereas unresponsive servers might be cached only according to
the server's IP address. Developers should document their
implementation choices so that operators know what behaviors to
expect when resolution failures are cached.

Resolvers MUST cache resolution failures for at least 1 second.
Resolvers MAY cache different types of resolution failures for
different (i.e., longer) amounts of time. Consistent with [RFC2308],
resolution failures MUST NOT be cached for longer than 5 minutes.

The minimum cache duration SHOULD be configurable by the operator. A
longer cache duration for resolution failures will reduce the
processing burden from repeated queries, queries but may also increase the
time to recover from transitory issues.

Resolvers SHOULD employ an exponential or linear backoff algorithm to
increase the cache duration for persistent resolution failures. For
example, the initial time for negatively caching a resolution failure
might be set to 5 seconds, seconds and increased after each retry that results
in another resolution failure, up to a configurable maximum, not to
exceed the 5-minute upper limit.

Notwithstanding the above, resolvers SHOULD implement measures to
mitigate resource exhaustion attacks on the failed resolution cache.
That is, the resolver should limit the amount of memory and/or
processing time devoted to this cache.

3.3. Requerying Delegation Information

Section 2.1 of [RFC4697] identifies circumstances in which "every which:

| ...every name server in a zone's NS RRSet is unreachable (e.g.,
| during a network outage), unavailable (e.g., the name server
| process is not running on the server host), or misconfigured
| (e.g., the name server is not authoritative for the given zone,
| also known as 'lame')." "lame").

It prohibits unnecessary "aggressive requerying" to the parent of a non-
responsive
non-responsive zone by sending NS queries.

The problem of aggressive requerying to parent zones is not limited
to queries of type NS. This document updates the requirement from
section
Section 2.1.1 of [RFC4697] to apply more generally:

| Upon encountering a zone whose name servers are all non-responsive, non-
| responsive, a resolver MUST cache the resolution failure.
| Furthermore, the resolver MUST limit queries to the non-responsive
| zone's parent zone (and to other ancestor zones) just as it would
| limit subsequent queries to the non-
responsive non-responsive zone.

3.4. DNSSEC Validation Failures

Section 4.7 of [RFC4035] states:

| To prevent such unnecessary DNS traffic, security-aware resolvers
| MAY cache data with invalid signatures, with some restrictions.

This document updates [RFC4035] with the following, stronger stronger,
requirement:

| To prevent such unnecessary DNS traffic, security-aware resolvers
| MUST cache DNSSEC validation failures, with some restrictions.

One of the restrictions mentioned in [RFC4035] is to use a small TTL
when caching data that fails DNSSEC validation. This is, in part,
because the provided TTL cannot be trusted. The advice from
Section 3.2 herein can be used as guidance on TTLs for caching DNSSEC
validation failures.

4. IANA Considerations

This document has no IANA actions.

5. Security Considerations

As noted in Section 3.2, an attacker might attempt a resource
exhaustion attack by sending queries for a large number of names and/
or types that result in resolution failure. Resolvers SHOULD
implement measures to protect themselves and bound the amount of
memory devoted to caching resolution failures.

A cache poisoning attack (see section Section 2.2 of [RFC7873]) resulting in
denial of service may be possible because failure messages cannot be
signed. An attacker might generate queries and send forged failure
messages, causing the resolver to cease sending queries to the
authoritative name server (see Section 2.6 of [RFC4732] for a similar
"data corruption attack" and Section 5.2 of [TuDoor] for a "DNSDoS
attack"). However, this would require continued spoofing throughout
the backoff period and required repeated attacks due to the 5
minute 5-minute cache
limit. As in section Section 4.1.12 of [RFC4686], this attack's effects
would be "localized and of limited duration." duration".

6. Privacy Considerations

This specification has no impact on user privacy.

7. References

7.1. Normative References

[RFC1034] Mockapetris, P., "Domain names - concepts and facilities",
STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987,
<https://www.rfc-editor.org/info/rfc1034>.

[RFC1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,
November 1987, <https://www.rfc-editor.org/info/rfc1035>.

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.

[RFC2308] Andrews, M., "Negative Caching of DNS Queries (DNS
NCACHE)", RFC 2308, DOI 10.17487/RFC2308, March 1998,
<https://www.rfc-editor.org/info/rfc2308>.

[RFC4035] Arends, R., Austein, R., Larson, M., Massey, D., and S.
Rose, "Protocol Modifications for the DNS Security
Extensions", RFC 4035, DOI 10.17487/RFC4035, March 2005,
<https://www.rfc-editor.org/info/rfc4035>.

[RFC4697] Larson, M. and P. Barber, "Observed DNS Resolution
Misbehavior", BCP 123, RFC 4697, DOI 10.17487/RFC4697,
October 2006, <https://www.rfc-editor.org/info/rfc4697>.

[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.

7.2. Informative References

[botnet]

[BOTNET] Wessels, D. and M. Thomas, "Botnet Traffic Observed at
Various Levels of the DNS Hierarchy", May 2021,
<https://indico.dns-oarc.net/event/38/contributions/841/>.

[dyn-attack]
Sullivan, A., "Dyn, DDoS,

[DNSSEC-ROLLOVER]
Michaleson, G., Wallström, P., Arends, R., and DNS", March 2017,
<https://ccnso.icann.org/sites/default/files/file/field-
file-attach/2017-04/presentation-oracle-dyn-ddos-dns-
13mar17-en.pdf>.

[fb-outage] G. Huston,
"Roll Over and Die?", February 2010,
<https://www.potaroo.net/ispcol/2010-02/rollover.html>.

[FB-OUTAGE]
Janardhan, S., "More details about the October 4 outage",
October 2021, <https://engineering.fb.com/2021/10/05/
networking-traffic/outage-details/>.

[fb-outage-verisign]

[KSK-ROLLOVER]
Müller, M., Thomas, M., Wessels, D., Hardaker, W., Chung,
T., Toorop, W., and R. van Rijswijk-Deij, "Roll, Roll,
Roll Your Root: A Comprehensive Analysis of the First Ever
DNSSEC Root KSK Rollover", IMC '19: Proceedings of the
Internet Measurement Conference, Pages 1-14,
DOI 10.1145/3355369.3355570, October 2019,
<https://doi.org/10.1145/3355369.3355570>.

[OUTAGE-RESOLVER]
Verisign, "Observations on Resolver Behavior During DNS
Outages", 20 January 2022,
<https://blog.verisign.com/security/facebook-dns-outage/>.

[RETRY-STORM]
Sullivan, A., "Dyn, DDoS, and DNS", March 2017,
<https://ccnso.icann.org/sites/default/files/file/field-
file-attach/2017-04/presentation-oracle-dyn-ddos-dns-
13mar17-en.pdf>.

[RFC0882] Mockapetris, P., "Domain names: Concepts and facilities",
RFC 882, DOI 10.17487/RFC0882, November 1983,
<https://www.rfc-editor.org/info/rfc882>.

[RFC0883] Mockapetris, P., "Domain names: Implementation
specification", RFC 883, DOI 10.17487/RFC0883, November
1983, <https://www.rfc-editor.org/info/rfc883>.

[RFC4686] Fenton, J., "Analysis of Threats Motivating DomainKeys
Identified Mail (DKIM)", RFC 4686, DOI 10.17487/RFC4686,
September 2006, <https://www.rfc-editor.org/info/rfc4686>.

[RFC4732] Handley, M., Ed., Rescorla, E., Ed., and IAB, "Internet
Denial-of-Service Considerations", RFC 4732,
DOI 10.17487/RFC4732, December 2006,
<https://www.rfc-editor.org/info/rfc4732>.

[RFC5452] Hubert, A. and R. van Mook, "Measures for Making DNS More
Resilient against Forged Answers", RFC 5452,
DOI 10.17487/RFC5452, January 2009,
<https://www.rfc-editor.org/info/rfc5452>.

[RFC6891] Damas, J., Graff, M., and P. Vixie, "Extension Mechanisms
for DNS (EDNS(0))", STD 75, RFC 6891,
DOI 10.17487/RFC6891, April 2013,
<https://www.rfc-editor.org/info/rfc6891>.

[RFC7766] Dickinson, J., Dickinson, S., Bellis, R., Mankin, A., and
D. Wessels, "DNS Transport over TCP - Implementation
Requirements", RFC 7766, DOI 10.17487/RFC7766, March 2016,
<https://www.rfc-editor.org/info/rfc7766>.

[RFC7858] Hu, Z., Zhu, L., Heidemann, J., Mankin, A., Wessels, D.,
and P. Hoffman, "Specification for DNS over Transport
Layer Security (TLS)", RFC 7858, DOI 10.17487/RFC7858, May
2016, <https://www.rfc-editor.org/info/rfc7858>.

[RFC7873] Eastlake 3rd, D. and M. Andrews, "Domain Name System (DNS)
Cookies", RFC 7873, DOI 10.17487/RFC7873, May 2016,
<https://www.rfc-editor.org/info/rfc7873>.

[RFC8484] Hoffman, P. and P. McManus, "DNS Queries over HTTPS
(DoH)", RFC 8484, DOI 10.17487/RFC8484, October 2018,
<https://www.rfc-editor.org/info/rfc8484>.

[RFC8767] Lawrence, D., Kumari, W., and P. Sood, "Serving Stale Data
to Improve DNS Resiliency", RFC 8767,
DOI 10.17487/RFC8767, March 2020,
<https://www.rfc-editor.org/info/rfc8767>.

[RFC8914] Kumari, W., Hunt, E., Arends, R., Hardaker, W., and D.
Lawrence, "Extended DNS Errors", RFC 8914,
DOI 10.17487/RFC8914, October 2020,
<https://www.rfc-editor.org/info/rfc8914>.

[RFC9250] Huitema, C., Dickinson, S., and A. Mankin, "DNS over
Dedicated QUIC Connections", RFC 9250,
DOI 10.17487/RFC9250, May 2022,
<https://www.rfc-editor.org/info/rfc9250>.

[roll-over-and-die]
Michaleson, G., Wallström, P., Arends, R., and G. Huston,
"Roll Over and Die?", February 2010,
<https://www.potaroo.net/ispcol/2010-02/rollover.html>.

[root-ksk-roll]
Müller, M., Thomas, M., Wessels, D., Hardaker, W., Chung,
T., Toorop, W., and R.v. Rijswijk-Deij, "Roll, Roll, Roll
Your Root: A Comprehensive Analysis of the First Ever
DNSSEC Root KSK Rollover", October 2019,
<https://dl.acm.org/doi/10.1145/3355369.3355570>.

[thundering-herd]

[THUNDERING-HERD]
Sivaraman, M. and C. Liu, "The DNS thundering herd problem
(expired Internet-Draft)",
problem", Work in Progress, Internet-Draft, draft-muks-
dnsop-dns-thundering-herd-00, 25 June 2020,
<https://datatracker.ietf.org/doc/draft-muks-dnsop-dns-
thundering-herd/>.
<https://datatracker.ietf.org/doc/html/draft-muks-dnsop-
dns-thundering-herd-00>.

[TsuNAME] Moura, G. C. M., Castro, S., Heidemann, J., and W.
Hardaker, "TsuNAME: exploiting misconfiguration and
vulnerability to DDoS DNS", IMC '21: Proceedings of the
21st ACM Internet Measurement Conference, Pages 398-418,
DOI 10.1145/3487552.3487824, November 2021,
<https://dl.acm.org/doi/10.1145/3487552.3487824>.
<https://doi.org/10.1145/3487552.3487824>.

[TuDoor] Li, X., Xu, W., Liu, B., Zhang, M., Li, Z., Zhang, J.,
Chang, D., Zheng, X., Wang, C., Chen, J., Duan, H., and Q.
Li, "TuDoor Attack: Systematically Exploring and
Exploiting Logic Vulnerabilities in DNS Response Pre-
processing with Malformed Packets", IEEE Symposium on
Security and Privacy (SP), DOI 10.1109/SP54263.2024.00046,
2024, <https://doi.ieeecomputersociety.org/10.1109/
SP54263.2024.00046>.

Acknowledgments

The authors wish to thank Mukund Sivaraman, Petr Spacek, Peter van
Dijk, Tim Wicinksi, Joe Abley, Evan Hunt, Barry Leiba, Lucas Pardue,
Paul Wouters, and other members of the DNSOP working group Working Group for their
feedback and contributions.

Authors' Addresses

Duane Wessels
Verisign
12061 Bluemont Way
Reston, VA 20190
United States of America
Phone: +1 703 948-3200
Email: dwessels@verisign.com
URI: https://verisign.com

William Carroll
Verisign
12061 Bluemont Way
Reston, VA 20190
United States of America
Phone: +1 703 948-3200
Email: wicarroll@verisign.com
URI: https://verisign.com

Matthew Thomas
Verisign
12061 Bluemont Way
Reston, VA 20190
United States of America
Phone: +1 703 948-3200
Email: mthomas@verisign.com
URI: https://verisign.com