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Versions: (draft-sury-toorop-dnsop-server-cookies) 00 01 02

DNSOP Working Group                                              O. Sury
Internet-Draft                               Internet Systems Consortium
Updates: 7873 (if approved)                                    W. Toorop
Intended status: Standards Track                              NLnet Labs
Expires: May 21, 2020                                    D. Eastlake 3rd
                                                  Futurewei Technologies
                                                              M. Andrews
                                             Internet Systems Consortium
                                                       November 18, 2019


         Interoperable Domain Name System (DNS) Server Cookies
                   draft-ietf-dnsop-server-cookies-02

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 21, 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.  Security and Privacy Considerations . . . . . . . . . . . . .   9
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  10
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  10
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  10
   Appendix A.  Acknowledgements . . . . . . . . . . . . . . . . . .  11
   Appendix B.  Test vectors . . . . . . . . . . . . . . . . . . . .  11
     B.1.  Learning a new Server Cookie  . . . . . . . . . . . . . .  11
     B.2.  The same client learning a renewed (fresh) Server Cookie   12
     B.3.  Another client learning a renewed Server Cookie . . . . .  13
     B.4.  IPv6 query with rolled over secret  . . . . . . . . . . .  14
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  15

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



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   attackers.  This document specifies a means of producing
   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.

   Privacy and Security Considerations in Section 8.




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   Acknowledgements are in Appendix A.

   Test vectors are in Appendix B.

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.  It is RECOMMENDED to create a new Client Cookie for each new
   upstream server a Client connects to.  The Client Cookie SHOULD have
   at least 64-bits of entropy.

   When a Server does not support DNS Cookies, the Client MUST NOT send
   the same Client Cookie to that same Server again.  Instead, it is
   recommended that the Client does not send a Client Cookie to that
   Server for a certain period, like for example five minutes, before it
   retries with a new Client Cookie.

   When a Server does support DNS Cookies, the Client should store the
   Client Cookie alongside the Server Cookie it registered for that
   Server.




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   Except for when the Client IP address changes, there is no need to
   change the Client Cookie often.  It is reasonable to change the
   Client Cookie then only if it has been compromised or after a
   relatively long period of time such as no longer than a year.  Client
   Cookies are not expected to survive a program restart.

                    Client-Cookie = 64 bits of entropy

   Previously, the recommended algorithm to compute the Client Cookie
   included Client IP Address as an input to a hashing function.
   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.

   One way to track Client IP addresses, is to register the Client IP
   address alongside the Server Cookie when it receives the Server
   Cookie.  In subsequent queries to the Server with that Server Cookie,
   the socket MAY be bound to the Client IP address that was also used
   (and registered) when it received the Server Cookie.  Failure to bind
   MUST then result in a new Client Cookie.

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.







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      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                              |
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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:




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      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.

   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.





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      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.

      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.



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   Implementation recommendations for Cookie Algorithms [DNSCOOKIE-
   IANA]:

        +---------+-------+---------------------------------------+
        | 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.  Security and Privacy Considerations

   DNS Cookies 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.  They provide no
   protection against on-path adversaries that can observe the plaintext
   DNS traffic.  An on-path adversary that can observe a Server Cookie
   for a client and server interaction, can use that Server Cookie for
   amplification and denial-of-service forgery attacks for the lifetime
   of the Server Cookie.

   In [RFC7873] it was RECOMMENDED to construct a Client Cookie by using
   a pseudorandom function of the Client IP Address, the Server IP
   Address, and a secret quantity known only to the client.  The Client
   IP Address was included to ensure that a client could not be tracked
   if its IP Address changes due to privacy mechanisms or otherwise.

   In this document, we changed Client Cookie construction to be just 64
   bits of entropy newly created for each new upstream server the client
   connects to.  As a consequence additional care needs to be taken to
   prevent tracking of clients.  To prevent tracking, a new Client
   Cookie for a server MUST be created whenever the Client IP Address
   changes.

   Unfortunately, tracking Client IP Address Changes is impractical with
   servers that do not support DNS Cookies.  To prevent tracking of
   clients with non DNS Cookie supporting servers, a client MUST NOT
   send a previously sent Client Cookie.  To prevent the creation of a
   new Client Cookie for each query to an non DNS Cookies supporting
   server, it is RECOMMENDED to not send a Client Cookie to that server
   for a certain period, like for example five minute.

   Summarizing:



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   o  In order to provide minimal authentication, a client MUST use a
      different Client Cookie for each different Server IP Address.

   o  To prevent tracking of clients, a new Client Cookie MUST be
      created when the Client IP Address changes.

   o  To prevent tracking of clients for a non DNS Cookie supporting
      server, a client MUST NOT send a previously sent Client Cookie to
      that server, unless it can track Client IP Address changes for
      those servers too.

   Besides the Client Cookie construction, this update on [RFC7873] does
   not introduce any new characteristics to DNS Cookies operations and
   the Security Considerations section of [RFC7873] still applies.

9.  References

9.1.  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/>.

9.2.  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>.






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   [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>.

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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