INTERNET-DRAFT                                    Donald E. Eastlake 3rd
                                                   Motorola Laboratories
Expires: April 2007                                         October 2006

                    Domain Name System (DNS) Cookies
                    ------ ---- ------ ----- -------

Status of This Document

   By submitting this Internet-Draft, each author represents that any
   applicable patent or other IPR claims of which he or she is aware
   have been or will be disclosed, and any of which he or she becomes
   aware will be disclosed, in accordance with Section 6 of BCP 79.

   This draft is intended to be become a Proposed Standard RFC.
   Distribution of this document is unlimited. Comments should be sent
   to the author or the DNSEXT working group mailing list

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute working documents as Internet-

   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."

   The list of current Internet-Drafts can be accessed at

   The list of Internet-Draft Shadow Directories can be accessed at

   DNS cookies are a light-weight DNS transaction security mechanism.
   They provides limited protection to DNS servers and resolvers against
   a variety of increasingly common denial-of-service and cache
   poisoning attacks by off-path attackers.

Copyright Notice

   Copyright (C) The Internet Society (2006).

D. Eastlake 3rd                                                 [Page 1]

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Table of Contents

      Status of This Document....................................1
      Copyright Notice...........................................1

      Table of Contents..........................................2

      1. Introduction............................................3
      1.1 Contents of This Document..............................3
      1.2 Definitions............................................3
      2. Threats Considered......................................4
      2.1 Denial-of-Service Attacks..............................4
      2.1.1 DNS Server Denial-of-Service.........................4
      2.1.2 Selected Host Denial-of-Service......................5
      2.2 Cache Poisoning Attacks................................5
      3. Comments on Existing DNS Security.......................5
      4. The COOKIE OPT option...................................6
      4.1 Resolver Cookies.......................................7
      4.2 Server Cookies.........................................8
      5. General Policies and Implementation.....................8
      5.1 Resolver Policies and Implementation...................9
      5.2 Server Policies and Implementation.....................9
      5.3 Implementation Requirements...........................10
      6. NAT and AnyCast Considerations.........................10
      7. IANA Considerations....................................12
      8. Security Considerations................................12
      9. Copyright and Disclaimer...............................13
      10. Normative References..................................13
      11. Informative References................................14

      Author's Address..........................................15
      Additional IPR Provisions.................................15
      Expiration and File Name..................................15

D. Eastlake 3rd                                                 [Page 2]

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1. Introduction

   The Domain Name System (DNS) provides a replicated distributed
   database which stores "resource records" (RRs) under hierarchical
   domain names.  DNS data is structured into CLASSes and zones which
   can be independently maintained.  See [STD13], [RFC2181] familiarity
   with which is assumed.

   As with many core Internet protocols, DNS was designed at a time when
   the Internet had only a small pool of trusted users. As the Internet
   has exploded to a global information utility the DNS has increasingly
   been subject to abuse and been used as a vector for abuse.

   This document describes DNS cookies, a light-weight DNS transaction
   security mechanism specified as an OPT [RFC2671] option. They
   provides limited protection to DNS servers and resolvers against a
   variety of increasingly common denial-of-service and cache poisoning
   attacks by off-path attackers.

1.1 Contents of This Document

   In Section 2, we discuss the threats against which DNS cookies
   provides some protection.

   Section 3 describes existing DNS security mechanisms and why they are
   not adequate substitutes for DNS cookies.

   Section 4 describes the COOKIE OPT option including recommendations
   for calculating Resolver and Server Cookies.

   Section 5 describes the processing of COOKIE OPT optionby resolvers
   and server and policies for such processing.

   Section 6 discusses some NAT and anycast related DNS Cookies design

   Sections 7 and 8 describe IANA and Security Considerations.

1.2 Definitions

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in [RFC2119].

   An "off-path attacker", for a particular DNS resolver and server, is
   defined as an attacker which cannot observe the legitimate plain text

D. Eastlake 3rd                                                 [Page 3]

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   DNS requests and responses between that resolver and server.

   "Soft state" indicates information learned or derived by a host which
   may be discarded when indicated by the policies of that host. For
   example, it could be discarded after a period of time or when storage
   for caching such data becomes full. If operations requiring that soft
   state continue after it has been discarded, it will be automatically
   re-generated, albeit at some cost.

   "Silently discarded" indicates that there are no DNS protocol message
   consequences; however, it is RECOMMENDED that appropriate debugging
   network management facilities be included in implementations, such as
   a counter of the occurrences of each type of such events.

   The term "IP address" is used herein in a length independent manner
   and refers interchangeably to IPv4 and IPv6 addresses.

2. Threats Considered

   DNS cookies are intended to provide significant but limited
   protection against certain denial-of-service and cache poisoning
   attacks by off-path attackers described below.

2.1 Denial-of-Service Attacks

   The normal form of the denial-of-service attacks considered herein is
   to send DNS requests with forged source IP addresses to a server. The
   intent can be to attack that server or a selected host as described

2.1.1 DNS Server Denial-of-Service

   DNS requests that are accepted cause work on the part of DNS servers.
   This is particularly true for recursive servers which may issue one
   or more requests and process the responses thereto in order to
   determine their response to the initial query. And the situation is
   even worse for recursive servers implementing DNSSEC [RFC4033],
   [RFC4034], [RFC4035] because they may be induced to perform
   burdensome public key cryptographic computations in attempts to
   verify the authenticity of data they retrieve in trying to answer the

   While the burden cause by such requests is not dependent on a forged
   IP source address, the use of such addresses makes

D. Eastlake 3rd                                                 [Page 4]

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   +  the source of the requests causing the denial-of-service requests
      to be harder to find and
   +  administrative restriction of the IP addresses from which such
      requests should be honored harder to enforce.

2.1.2 Selected Host Denial-of-Service

   Request with a forged IP address causes a response to be sent to that
   forged IP address. Thus the forging of many such requests can,
   indirectly, result in enough traffic being sent to the forged IP
   address to interfere with service to the host at the IP address.
   Furthermore, it is generally easy in the DNS to create short requests
   that produce much longer responses. Thus a DNS server can be used as
   not only a way to obscure the true source of an attack but as a
   traffic amplifier to make the attack more effective.

   Use of DNS cookies severely limits the traffic amplification that can
   be obtained by attackers off path for the server and the attacked
   host. Enforced DNS cookies would make it hard for an off path
   attacker to cause any more than a brief error response to be send to
   a forged IP address.  Furthermore, DNS cookies make it more effective
   to implement a rate limiting scheme for bad DNS cookie error response
   from the server. Such a scheme would further restrict selected host
   denial-of-service traffic from that server.

2.2 Cache Poisoning Attacks

   The form of the cache poisoning attacks considered is to send forged
   replies to a resolver. Modern network speeds for well connected hosts
   are such that, by forging replies from the IP addresses of heavily
   used DNS servers and for popular names to a heavily used resolver,
   there can be an unacceptably high probability of randomly coming up
   with a reply that will be accepted and cause false DNS information to
   be cached by that resolver. This can be used to facilitate phishing
   attacks and other diversion of legitimate traffic to a compromised or
   malicious host such as a web server.

3. Comments on Existing DNS Security

   Two forms of security have been added to DNS:

   The first, called DNSSEC and described in [RFC4033], [RFC4034], and
   [RFC4035], provides data origin authentication and authenticated
   denial of existence. It is being deployed very slowly and, in any

D. Eastlake 3rd                                                 [Page 5]

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   case, can make some denial-of-service attacks worse because of the
   high cryptographic computational load it can require and the
   increased size in DNS packets that it can produces.

   The second form of security which has been added to DNS provides
   "transaction" security through TSIG [RFC2845] or SIG(0) [RFC2931].
   TSIG could provide near perfect protection against the attacks for
   which DNS cookies provide weak and incomplete protection; however,
   TSIG is hard to deploy in the general Internet because of the burden
   it imposes of pre-agreement and key distribution between pairs of
   resolvers and servers and because it requires time synchronization
   between resolver and server.

   TKEY [RFC2930] can solve the problem of key distribution for TSIG but
   some modes of TKEY impose substantial cryptographic computations
   loads and can be dependent on the deployment of DNSSEC.

   SIG(0) provides less protection than TSIG or, in one way, even DNS
   cookies, because it does not authentication requests, only complete
   transactions.  In any case, it also depends on the deployment of
   DNSSEC and requires computationally burdensome public key
   cryptographic operations.

   Thus, none of the previous forms of DNS security are a suitable
   substitute for DNS cookies, which provide light weight transaction
   authentication of DNS requests and responses with no requirement for

4. The COOKIE OPT option

   COOKIE is an OPT RR [RFC2671] option that can be included once in the
   RDATA portion of an OPT RR in DNS requests and responses.

   The option is encoded into 22 bytes as shown below.

D. Eastlake 3rd                                                 [Page 6]

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                         1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 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
    |       OPTION-CODE TBD         |     OPTION-LENGTH = 18        |
    |                   Resolver Cookie upper half                  |
    |                   Resolver Cookie lower half                  |
    |                    Server Cookie upper half                   |
    |                    Server Cookie lower half                   |
    |           Error Code          |

   The Resolver and Server Cookies are stored in network byte order and
   are determined as described below.

   The Error Code field MUST BE zero in requests and in responses unless
   the response is communicating a DNS cookie error. Three values are
   possible for Error Code: NOCOOKIE and BADCOOKIE which occur with a
   Refused RCODE in the DNS response header, and MANYCOOKIE which occurs
   with a FormErr RCODE in the DNS header. More information on the
   generation of error response appears in Section 5 below.

4.1 Resolver Cookies

   The Resolver Cookie, when it occurs in an OPT in a DNS response, is
   intended to weakly assure the resolver that the response came from a
   server at the indicated source IP address.

   Servers remember the Resolver Cookie that appears in a query long
   enough to use it in the construction of the COOKIE OPT option in the
   corresponding response if such a COOKIE OPT option is included in
   that response.

   The Resolver Cookie SHOULD be a pseudo-random function of the server
   IP address and a secret quantity known only to the resolver. This
   resolver secret SHOULD have 64 bits of entropy [RFC4086] and MAY be
   changed periodically.  The RECOMMENDED method is the HMAC-MD5-64
   [RFC1321], [RFC2104] of the server IP address and the resolver
   secret. That is

      Resolver Cookie =
      Truncate-64 ( HMAC-MD5 ( Server IP, Resolver Secret ) )

   A resolver MUST NOT use the same Resolver Cookie value for queries to

D. Eastlake 3rd                                                 [Page 7]

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   all servers.

4.2 Server Cookies

   The Server Cookie, when it occurs in a COOKIE OPT option in a query,
   is intended to weakly assure the server that the query legitimately
   came from a resolver at the indicated source IP address that is using
   the indicated Resolver Cookie.

   Resolvers learn Server Cookies and retain them as soft state
   associated with the server IP address. They learn them from the
   Server Cookie that appears in the COOKIE OPT option of a reply that
   also has the correct Resolver Cookie, even if that reply is an error

   The Server Cookie SHOULD be a pseudo-random function of the request
   source IP address, the request Resolver Cookie, and a secret quantity
   known only to the server. This server secret SHOULD have 64 bits of
   entropy [RFC4086] and SHOULD be changed periodically such as daily.
   The RECOMMENDED method is the HMAC-MD5-64 [RFC1321], [RFC2104] of the
   request IP address, the Resolver Cookie, and the server secret. That

      Server Cookie = Truncate-64 (
      HMAC-MD5 ( (Request IP | Resolver Cookie), Server Secret ) )

   where "|" represents concatenation.

   A server MUST NOT use the same Server Cookie value for responses to
   all requests.

5. General Policies and Implementation

   DNS resolvers and servers will adopt one of various policies
   regarding cookies. These policies SHOULD be logically settable on a
   per server IP address basis for resolvers and a per resolver ( IP
   address, Resolver Cookie ) pair for servers.  Thus a resolver can
   have different policies for different servers, based on the server IP
   address. And a server can have different policies for different
   resolvers, based on the resolver IP address and Resolver Cookie. Of
   course, the actual implementation of setting these policies may by
   for blocks or classes of values or use sparse array techniques.

   The policy for each value is either "Disabled", "Enabled", or
   "Enforced" as described below.

D. Eastlake 3rd                                                 [Page 8]

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5.1 Resolver Policies and Implementation

      Never include a COOKIE RR in requests.
      Ignore COOKIE OPT options in responses.

      Always include an OPT RR with a COOKIE option in requests. If a
         cached Server Cookie for the server is not available, the
         Server Cookie field can be set to any value.
      Normally process responses without a COOKIE OPT option.
      Silently ignore responses with more than one COOKIE OPT option.
      Silently ignore responses with one COOKIE OPT option if it has an
         incorrect Resolver Cookie value.
      On receipt of a response with one COOKIE OPT option and it having
         the correct Resolver Cookie value (even if it is a BADCOOKIE
         error response), perform normal response processing, including
         caching the received Server Cookie and MUST change to the
         Enforced policy for DNS requests to that server IP address.
         This policy change SHOULD be treated as soft state with the
         same discard policy as the Server Cookie value for that server.
         On discarding that state information, the policy for that
         server reverts to Enabled.

      Always include a COOKIE OPT option in requests.
      Silently ignore all responses that do not include exactly one
         COOKIE OPT option with it having the correct Resolver Cookie
         value. Normally process responses which do include such a
         COOKIE OPT option.

5.2 Server Policies and Implementation

      Ignore COOKIE OPT options in requests.
      Never include a COOKIE OPT option in responses.

      Normally process requests without a COOKIE OPT option.
      Ignore, other than sending a MANYCOOKIE error response, any
         request with more than one COOKIE OPT option.
      Ignore, other than sending a BADCOOKIE error response, any query
         with one COOKIE OPT option if it has an incorrect Server
      On receipt of a request with a COOKIE OPT option having the
         correct Server Cookie value, perform normal request processing
         and SHOULD adopt the Enforced policy for DNS requests from that
         resolver IP address with that Resolver Cookie in the request.

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         This policy change for that resolver SHOULD be treated as soft
         state. On discarding that state information, the policy for
         that resolver IP and Resolver Cookie pair reverts to enabled.
      Always include a COOKIE OPT option in responses.

      Ignore requests without a COOKIE OPT option or with more than one
         COOKIE OPT option, other than sending a NOCOOKIE or MANYCOOKIE
         error respectively.
      Ignore requests with one COOKIE OPT option if they have an
         incorrect Server Cookie, other than sending a BADCOOKIE error
      If a request has one COOKIE OPT option with a correct Server
         Cookie, perform normal processing of the request.
      Include a COOKIE OPT option in all responses.

5.3 Implementation Requirements

   DNS resolvers and servers MUST implement DNS cookies.

   DNS resolvers SHOULD operate in and be shipped so as to default to
   the Enabled or Enforced mode for all servers.

   DNS servers SHOULD operate in and be shipped so as to default to the
   Enabled or Enforced mode for all resolvers they are willing to

6. NAT and AnyCast Considerations

   In the Classic Internet, DNS Cookies could simply be a pseudo-random
   function of the resolver IP address and a sever secret or the server
   IP address and a resolver secret. You would want to compute the
   Server Cookie that way, so a resolver could cache its Server Cookie
   for a particular server for an indefinitely amount of time and the
   server could easily regenerate and check it. You could consider the
   Resolver Cookie to be a resolver signature over the server IP address
   which the resolver checks in responses and you could extend this
   signature to cover the request ID, for example.

   But we have this wart called NAT [RFC3022], Network Address
   Translation (including therein for the purposes of this document NAT-
   PT [RFC2766], Network Address and Protocol Translation). There is no
   problem with DNS transactions between resolvers and servers behind a
   NAT box using local IP addresses. Nor is there a problem with NAT
   translation of internal addresses to external addresses or
   translations between IPv4 and IPv6 addresses, as long as the address

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   mapping is relatively stable. Should an internal resolver being
   mapped to a particular external IP address change occasionally, the
   disruption is no more than when a resolver rolls-over its DNS COOKIE
   secret. And normally external access to a DNS server behind a NAT box
   is handled by a fixed mapping which forwards externally received DNS
   requests to a specific host.

   However, NAT devices sometimes also map ports. This can cause
   multiple DNS requests and responses from multiple internal hosts to
   be simultaneously mapped to a smaller number of external IP
   addresses, frequently one.  There could be many resolvers behind a
   NAT box that appear to come from the same source IP address to a
   server outside that NAT box..  If one of these were an attacker
   (think Zombie or Botnet), that behind-NAT attacked could get the
   Server Cookie for some server for the outgoing IP address by just
   making some random request to that server. It could then include that
   Server Cookie in the COOKIE RR of requests to the server with the
   forged IP address of the local IP address of some other host and/or
   resolver behind the NAT box. (Attacker possession of this Server
   Cookie will not help in forging responses to cause cache poisoning as
   such responses are protected by the required Resolver Cookie.)

   To fix this potential defect, it is necessary to distinguish
   different resolvers behind a NAT box from the point of view of the
   server. It is for this reason that the Server Cookie is specified as
   a pseudo-random function of both the request source IP address and
   the Resolver Cookie.  From this inclusion of the Resolver Cookie in
   the calculation of the Server Cookie, it follows that a stable
   Resolver Cookie, for any particular server, is needed. If, for
   example, the request ID was included in the calculation of the
   Resolver Cookie, it would normally change with each query to a
   particular server.  This would mean that each query would have to be
   sent twice: first to learn the new Server Cookie based on this new
   Resolver Cookie based on the new ID and then again using this new
   Resolver Cookie to actually get an answer. Thus the input to the
   Resolver Cookie computation must be limited to the server IP address
   and one or more things that change slowly such as the resolver

   In principle, there could be a similar problem for servers, not
   particularly due to NAT but due to mechanisms like anycast which may
   cause queries to a DNS server at an IP address to be delivered to any
   one of several machines. (External queries to a DNS server behind a
   NAT box usually occur via port forwarding such that all such queries
   go to one host.) However, it is impossible to solve this the way the
   similar problem was solved for NATed resolvers; if the Server Cookie
   was included in the calculation of the Resolver Cookie the same way
   the Resolver Cookie is included in the Server Cookie, you would just
   get an almost infinite series of BADCOOKIE errors as a query was
   repeatedly retried.

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   For server accessed via anycast or similar mechanisms to successfully
   support DNS COOKIES, the server clones must either all use the same
   server secret or the mechanism that distributes queries to them must
   cause the queries from a particular resolver to go to a particular
   server for a sufficiently long period of time that extra queries due
   to changes in Server Cookie resulting from accessing different server
   machines are not unduly burdensome. When such anycast accessed
   servers act as recursive servers or otherwise act as resolvers they
   normally use a different unique address to source their queries and
   avoid confusion in the delivery of responses.

   For simplicity, it is recommended that the same server secret be used
   by each set of anycast servers.

7. IANA Considerations

   The OPT option value for COOKIE is TBD.

   Three new RCODES are assigned values above 15:
      NOCOOKIE is assigned the value (TBD, 23 suggested).
      BADCOOKIE is assigned the value (TBD, 24 suggested).
      MANYCOOKIE is assigned the value (TBD, 25 suggested).

8. Security Considerations

   DNS Cookies provide a weak form of authentication of DNS requests and
   responses. In particular, they provide no protection at all against
   "on-path" adversaries; that is, they provide no protection against
   any adversary which can observe the plain text DNS traffic, such as
   an on-path router, bridge, or any device on an on-path shared link
   (unless the DNS traffic in question on that path is appropriately

   For example, if a host is connected via an unsecured IEEE 802.11 link
   (Wi-Fi), any device in the vicinity that could receive and decode the
   802.11 transmissions must be considered "on-path". On the other hand,
   in a similar situation but one where 802.11i security is
   appropriately deployed on the Wi-Fi network nodes, only the Access
   Point via which the host is connecting is "on-path".

   Despite these limitations, use of DNS Cookies on the global Internet
   are expected to provide a reduction in the available launch points
   for the traffic amplification and denial of service attacks described
   in Section 2 above.

   The recommended cryptographic algorithm for use in DNS Cookies is

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   HMAC-MD5-64, that is, the HMAC scheme [RFC2104] using the MD5 hash
   function [RFC1321] with its output truncated to 64-bits. Although MD5
   is now considered to be susceptible to collisions attacks, this does
   not effect the security of HMAC-MD5.

   In light of the weak plain-text token security provided by DNS
   Cookies, stronger cryptography is probably not warranted.  However,
   there is nothing wrong with using, for example, HMAC-SHA256-64
   instead, assuming a DNS processor has adequate computational
   resources available. DNS processors that feel the need for somewhat
   stronger security without a significant increase in computational
   load should consider more frequent changes in their resolver and/or
   server secret; however, this does require more frequent generation of
   a cryptographically strong random number [RFC4086] and a change in a
   server secret will result in a number of BADCOOKIE rejected requests
   from resolvers caching their old Server Cookie.

9. Copyright and Disclaimer

   Copyright (C) The Internet Society (2006).

   This document is subject to the rights, licenses and restrictions
   contained in BCP 78, and except as set forth therein, the authors
   retain all their rights.

   This document and the information contained herein are provided on an

10. Normative References

   [RFC1321] - Rivest, R., "The MD5 Message-Digest Algorithm", RFC 1321,
   April 1992.

   [RFC2104] - Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-
   Hashing for Message Authentication", RFC 2104, February 1997.

   [RFC2119] - Bradner, S., "Key words for use in RFCs to Indicate
   Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2181] - Elz, R. and R. Bush, "Clarifications to the DNS

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   Specification", RFC 2181, July 1997.

   [RFC2671] - Vixie, P., "Extension Mechanisms for DNS (EDNS0)", August

   [RFC4086] - Eastlake, D., 3rd, Schiller, J., and S.  Crocker,
   "Randomness Requirements for Security", BCP 106, RFC 4086, June 2005.

         Mockapetris, P., "Domain names - concepts and facilities", STD
         13, RFC 1034, November 1987.

         Mockapetris, P., "Domain names - implementation and
         specification", STD 13, RFC 1035, November 1987.

11. Informative References.

   [RFC2766] - Tsirtsis, G., P. Srisuresh"Network Address Translation -
   Protocol Translation (NAT-PT)", February 2000.

   [RFC2845] - Vixie, P., Gudmundsson, O., Eastlake 3rd, D., and B.
   Wellington, "Secret Key Transaction Authentication for DNS (TSIG)",
   RFC 2845, May 2000.

   [RFC2930] - Eastlake 3rd, D., "Secret Key Establishment for DNS (TKEY
   RR)", RFC 2930, September 2000.

   [RFC2931] - Eastlake 3rd, D., "DNS Request and Transaction Signatures
   ( SIG(0)s )", RFC 2931, September 2000.

   [RFC3022] - Srisuresh, P. and K. Egevang, "Traditional IP Network
   Address Translator (Traditional NAT)", RFC 3022, January 2001.

   [RFC4033] - Arends, R., Austein, R., Larson, M., Massey, D., and S.
   Rose, "DNS Security Introduction and Requirements", RFC 4033, March

   [RFC4034] - Arends, R., Austein, R., Larson, M., Massey, D., and S.
   Rose, "Resource Records for the DNS Security Extensions", RFC 4034,
   March 2005.

   [RFC4035] - Arends, R., Austein, R., Larson, M., Massey, D., and S.
   Rose, "Protocol Modifications for the DNS Security Extensions", RFC
   4035, March 2005.

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Author's Address

   Donald E. Eastlake 3rd
   Motorola Laboratories
   111 Locke Drive
   Marlborough, MA 01752 USA

   Telephone:   +1-508-786-7554 (w)


Additional IPR Provisions

   The IETF takes no position regarding the validity or scope of any
   Intellectual Property Rights or other rights that might be claimed
   to pertain to the implementation or use of the technology
   described in this document or the extent to which any license
   under such rights might or might not be available; nor does it
   represent that it has made any independent effort to identify any
   such rights.  Information on the procedures with respect to
   rights in RFC documents can be found in BCP 78 and BCP 79.

   Copies of IPR disclosures made to the IETF Secretariat and any
   assurances of licenses to be made available, or the result of an
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   of such proprietary rights by implementers or users of this
   specification can be obtained from the IETF on-line IPR repository

   The IETF invites any interested party to bring to its attention
   any copyrights, patents or patent applications, or other
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   to implement this standard.  Please address the information to the
   IETF at

Expiration and File Name

   This draft expires in April 2007.

   Its file name is draft-eastlake-dnsext-cookies-01.txt

D. Eastlake 3rd                                                [Page 15]