DNSOP Working Group G. Moura
Internet-Draft SIDN Labs/TU Delft
Intended status: Informational W. Hardaker
Expires: October 10, 2020 J. Heidemann
USC/Information Sciences Institute
M. Davids
SIDN Labs
April 08, 2020
Considerations for Large Authoritative DNS Servers Operators
draft-moura-dnsop-authoritative-recommendations-07
Abstract
This document summarizes recent research work exploring Domain Name
System (DNS) configurations and offers specific, tangible
considerations to operators for configuring authoritative servers.
It is possible that the considerations presented in this document
could be applicable in a wider context, such as for any stateless/
short-duration, anycasted service.
This document is not an IETF consensus document: it is published for
informational purposes.
Status of This Memo
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This Internet-Draft will expire on October 10, 2020.
Copyright Notice
Copyright (c) 2020 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Background . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. C1: Use anycast in every authoritative for better load
distribution . . . . . . . . . . . . . . . . . . . . . . . . 4
4. C2: Routing can matter more than locations . . . . . . . . . 6
5. C3: Collecting anycast catchment maps to improve design . . . 7
6. C4: When under stress, employ two strategies . . . . . . . . 8
7. C5: Consider longer time-to-live values whenever possible . . 10
8. Security considerations . . . . . . . . . . . . . . . . . . . 12
9. Privacy Considerations . . . . . . . . . . . . . . . . . . . 12
10. IANA considerations . . . . . . . . . . . . . . . . . . . . . 12
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 13
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 13
12.1. Normative References . . . . . . . . . . . . . . . . . . 13
12.2. Informative References . . . . . . . . . . . . . . . . . 14
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 16
1. Introduction
This document summarizes recent research work exploring DNS
configurations and offers specific tangible considerations to DNS
authoritative server operators (DNS operators hereafter). The
considerations (C1-C5) presented in this document are backed by
previous research work, which used wide-scale Internet measurements
upon which to draw their conclusions. This document describes the
key engineering options, and points readers to the pertinent papers
for details and other research works related to each consideration
here presented.
These considerations are designed for operators of "large"
authoritative servers. In this context, "large" authoritative
servers refers to those with a significant global user population,
like top-level domain (TLD) operators, run by a single or multiple
operators. These considerations may not be appropriate for smaller
domains, such as those used by an organization with users in one city
or region, where goals such as uniform low latency are less strict.
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It is likely that these considerations might be useful in a wider
context, such as for any stateless/short-duration, anycasted service.
Because the conclusions of the studies don't verify this fact, the
wording in this document discusses DNS authoritative services only.
This document is not an IETF consensus document: it is published for
informational purposes.
2. Background
The DNS as main two types of DNS servers: authoritative servers and
recursive resolvers. Figure 1 shows their relationship. An
authoritative server (ATn in Figure 1) knows the content of a DNS
zone from local knowledge, and thus can answer queries about that
zone without needing to query other servers [RFC2181]. A recursive
resolver (Re1-Re3) is a program that extracts information from name
servers in response to client requests [RFC1034]. A client (stub in
Figure 1) refers to stub resolver [RFC1034] that is typically located
within the client software.
+-----+ +-----+ +-----+ +-----+
| AT1 | | AT2 | | AT3 | | AT4 |
+-----+ +-----+ +-----+ +-----+
^ ^ ^ ^
| | | |
| +-----+ | |
+------| Re1 |----+| |
| +-----+ |
| ^ |
| | |
| +----+ +----+ |
+------|Re2 | |Re3 |------+
+----+ +----+
^ ^
| |
| +------+ |
+-| stub |-+
+------+
Figure 1: Relationship between recursive resolvers (Re) and
authoritative name servers (ATn)
DNS queries/responses contribute to a user's perceived perceived
latency and affect user experience [Sigla2014], and the DNS system
has been subject to repeated Denial of Service (DoS) attacks (for
example, in November 2015 [Moura16b]) in order to degrade user
experience.
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To reduce latency and improve resiliency against DoS attacks, DNS
uses several types of server replication. Replication at the
authoritative server level can be achieved with (i) the deployment of
multiple servers for the same zone [RFC1035] (AT1--AT4 in Figure 1),
(ii) the use of IP anycast [RFC1546][RFC4786][RFC7094] that allows
the same IP address to be announced from multiple locations (each of
them referred to as an anycast instance [RFC8499]) and (iii) by using
load balancers to support multiple servers inside a single
(potentially anycasted) instance. As a consequence, there are many
possible ways an authoritative DNS provider can engineer its
production authoritative server network, with multiple viable choices
and no single optimal design.
In the next sections we cover specific considerations (C1-C5) for
large authoritative DNS server operators.
3. C1: Use anycast in every authoritative for better load distribution
Authoritative DNS servers operators announce their authoritative
servers as NS records[RFC1034]. Different authoritatives for a given
zone should return the same content, typically by staying
synchronized using DNS zone transfers (AXFR[RFC5936] and
IXFR[RFC1995]) to coordinate the authoritative zone data to return to
their clients.
DNS heavily relies upon replication to support high reliability,
capacity and to reduce latency [Moura16b]. DNS has two complementary
mechanisms to replicate the service. First, the protocol itself
supports nameserver replication of DNS service for a DNS zone through
the use of multiple nameservers that each operate on different IP
addresses, listed by a zone's NS records. Second, each of these
network addresses can run from multiple physical locations through
the use of IP anycast[RFC1546][RFC4786][RFC7094], by announcing the
same IP address from each instance and allowing Internet routing
(BGP[RFC4271]) to associate clients with their topologically nearest
anycast instance. Outside the DNS protocol, replication can be
achieved by deploying load balancers at each physical location.
Nameserver replication is recommended for all zones (multiple NS
records), and IP anycast is used by most large zones such as the DNS
Root, most top-level domains[Moura16b] and large commercial
enterprises, governments and other organizations.
Most DNS operators strive to reduce latency for users of their
service. However, because they control only their authoritative
servers, and not the recursive resolvers communicating with those
servers, it is difficult to ensure that recursives will be served by
the closest authoritative server. Server selection is up to the
recursive resolver's software implementation, and different software
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vendors and releases employ different criteria to chose which
authoritative servers with which to communicate.
Knowing how recursives choose authoritative servers is a key step to
better engineer the deployment of authoritative servers.
[Mueller17b] evaluates this with a measurement study in which they
deployed seven unicast authoritative name servers in different global
locations and queried these authoritative servers from more than 9k
RIPE authoritative server operators and their respective recursive
resolvers.
In the wild, [Mueller17b] found that recursives query all available
authoritative servers, regardless of the observed latency. But the
distribution of queries tends to be skewed towards authoritatives
with lower latency: the lower the latency between a recursive
resolver and an authoritative server, the more often the recursive
will send queries to that authoritative. These results were obtained
by aggregating results from all vantage points and not specific to
any vendor/version.
The hypothesis is that this behavior is a consequence of two main
criteria employed by resolvers when choosing authoritatives:
performance (lower latency) and diversity of authoritatives, where a
resolver checks all authoritative servers to determine which is
closer and to provide alternatives if one is unavailable.
For a DNS operator, this policy means that latency of all
authoritatives (NS records) matter, so all must be similarly capable,
since all available authoritatives will be queried by most recursive
resolvers. Since unicast cannot deliver good latency worldwide (a
unicast authoritative server in Europe will always have high latency
to resolvers in California, for example, given its geographical
distance), [Mueller17b] recommends to DNS operators that they deploy
equally strong IP anycast in every authoritative server (i.e., on
each NS record , in terms of number of instances and peering, and,
consequently, to phase out unicast, so they can deliver good latency
values to global clients. However, [Mueller17b] also notes that DNS
operators should also take architectural considerations into account
when planning for deploying anycast [RFC1546].
This consideration was deployed at the ".nl" TLD zone, which
originally had seven authoritative severs (mixed unicast/anycast
setup). In early 2018, .nl moved to a setup with 4 anycast
authoritative name servers. This is not to say that .nl was the
first - other zones, have been running anycast only authoritatives
(e.g., .be since 2013). [Mueller17b] contribution is to show that
unicast cannot deliver good latency worldwide, and that anycast has
to be deployed to deliver good latency worldwide.
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4. C2: Routing can matter more than locations
A common metric when choosing an anycast DNS provider or setting up
an anycast service is the number of anycast instances[RFC4786], i.e.,
the number of global locations from which the same address is
announced with BGP. Intuitively, one could think that more instances
will lead to shorter response times.
However, this is not necessarily true. In fact, [Schmidt17a] found
that routing can matter more than the total number of locations.
They analyzed the relationship between the number of anycast
instances and the performance of a service (latency-wise, round-trip
time (RTT)) and measured the overall performance of four DNS Root
servers. The Root DNS is implemented by 13 separate DNS services,
each running on a different IP address, but sharing a common master
data source: the root DNS zone. These are called the 13 DNS Root
Letter Services just the "Root Letters" for short), since each is
assigned a letter from A to M and identified as $letter.root-
servers.net.
In specific, [Schmidt17a] measured the performance of C, F, K and L
root letters, from more than 7.9k RIPE Atlas probes (RIPE Atlas is a
measurement platform with more than 12000 global devices - Atlas
Probes - that provide vantage points that conduct Internet
measurements, and its regularly used by researchers and operators
[RipeAtlas15a] {{RipeAtlas19a}).
[Schmidt17a] found that C-Root, a smaller anycast deployment
consisting of only 8 instances (they refer to anycast instance as
anycast site), provided a very similar overall performance than that
of the much larger deployments of K and L, with 33 and 144 instances
respectively. The median RTT for C, K and L Root was between
30-32ms.
Given that Atlas has better coverage in Europe than other regions,
the authors specifically analyzed results per region and per country
(Figure 5 in [Schmidt17a]), and show that Atlas bias to Europe does
not change the conclusion that location of anycast instances
dominates latency.
[Schmidt17a] consideration for DNS operators when engineering anycast
services is consider factors other than just the number of instances
(such as local routing connectivity) when designing for performance.
They showed that 12 instances can provide reasonable latency, given
they are globally distributed and have good local interconnectivity.
However, more instances can be useful for other reasons, such as when
handling Denial-of-service (DoS) attacks [Moura16b].
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5. C3: Collecting anycast catchment maps to improve design
An anycast DNS service may have several dozens or even more than one
hundred locations (such as L-Root does). Anycast leverages Internet
routing to distribute the incoming queries to a service's distributed
anycast locations; in theory, BGP (the Internet's de facto routing
protocol) forwards incoming queries to a nearby anycast location (in
terms of BGP distance). However, usually queries are not evenly
distributed across all anycast locations, as found in the case of
L-Root [IcannHedge18].
Adding locations to an anycast service may change the load
distribution across all locations. Given that BGP maps clients to
locations, whenever a new location is announced, this new location
may receive more or less traffic than it was engineered for, leading
to suboptimal usage of the service or even stressing the new location
while leaving others underutilized. This is a scenario that
operators constantly face when expanding an anycast service.
Besides, when setting up a new anycast service location, operators
cannot directly estimate the query distribution among the locations
in advance of enabling the new location.
To estimate the query loads across locations of an expanding service
or a when setting up an entirely new service, operators need detailed
anycast maps and catchment estimates (i.e., operators need to know
which prefixes will be matched to which anycast instance). To do
that, [Vries17b] developed a new technique enabling operators to
carry out active measurements, using an open-source tool called
Verfploeter (available at [VerfSrc]). Verfploeter maps a large
portion of the IPv4 address space, allowing DNS operators to predict
both query distribution and clients catchment before deploying new
anycast instances. At the moment of this writing, Verfploeter still
does not support IPv6.
[Vries17b] shows how this technique was used to predict both the
catchment and query load distribution for the new anycast service of
B-Root. Using two anycast instances in Miami (MIA) and Los Angeles
(LAX) from the operational B-Root server, they sent ICMP echo packets
to IP addresses to each IPv4 /24 on the Internet using a source
address within the anycast prefix. Then, they recorded which
instance the ICMP echo replies arrived at based on the Internet's BGP
routing. This analysis resulted in an Internet wide catchment map.
Weighting was then applied to the incoming traffic prefixes based on
of 1 day of B-Root traffic (2017-04-12, DITL datasets [Ditl17]). The
combination of the created catchment mapping and the load per prefix
created an estimate predicting that 81.6% of the traffic would go to
the LAX location. The actual value was 81.4% of traffic going to
LAX, showing that the estimation was pretty close and the Verfploeter
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technique was a excellent method of predicting traffic loads in
advance of a new anycast instance deployment ([Vries17b] also uses
the term anycast site to refer to anycast location).
Besides that, Verfploeter can also be used to estimate how traffic
shifts among locations when BGP manipulations are executed, such as
AS Path prepending that is frequently used by production networks
during DDoS attacks. A new catchment mapping for each prepending
configuration configuration: no prepending, and prepending with 1, 2
or 3 hops at each instance. Then, [Vries17b] shows that this mapping
can accurately estimate the load distribution for each configuration.
An important operational takeaway from [Vries17b] is that DNS
operators can make informed choices when engineering new anycast
locations or when expending new ones by carrying out active
measurements using Verfploeter in advance of operationally enabling
the fully anycast service. Operators can spot sub-optimal routing
situations early, with a fine granularity, and with significantly
better coverage than using traditional measurement platforms such as
RIPE Atlas.
To date, Verfploeter has been deployed on B-Root[Vries17b], on a
operational testbed (Anycast testbed) [AnyTest], and on a large
unnamed operator.
The consideration is therefore to deploy a small test Verfploeter-
enabled platform in advance at a potential anycast locations may
reveal the realizable benefits of using that location as an anycast
interest, potentially saving significant financial and labor costs of
deploying hardware to a new location that was less effective than as
had been hoped.
6. C4: When under stress, employ two strategies
DDoS attacks are becoming bigger, cheaper, and more frequent
[Moura16b]. The most powerful recorded DDoS attack to DNS servers to
date reached 1.2 Tbps, by using IoT devices [Perlroth16]. Such
attacks call for an answer for the following question: how should a
DNS operator engineer its anycast authoritative DNS server react to
the stress of a DDoS attack? This question is investigated in study
[Moura16b] in which empirical observations are grounded with the
following theoretical evaluation of options.
An authoritative DNS server deployed using anycast will have many
server instances distributed over many networks. Ultimately, the
relationship between the DNS provider's network and a client's ISP
will determine which anycast instance will answer queries for a given
client, given that BGP is the protocol that maps clients to specific
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anycast instances by using routing information [RF:KDar02]. As a
consequence, when an anycast authoritative server is under attack,
the load that each anycast instance receives is likely to be unevenly
distributed (a function of the source of the attacks), thus some
instances may be more overloaded than others which is what was
observed analyzing the Root DNS events of Nov. 2015 [Moura16b].
Given the fact that different instances may have different capacity
(bandwidth, CPU, etc.), making a decision about how to react to
stress becomes even more difficult.
In practice, an anycast instance under stress, overloaded with
incoming traffic, has two options:
o It can withdraw or pre-prepend its route to some or to all of its
neighbors, perform other traffic shifting tricks (such as reducing
the propagation of its announcements using BGP
communities[RFC1997]) which shrinks portions of its catchment),
use FlowSpec [RFC5575] or other upstream communication mechanisms
to deploy upstream filtering. The goals of these techniques is to
perform some combination of shifting of both legitimate and attack
traffic to other anycast instances (with hopefully greater
capacity) or to block the traffic entirely.
o Alternatively, it can be become a degraded absorber, continuing to
operate, but with overloaded ingress routers, dropping some
incoming legitimate requests due to queue overflow. However,
continued operation will also absorb traffic from attackers in its
catchment, protecting the other anycast instances.
[Moura16b] saw both of these behaviors in practice in the Root DNS
events, observed through instance reachability and route-trip time
(RTTs). These options represent different uses of an anycast
deployment. The withdrawal strategy causes anycast to respond as a
waterbed, with stress displacing queries from one instance to others.
The absorption strategy behaves as a conventional mattress,
compressing under load, with some queries getting delayed or dropped.
Although described as strategies and policies, these outcomes are the
result of several factors: the combination of operator and host ISP
routing policies, routing implementations withdrawing under load, the
nature of the attack, and the locations of the instances and the
attackers. Some policies are explicit, such as the choice of local-
only anycast instances, or operators removing an instance for
maintenance or modifying routing to manage load. However, under
stress, the choices of withdrawal and absorption can also be results
that emerge from a mix of explicit choices and implementation
details, such as BGP timeout values.
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[Moura16b] speculates that more careful, explicit, and automated
management of policies may provide stronger defenses to overload.
For DNS operators, that means that besides traditional filtering, two
other options are available (withdraw/prepend/communities or isolate
instances), and the best choice depends on the specifics of the
attack.
Note that this consideration refers to the operation of one anycast
service, i.e., one anycast NS record. However, DNS zones with
multiple authoritative anycast servers may expect load to spill from
one anycast server to another, as resolvers switch from authoritative
to authoritative when attempting to resolve a name [Mueller17b].
7. C5: Consider longer time-to-live values whenever possible
Caching is the cornerstone of good DNS performance and reliability.
A 15 ms response to a new DNS query is fast, but a 1 ms cache hit to
a repeat query is far faster. Caching also protects users from short
outages and can mute even significant DDoS attacks [Moura18b].
DNS record TTLs (time-to-live values) directly control cache duration
[RFC1034][RFC1035] and, therefore, affect latency, resilience, and
the role of DNS in CDN server selection. Some early work modeled
caches as a function of their TTLs [Jung03a], and recent work
examined their interaction with DNS[Moura18b], but no research
provides considerations about what TTL values are good. With this
goal Moura et. al. [Moura19a] carried out a measurement study
investigating TTL choices and its impact on user experience in the
wild, and not focused on specific resolvers (and their caching
architectures), vendors, or setups.
First, they identified several reasons why operators/zone owners may
want to choose longer or shorter TTLs:
o Longer TTL leads to longer caching, which results in faster
responses, given that cache hits are faster than cache misses in
resolvers. [Moura19a] shows that the increase in the TTL for .uy
TLD from 5 minutes (300s) to 1 day (86400s) reduced the latency
from 15k Atlas vantage points significantly: the median RTT went
from 28.7ms to 8ms, while the 75%ile decreased from 183ms to 21ms.
o Longer caching results in lower DNS traffic: authoritative servers
will experience less traffic if TTLs are extended, given that
repeated queries will be answered by resolver caches.
o Longer caching results in lower cost if DNS is metered: some DNS-
As-A-Service providers charges are metered, with a per query cost
(often added to a fixed monthly cost).
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o Longer caching is more robust to DDoS attacks on DNS: DDoS attacks
on a DNS service provider harmed several prominent websites
[Perlroth16]. Recent work has shown that DNS caching can greatly
reduce the effects of DDoS on DNS, provided caches last longer
than the attack [Moura18b].
o Shorter caching supports operational changes: An easy way to
transition from an old server to a new one is to change the DNS
records. Since there is no method to remove cached DNS records,
the TTL duration represents a necessary transition delay to fully
shift to a new server, so low TTLs allow more rapid transition.
However, when deployments are planned in advance (that is, longer
than the TTL), then TTLs can be lowered ''just-before'' a major
operational change, and raised again once accomplished.
o Shorter caching can help with a DNS-based response to DDoS
attacks: Some DDoS-scrubbing services use DNS to redirect traffic
during an attack. Since DDoS attacks arrive unannounced, DNS-
based traffic redirection requires the TTL be keptquite low at all
times to be ready to respond to a potential attack.
o Shorter caching helps DNS-based load balancing: Many large
services use DNS-based load balancing. Each arriving DNS request
provides an opportunity to adjust load, so short TTLs may be
desired to react more quickly to traffic dynamics. (Although many
recursive resolvers have minimum caching times of tens of seconds,
placing a limit on agility.)
As such, choice of TTL depends in part on external factors so no
single recommendation is appropriate for all. Organizations must
weigh these trade-offs to find a good balance. Still, some
guidelines can be used when choosing TTLs:
o For general users, [Moura19a] recommends longer TTLs, of at least
one hour, and ideally 8, 12, or 24 hours. Assuming planned
maintenance can be scheduled at least a day in advance, long TTLs
have little cost.
o For TLD operators: TLD operators that allow public registration of
domains (such as most ccTLDs and .com, .net, .org) host, in their
zone files, NS records (and glues if in-bailiwick) of their
respective domains. [Moura19a] shows that most resolvers will use
TTL values provided by the child delegations, but some will choose
the TTL provided by the parents. As such, similarly to general
users, [Moura19a] recommends longer TTLs for NS records of their
delegations (at least one hour, preferably more).
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o Users of DNS-based load balancing or DDoS-prevention may require
short TTLs: TTLs may be as short as 5 minutes, although 15 minutes
may provide sufficient agility for many operators. Shorter TTLs
here help agility; they are are an exception to the consideration
for longer TTLs.
o Use A/AAAA and NS records: TTLs of A/AAAA records should be
shorter or equal to the TTL for NS records for in-bailiwick
authoritative DNS servers, given that the authors [Moura19a] found
that, for such scenarios, once NS record expires, their associated
A/AAAA will also be updated (glue is sent by the parents). For
out-of-bailiwick servers, A and NS records are usually cached
independently, so different TTLs, if desired, will be effective.
In either case, short A and AAAA records may be desired if DDoS-
mitigation services are an option.
8. Security considerations
As this document discusses applying research results to operational
deployments, there are no further security considerations, other than
the ones mentioned in the normative references. Most of the
considerations affect mostly operational practice, though a few do
have security related impacts, which we'll summarize at high level.
Specifically, C4 discusses a few strategies to employ when a service
is under stress, providing operators with additional guidance when
handling denial of service attacks.
Similarly, C5 identifies both the operational and security benefits
to using longer time-to-live values.
9. Privacy Considerations
This document does not add any practical new privacy issues, aside
from possible benefits in deploying longer TTLs as suggested in C5.
Longer TTLs may help preserve a user's privacy by reducing the number
of requests that get transmitted in both thec lient-to-resolver and
resolver-to-authoritative cases.
DNS privacy is currently under active study, and future research
efforts by multiple organizations may produce more guidance in this
area.
10. IANA considerations
This document has no IANA actions.
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11. Acknowledgements
This document is a summary of the main considerations of six research
works referred in this document. As such, they were only possible
thanks to the hard work of the authors of these research works.
o Ricardo de O. Schmidt
o Wouter B de Vries
o Moritz Mueller
o Lan Wei
o Cristian Hesselman
o Jan Harm Kuipers
o Pieter-Tjerk de Boer
o Aiko Pras
We would like also to thank the various reviewers of different
versions of this draft: Duane Wessels, Joe Abley, Toema Gavrichenkov,
John Levine, Michael StJohns, Kristof Tuyteleers, Stefan Ubbink,
Klaus Darilion and Samir Jafferali, and comments provided at the IETF
DNSOP session (IETF104).
Besides those, we would like thank those who have been individually
thanked in each research work, RIPE NCC and DNS OARC for their tools
and datasets used in this research, as well as the funding agencies
sponsoring the individual research works.
12. References
12.1. 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>.
[RFC1546] Partridge, C., Mendez, T., and W. Milliken, "Host
Anycasting Service", RFC 1546, DOI 10.17487/RFC1546,
November 1993, <https://www.rfc-editor.org/info/rfc1546>.
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[RFC1995] Ohta, M., "Incremental Zone Transfer in DNS", RFC 1995,
DOI 10.17487/RFC1995, August 1996,
<https://www.rfc-editor.org/info/rfc1995>.
[RFC1997] Chandra, R., Traina, P., and T. Li, "BGP Communities
Attribute", RFC 1997, DOI 10.17487/RFC1997, August 1996,
<https://www.rfc-editor.org/info/rfc1997>.
[RFC2181] Elz, R. and R. Bush, "Clarifications to the DNS
Specification", RFC 2181, DOI 10.17487/RFC2181, July 1997,
<https://www.rfc-editor.org/info/rfc2181>.
[RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
Border Gateway Protocol 4 (BGP-4)", RFC 4271,
DOI 10.17487/RFC4271, January 2006,
<https://www.rfc-editor.org/info/rfc4271>.
[RFC4786] Abley, J. and K. Lindqvist, "Operation of Anycast
Services", BCP 126, RFC 4786, DOI 10.17487/RFC4786,
December 2006, <https://www.rfc-editor.org/info/rfc4786>.
[RFC5575] Marques, P., Sheth, N., Raszuk, R., Greene, B., Mauch, J.,
and D. McPherson, "Dissemination of Flow Specification
Rules", RFC 5575, DOI 10.17487/RFC5575, August 2009,
<https://www.rfc-editor.org/info/rfc5575>.
[RFC5936] Lewis, E. and A. Hoenes, Ed., "DNS Zone Transfer Protocol
(AXFR)", RFC 5936, DOI 10.17487/RFC5936, June 2010,
<https://www.rfc-editor.org/info/rfc5936>.
[RFC7094] McPherson, D., Oran, D., Thaler, D., and E. Osterweil,
"Architectural Considerations of IP Anycast", RFC 7094,
DOI 10.17487/RFC7094, January 2014,
<https://www.rfc-editor.org/info/rfc7094>.
[RFC8499] Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS
Terminology", BCP 219, RFC 8499, DOI 10.17487/RFC8499,
January 2019, <https://www.rfc-editor.org/info/rfc8499>.
12.2. Informative References
[AnyTest] Schmidt, R., "Anycast Testbed", December 2018,
<http://www.anycast-testbed.com/>.
[Ditl17] OARC, D., "2017 DITL data", October 2018,
<https://www.dns-oarc.net/oarc/data/ditl/2017>.
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[IcannHedge18]
ICANN, ., "DNS-STATS - Hedgehog 2.4.1", October 2018,
<http://stats.dns.icann.org/hedgehog/>.
[Jung03a] Jung, J., Berger, A., and H. Balakrishnan, "Modeling TTL-
based Internet caches", ACM 2003 IEEE INFOCOM,
DOI 10.1109/INFCOM.2003.1208693, July 2003,
<http://www.ieee-infocom.org/2003/papers/11_01.PDF>.
[Moura16b]
Moura, G., Schmidt, R., Heidemann, J., Mueller, M., Wei,
L., and C. Hesselman, "Anycast vs DDoS Evaluating the
November 2015 Root DNS Events.", ACM 2016 Internet
Measurement Conference, DOI /10.1145/2987443.2987446,
October 2016,
<https://www.isi.edu/~johnh/PAPERS/Moura16b.pdf>.
[Moura18b]
Moura, G., Heidemann, J., Mueller, M., Schmidt, R., and M.
Davids, "When the Dike Breaks: Dissecting DNS Defenses
During DDos", ACM 2018 Internet Measurement Conference,
DOI 10.1145/3278532.3278534, October 2018,
<https://www.isi.edu/~johnh/PAPERS/Moura18b.pdf>.
[Moura19a]
Moura, G., Heidemann, J., Schmidt, R., and W. Hardaker,
"Cache Me If You Can: Effects of DNS Time-to-Live",
ACM 2019 Internet Measurement Conference,
DOI 10.1145/3355369.3355568, October 2019,
<https://www.isi.edu/~johnh/PAPERS/Moura19b.pdf>.
[Mueller17b]
Mueller, M., Moura, G., Schmidt, R., and J. Heidemann,
"Recursives in the Wild- Engineering Authoritative DNS
Servers.", ACM 2017 Internet Measurement Conference,
DOI 10.1145/3131365.3131366, October 2017,
<https://www.isi.edu/%7ejohnh/PAPERS/Mueller17b.pdf>.
[Perlroth16]
Perlroth, N., "Hackers Used New Weapons to Disrupt Major
Websites Across U.S.", October 2016,
<https://www.nytimes.com/2016/10/22/business/
internet-problems-attack.html>.
[RipeAtlas15a]
Staff, R., "RIPE Atlas A Global Internet Measurement
Network", September 2015, <http://ipj.dreamhosters.com/wp-
content/uploads/issues/2015/ipj18-3.pdf>.
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[RipeAtlas19a]
NCC, R., "Ripe Atlas - RIPE Network Coordination Centre",
September 2019, <https://atlas.ripe.net/>.
[Schmidt17a]
Schmidt, R., Heidemann, J., and J. Kuipers, "Anycast
Latency - How Many Sites Are Enough. In Proceedings of the
Passive and Active Measurement Workshop", PAM Passive and
Active Measurement Conference, March 2017,
<https://www.isi.edu/%7ejohnh/PAPERS/Schmidt17a.pdf>.
[Sigla2014]
Singla, A., Chandrasekaran, B., Godfrey, P., and B. Maggs,
"The Internet at the speed of light. In Proceedings of the
13th ACM Workshop on Hot Topics in Networks (Oct 2014)",
ACM Workshop on Hot Topics in Networks, October 2014,
<http://speedierweb.web.engr.illinois.edu/cspeed/papers/
hotnets14.pdf>.
[VerfSrc] Vries, W., "Verfploeter source code", November 2018,
<https://github.com/Woutifier/verfploeter>.
[Vries17b]
Vries, W., Schmidt, R., Hardaker, W., Heidemann, J., Boer,
P., and A. Pras, "Verfploeter - Broad and Load-Aware
Anycast Mapping", ACM 2017 Internet Measurement
Conference, DOI 10.1145/3131365.3131371, October 2017,
<https://www.isi.edu/%7ejohnh/PAPERS/Vries17b.pdf>.
Authors' Addresses
Giovane C. M. Moura
SIDN Labs/TU Delft
Meander 501
Arnhem 6825 MD
The Netherlands
Phone: +31 26 352 5500
Email: giovane.moura@sidn.nl
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Wes Hardaker
USC/Information Sciences Institute
PO Box 382
Davis 95617-0382
U.S.A.
Phone: +1 (530) 404-0099
Email: ietf@hardakers.net
John Heidemann
USC/Information Sciences Institute
4676 Admiralty Way
Marina Del Rey 90292-6695
U.S.A.
Phone: +1 (310) 448-8708
Email: johnh@isi.edu
Marco Davids
SIDN Labs
Meander 501
Arnhem 6825 MD
The Netherlands
Phone: +31 26 352 5500
Email: marco.davids@sidn.nl
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