DNSOP Working Group O. Sury
Internet-Draft Internet Systems Consortium
Updates: 7873 (if approved) W. Toorop
Intended status: Standards Track NLnet Labs
Expires: May 7, 2020 D. Eastlake 3rd
Futurewei Technologies
M. Andrews
Internet Systems Consortium
November 4, 2019
Interoperable Domain Name System (DNS) Server Cookies
draft-ietf-dnsop-server-cookies-01
Abstract
DNS cookies, as specified in RFC 7873, are a lightweight DNS
transaction security mechanism that provides limited protection to
DNS servers and clients against a variety of denial-of-service and
amplification, forgery, or cache poisoning attacks by off-path
attackers.
This document provides precise directions for creating Server Cookies
so that an anycast server set including diverse implementations will
interoperate with standard clients.
This document updates [RFC7873]
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on May 7, 2020.
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Copyright Notice
Copyright (c) 2019 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
(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Contents of this document . . . . . . . . . . . . . . . . 3
1.2. Definitions . . . . . . . . . . . . . . . . . . . . . . . 4
2. Changes to [RFC7873] . . . . . . . . . . . . . . . . . . . . 4
3. Constructing a Client Cookie . . . . . . . . . . . . . . . . 4
4. Constructing a Server Cookie . . . . . . . . . . . . . . . . 5
4.1. The Version Sub-Field . . . . . . . . . . . . . . . . . . 6
4.2. The Reserved Sub-Field . . . . . . . . . . . . . . . . . 6
4.3. The Timestamp Sub-Field . . . . . . . . . . . . . . . . . 6
4.4. The Hash Sub-Field . . . . . . . . . . . . . . . . . . . 6
5. Updating the Server Secret . . . . . . . . . . . . . . . . . 7
6. Cookie Algorithms . . . . . . . . . . . . . . . . . . . . . . 8
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
8.1. Normative References . . . . . . . . . . . . . . . . . . 9
8.2. Informative References . . . . . . . . . . . . . . . . . 9
Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 10
Appendix B. Test vectors . . . . . . . . . . . . . . . . . . . . 10
B.1. Learning a new Server Cookie . . . . . . . . . . . . . . 10
B.2. The same client learning a renewed (fresh) Server Cookie 11
B.3. Another client learning a renewed Server Cookie . . . . . 12
B.4. IPv6 query with rolled over secret . . . . . . . . . . . 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 14
1. Introduction
DNS cookies, as specified in [RFC7873], are a lightweight DNS
transaction security mechanism that provides limited protection to
DNS servers and clients against a variety of denial-of-service and
amplification, forgery, or cache poisoning attacks by off-path
attackers. This document specifies a means of producing
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interoperable strong cookies so that an anycast server set including
diverse implementations can be easily configured to interoperate with
standard clients.
The threats considered for DNS Cookies and the properties of the DNS
Security features other than DNS Cookies are discussed in [RFC7873].
In [RFC7873] in Section 6 it is "RECOMMENDED for simplicity that the
same Server Secret be used by each DNS server in a set of anycast
servers." However, how precisely a Server Cookie is calculated from
this Server Secret, is left to the implementation.
This guidance has led to a gallimaufry of DNS Cookie implementations,
calculating the Server Cookie in different ways. As a result, DNS
Cookies are impractical to deploy on multi-vendor anycast networks,
because even when all DNS Software share the same secret, as
RECOMMENDED in Section 6 of [RFC7873], the Server Cookie constructed
by one implementation cannot generally be validated by another.
There is no need for DNS client (resolver) Cookies to be
interoperable across different implementations. Each client need
only be able to recognize its own cookies. However, this document
does contain recommendations for constructing Client Cookies in a
Client protecting fashion.
1.1. Contents of this document
Section Section 2 summarises the changes to [RFC7873].
In Section Section 3 suggestions for constructing a Client Cookie are
given.
In Section Section 4 instructions for constructing a Server Cookie
are given.
In Section Section 5 instructions on updating Server Secrets are
given.
In Section Section 6 the different hash functions usable for DNS
Cookie construction are listed. [FNV] and HMAC-SHA-256-64 [RFC6234]
are deprecated and [SipHash-2.4] is introduced as a REQUIRED hash
function for server side DNS Cookie implementations.
IANA considerations are in Section 7.
Acknowledgements are in Appendix A.
Test vectors are in Appendix B.
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1.2. Definitions
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.
o "IP Address" is used herein as a length independent term covering
both IPv4 and IPv6 addresses.
2. Changes to [RFC7873]
In its Appendices A.1 and B.1, [RFC7873] provides example "simple"
algorithms for computing Client and Server Cookies, respectively.
These algorithms MUST NOT be used as the resulting cookies are too
weak when evaluated against modern security standards.
In its Appendix B.2, [RFC7873] provides an example "more complex"
server algorithm. This algorithm is replaced by the interoperable
specification in Section 4 of this document, which MUST be used by
Server Cookie implementations.
This document has suggestions on Client Cookie construction in
Section 3. The previous example in Appendix A.2 of [RFC7873] is NOT
RECOMMENDED.
3. Constructing a Client Cookie
The Client Cookie is a cryptographic nonce and should be treated as
such. For simplicity, it can be calculated from Server IP Address,
and a Client Secret known only to the Client that is changed whenever
an IP address previously used by the Client is no longer available.
The Client Cookie SHOULD have at least 64-bits of entropy.
Except for when the Client IP address changes, there is no need to
change the Client Secret often if a secure pseudorandom function
(like [SipHash-2.4]) is used. It is reasonable to change the Client
secret then only if it has been compromised or after a relatively
long period of time such as no longer than a year.
It is RECOMMENDED but not required that the following pseudorandom
function be used to construct the Client Cookie:
Client-Cookie = MAC_Algorithm(
Server IP Address, Client Secret )
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Previously, the recommended algorithm to compute the Client Cookie
included Client IP Address as an input to the MAC_Algorithm.
However, when implementing the DNS Cookies, several DNS vendors found
impractical to include the Client IP as the Client Cookie is
typically computed before the Client IP address is known. Therefore,
the requirement to put Client IP address as input was removed.
However, for privacy reasons, in order to prevent tracking of devices
across links and to not circumvent IPv6 Privacy Extensions [RFC4941],
Clients MUST NOT re-use a Client or Server Cookie after the Client IP
address has changed.
The Client IP address is available on the UDP socket when it receives
the Server Cookie and should be registered alongside the Server
Cookie. In subsequent queries to the Server with that Server Cookie,
the socket MUST be bound to the Client IP address that was also used
(and registered) when it received the Server Cookie. Failure to bind
must result in a new Client Cookie, which, for the method described
in this section means a new Client Secret.
4. Constructing a Server Cookie
The Server Cookie is effectively a Message Authentication Code (MAC)
and should be treated as such. The Server Cookie is calculated from
the Client Cookie, a series of Sub-Fields specified below, the Client
IP address, and a Server Secret known only to the servers responding
on the same address in an anycast set.
Changing the Server Secret regularly is RECOMMENDED but, when a
secure pseudorandom function is used, it need not be changed too
frequent. For example once a month would be adequate. See Section 5
on operator and implementation guidelines for updating a Server
Secret.
The 128-bit Server Cookie consists of Sub-Fields: a 1 octet Version
Sub-Field, a 3 octet Reserved Sub-Field, a 4 octet Timestamp Sub-
Field and an 8 octet Hash Sub-Field.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Version | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Timestamp |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Hash |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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4.1. The Version Sub-Field
The Version Sub-Field prescribes the structure and Hash calculation
formula. This document defines Version 1 to be the structure and way
to calculate the Hash Sub-Field as defined in this Section.
4.2. The Reserved Sub-Field
The value of the Reserved Sub-Field is reserved for future versions
of Server Side Cookie construction. On construction it SHOULD be set
to zero octets. On Server Cookie verification the server MUST NOT
enforce those fields to be zero and the Hash should be computed with
the received value as described in Section 4.4.
4.3. The Timestamp Sub-Field
The Timestamp value prevents Replay Attacks and MUST be checked by
the server to be within a defined period of time. The DNS Server
SHOULD allow Cookies within 1 hour period in the past and 5 minutes
into the future to allow operation of low volume clients and some
limited time skew between the DNS servers in the anycast.
The Timestamp value specifies a date and time in the form of a 32-bit
unsigned number of seconds elapsed since 1 January 1970 00:00:00 UTC,
ignoring leap seconds, in network byte order. All comparisons
involving these fields MUST use "Serial number arithmetic", as
defined in [RFC1982]
The DNS Server SHOULD generate a new Server Cookie at least if the
received Server Cookie from the Client is more than half an hour old.
4.4. The Hash Sub-Field
It's important that all the DNS servers use the same algorithm for
computing the Server Cookie. This document defines the Version 1 of
the Server Side algorithm to be:
Hash = SipHash2.4(
Client Cookie | Version | Reserved | Timestamp | Client-IP,
Server Secret )
where "|" indicates concatenation.
Notice that Client-IP is used for hash generation even though it's
not included in the cookie value itself. Client-IP can be either 4
bytes for IPv4 or 16 bytes for IPv6.
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The Server Secret MUST be configurable to make sure that servers in
an anycast network return consistent results.
5. Updating the Server Secret
All servers in an anycast group must be able to verify the Server
Cookies constructed by all other servers in that anycast set at all
times. Therefore it is vital that the Server Secret is shared among
all servers before it us used to generate Server Cookies.
Also, to maximize maintaining established relationships between
clients and servers, an old Server Secret should be valid for
verification purposes for a specific period.
To facilitate this, deployment of a new Server Secret MUST be done in
three stages:
Stage 1
The new Server Secret is deployed on all the servers in an anycast
set by the operator.
Each server learns the new Server Secret, but keeps using the
previous Server Secret to generate Server Cookies.
Server Cookies constructed with the both the new Server Secret and
with the previous Server Secret are considered valid when
verifying.
After stage 1 completed, all the servers in the anycast set have
learned the new Server Secret, and can verify Server Cookies
constructed with it, but keep generating Server Cookies with the
old Server Secret.
Stage 2
This stage is initiated by the operator after the Server Cookie is
present on all members in the anycast set.
When entering Stage 2, servers start generating Server Cookies
with the new Server Secret. The previous Server Secret is not yet
removed/forgotten about.
Server Cookies constructed with the both the new Server Secret and
with the previous Server Secret are considered valid when
verifying.
Stage 3
This stage is initiated by the operator when it can be assumed
that most clients have learned the new Server Secret.
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With this stage, the previous Server Secret can be removed and
MUST NOT be used anymore for verifying.
We RECOMMEND the operator to wait at least a period to be the
longest TTL in the zones served by the server plus half an hour
after it initiated Stage 2, before initiating Stage 3.
The operator SHOULD wait at least longer than the period clients
are allowed to use the same Server Cookie, which SHOULD be half an
hour, see Section 4.3.
6. Cookie Algorithms
[SipHash-2.4] is a pseudorandom function suitable as Message
Authentication Code. This document REQUIRES compliant DNS Server to
use SipHash-2.4 as a mandatory and default algorithm for DNS Cookies
to ensure interoperability between the DNS Implementations.
The construction method and pseudorandom function used in calculating
and verifying the Server Cookies are determined by the initial
version byte and by the length of the Server Cookie. Additional
pseudorandom or construction algorithms for Server Cookies might be
added in the future.
7. IANA Considerations
IANA is requested to create a registry on the "Domain Name System
(DNS) Parameters" IANA web page as follows:
Registry Name: DNS Server Cookie Methods
Assignment Policy: Expert Review
Reference: [this document], [RFC7873]
Note: Server Cookie method (construction and pseudorandom algorithm)
are determined by the Version in the first byte of the Cookie and by
the Cookie size. Server Cookie size is limited to the inclusive
range of 8 to 32 bytes.
Implementation recommendations for Cookie Algorithms [DNSCOOKIE-
IANA]:
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+---------+-------+---------------------------------------+
| Version | Size | Method |
+---------+-------+---------------------------------------+
| 0 | 8-32 | reserved |
| 1 | 8-15 | unassiged |
| 1 | 16 | SipHash-2.4 [this document] Section 4 |
| 1 | 17-32 | unassigned |
| 2-239 | 8-32 | unassigned |
| 240-254 | 8-32 | private use |
| 255 | 8-32 | reserved |
+---------+-------+---------------------------------------+
8. References
8.1. Normative References
[RFC1982] Elz, R. and R. Bush, "Serial Number Arithmetic", RFC 1982,
DOI 10.17487/RFC1982, August 1996,
<https://www.rfc-editor.org/info/rfc1982>.
[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>.
[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>.
[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>.
[SipHash-2.4]
Aumasson, J. and D. Bernstein, "SipHash: a fast short-
input PRF", 2012, <https://131002.net/siphash/>.
8.2. Informative References
[FNV] Fowler, G., Noll, L., Vo, K., Eastlake, D., and T. Hansen,
"The FNV Non-Cryptographic Hash Algorithm",
<https://datatracker.ietf.org/doc/draft-eastlake-fnv>.
[RFC6234] Eastlake 3rd, D. and T. Hansen, "US Secure Hash Algorithms
(SHA and SHA-based HMAC and HKDF)", RFC 6234,
DOI 10.17487/RFC6234, May 2011,
<https://www.rfc-editor.org/info/rfc6234>.
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Appendix A. Acknowledgements
Thanks to Witold Krecicki and Pieter Lexis for valuable input,
suggestions and text and above all for implementing a prototype of an
interoperable DNS Cookie in Bind9, Knot and PowerDNS during the
hackathon of IETF104 in Prague. Thanks for valuable input and
suggestions go to Ralph Dolmans, Bob Harold, Daniel Salzman, Martin
Hoffmann, Mukund Sivaraman, Petr Spacek, Loganaden Velvindron, Bob
Harold and Philip Homburg
Appendix B. Test vectors
B.1. Learning a new Server Cookie
A resolver (client) sending from IPv4 address 198.51.100.100, sends a
query for "example.com" to an authoritative server listening on
192.0.2.53 from which it has not yet learned the server cookie.
The DNS requests and replies shown in this Appendix, are in a "dig"
like format. The content of the DNS COOKIE Option is shown in
hexadecimal format after "; COOKIE:".
;; Sending:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 57406
;; flags:; QUERY: 1, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 1
;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
; COOKIE: 2464c4abcf10c957
;; QUESTION SECTION:
;example.com. IN A
;; QUERY SIZE: 52
The authoritative nameserver (server) is configured with the
following secret: e5e973e5a6b2a43f48e7dc849e37bfcf (as hex data).
It receives the query at Wed Jun 5 10:53:05 UTC 2019.
The content of the DNS COOKIE Option that the server will return is
shown below in hexadecimal format after "; COOKIE:"
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;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 57406
;; flags: qr aa; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1
;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
; COOKIE: 2464c4abcf10c957010000005cf79f111f8130c3eee29480 (good)
;; QUESTION SECTION:
;example.com. IN A
;; ANSWER SECTION:
example.com. 86400 IN A 192.0.2.34
;; Query time: 6 msec
;; SERVER: 192.0.2.53#53(192.0.2.53)
;; WHEN: Wed Jun 5 10:53:05 UTC 2019
;; MSD SIZE rcvd: 84
B.2. The same client learning a renewed (fresh) Server Cookie
40 minutes later, the same resolver (client) queries the same server
for for "example.org" :
;; Sending:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 50939
;; flags:; QUERY: 1, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 1
;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
; COOKIE: 2464c4abcf10c957010000005cf79f111f8130c3eee29480
;; QUESTION SECTION:
;example.org. IN A
;; QUERY SIZE: 52
The authoritative nameserver (server) now generates a new Server
Cookie. The server SHOULD do this because it can see the Server
Cookie send by the client is older than half an hour Section 4.3, but
it is also fine for a server to generate a new Server Cookie sooner,
or even for every answer.
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;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 50939
;; flags: qr aa; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1
;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
; COOKIE: 2464c4abcf10c957010000005cf7a871d4a564a1442aca77 (good)
;; QUESTION SECTION:
;example.org. IN A
;; ANSWER SECTION:
example.org. 86400 IN A 192.0.2.34
;; Query time: 6 msec
;; SERVER: 192.0.2.53#53(192.0.2.53)
;; WHEN: Wed Jun 5 11:33:05 UTC 2019
;; MSD SIZE rcvd: 84
B.3. Another client learning a renewed Server Cookie
Another resolver (client) with IPv4 address 203.0.113.203 sends a
request to the same server with a valid Server Cookie that it learned
before (at Wed Jun 5 09:46:25 UTC 2019). Note that the Server Cookie
has Reserved bytes set, but is still valid with the configured
secret; the Hash part is calculated taking along the Reserved bytes.
;; Sending:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 34736
;; flags:; QUERY: 1, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 1
;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
; COOKIE: fc93fc62807ddb8601abcdef5cf78f71a314227b6679ebf5
;; QUESTION SECTION:
;example.com. IN A
;; QUERY SIZE: 52
The authoritative nameserver (server) replies with a freshly
generated Server Cookie for this client conformant with this
specification; so with the Reserved bits set to zero.
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;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 34736
;; flags: qr aa; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1
;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
; COOKIE: fc93fc62807ddb86010000005cf7a9acf73a7810aca2381e (good)
;; QUESTION SECTION:
;example.com. IN A
;; ANSWER SECTION:
example.com. 86400 IN A 192.0.2.34
;; Query time: 6 msec
;; SERVER: 192.0.2.53#53(192.0.2.53)
;; WHEN: Wed Jun 5 11:38:20 UTC 2019
;; MSD SIZE rcvd: 84
B.4. IPv6 query with rolled over secret
The query below is from a client with IPv6 address
2001:db8:220:1:59de:d0f4:8769:82b8 to a server with IPv6 address
2001:db8:8f::53. The client has learned a valid Server Cookie before
when the Server had secret: dd3bdf9344b678b185a6f5cb60fca715. The
server now uses a new secret, but it can still validate the Server
Cookie provided by the client as the old secret has not expired yet.
;; Sending:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 6774
;; flags:; QUERY: 1, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 1
;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
; COOKIE: 22681ab97d52c298010000005cf7c57926556bd0934c72f8
;; QUESTION SECTION:
;example.net. IN A
;; QUERY SIZE: 52
The authoritative nameserver (server) replies with a freshly
generated server cookie for this client with its new secret:
445536bcd2513298075a5d379663c962
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;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 6774
;; flags: qr aa; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1
;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
; COOKIE: 22681ab97d52c298010000005cf7c609a6bb79d16625507a (good)
;; QUESTION SECTION:
;example.net. IN A
;; ANSWER SECTION:
example.net. 86400 IN A 192.0.2.34
;; Query time: 6 msec
;; SERVER: 2001:db8:8f::53#53(2001:db8:8f::53)
;; WHEN: Wed Jun 5 13:36:57 UTC 2019
;; MSD SIZE rcvd: 84
Authors' Addresses
Ondrej Sury
Internet Systems Consortium
CZ
Email: ondrej@isc.org
Willem Toorop
NLnet Labs
Science Park 400
Amsterdam 1098 XH
Netherlands
Email: willem@nlnetlabs.nl
Donald E. Eastlake 3rd
Futurewei Technologies
1424 Pro Shop Court
Davenport FL 33896
USA
Phone: +1-508-333-2270
Email: d3e3e3@gmail.com
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Mark Andrews
Internet Systems Consortium
950 Charter Street
Redwood City CA 94063
USA
Email: marka@isc.org
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