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Versions: 00 01

DNSOP Working Group                                            R. Bellis
Internet-Draft                                                  A. Clegg
Intended status: Standards Track                                     ISC
Expires: September 26, 2019                                  P. van Dijk
                                                                PowerDNS
                                                          March 25, 2019


                             DNS EDNS Tags
                    draft-bellis-dnsop-edns-tags-01

Abstract

   This document describes EDNS Tags, a mechanism by which DNS clients
   and servers can transmit an opaque data field which has no defined
   semantic meaning other than as previously agreed between the client
   and server.

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-
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   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 September 26, 2019.

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




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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   2
   3.  Description . . . . . . . . . . . . . . . . . . . . . . . . .   3
     3.1.  Packet Validation Rules . . . . . . . . . . . . . . . . .   3
     3.2.  Error Handling  . . . . . . . . . . . . . . . . . . . . .   3
     3.3.  Wire Format . . . . . . . . . . . . . . . . . . . . . . .   4
       3.3.1.  EDNS-Client-Tag . . . . . . . . . . . . . . . . . . .   4
       3.3.2.  EDNS-Server-Tag . . . . . . . . . . . . . . . . . . .   4
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   5.  Implementation status . . . . . . . . . . . . . . . . . . . .   5
   6.  Privacy Considerations  . . . . . . . . . . . . . . . . . . .   5
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   5
   9.  Normative References  . . . . . . . . . . . . . . . . . . . .   5
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Introduction

   This document describes EDNS Tags, a mechanism by which DNS clients
   and servers [RFC1034] can transmit an opaque data field which has no
   defined semantic meaning other than as previously agreed between the
   client and server operators.

   The tag is a single 16 bit field stored within the RDATA of an
   EDNS(0) OPT RR as described in [RFC6891].

   Two EDNS options are defined to allow for the detection of servers
   that incorrectly echo responses verbatim.  The EDNS-Client-Tag option
   may only appear in client requests, and the EDNS-Server-Tag may only
   appear in responses from servers.

2.  Terminology

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








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3.  Description

   The values of the individual bits within a tag are not defined to
   have any semantic meaning in this specification.  Their
   interpretation is defined entirely by out-of-band bilateral agreement
   between client and server operators.

   Operators are free to partition the bits within that field as they
   see fit; for example it could be used to transmit up to 16 separate
   boolean flags, or perhaps to transmit a 10 bit numeric value combined
   a 2 bit value and four boolean flags.

   The intended mode of operation is that the value of a bit (or range
   of bits) could be tested in access control lists or any other such
   policy control mechanism.

   Possible use cases for EDNS-Client-Tags include:

   o  client-controlled selection of a DNS-based security filter

   o  marking a packet passing through a proxy with transport-related
      information

   Use cases for EDNS-Server-Tags are still to be determined.  The
   option is specified here for symmetry and in anticipation of new use
   cases being discovered.  The semantic definitions for EDNS-Client-Tag
   and EDNS-Server-Tag values MAY be different; they need not be
   symmetrical.

3.1.  Packet Validation Rules

   The OPT RR in a DNS request packet (QR = 0) MUST NOT contain an EDNS-
   Server-Tag option.  A request packet MUST NOT contain more than one
   EDNS-Client-Tag option.

   The OPT RR in a DNS response packet (QR = 1) MUST NOT contain an
   EDNS-Client-Tag option.  A response packet MUST NOT contain more than
   one EDNS-Server-Tag option.

   An EDNS-Server-Tag option MUST NOT be sent unless the corresponding
   client query contained an EDNS-Client-Tag option.

3.2.  Error Handling

   Clients MUST discard any response packet that breaches any applicable
   packet validation rule.





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   Servers MUST respond with a FORMERR in accordance with Section 7 of
   [RFC6891] on receipt of a request that breaches any applicable packet
   validation rule.

3.3.  Wire Format

   The format of the EDNS options are as follows, to be stored within
   the RDATA of an OPT RR as specified in [RFC6891]:

3.3.1.  EDNS-Client-Tag

                   +0 (MSB)                            +1 (LSB)
      +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
   0: |                       OPTION-CODE (TBD1)                      |
      +---+---+---+---+---+---+---+---|---+---+---+---+---+---+---+---+
   2: |                       OPTION-LENGTH (2)                       |
      +---+---+---+---+---+---+---+---|---+---+---+---+---+---+---+---+
   4: |                        CLIENT-TAG-DATA                        |
      +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+

   OPTION-CODE: The option code identifier (TBD1).

   OPTION-LENGTH: Size (in octets) of OPTION-DATA.  MUST be 2.

   CLIENT-TAG-DATA: The tag field sent from client to server.

3.3.2.  EDNS-Server-Tag

                   +0 (MSB)                            +1 (LSB)
      +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
   0: |                       OPTION-CODE (TBD2)                      |
      +---+---+---+---+---+---+---+---|---+---+---+---+---+---+---+---+
   2: |                       OPTION-LENGTH (2)                       |
      +---+---+---+---+---+---+---+---|---+---+---+---+---+---+---+---+
   4: |                        SERVER-TAG-DATA                        |
      +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+

   OPTION-CODE: The option code identifier (TBD2).

   OPTION-LENGTH: Size (in octets) of OPTION-DATA.  MUST be 2.

   SERVER-TAG-DATA: The tag field sent from server to client.

4.  Security Considerations

   Client tags are under the control of the client software and as such
   (and in the absence of any other mechanism to authenticate the
   client's identity) this mechanism is not appropriate for applications



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   where the DNS server operator wishes to contractually differentiate
   service based on the interpretation of the tag's value.

5.  Implementation status

   TBC.

6.  Privacy Considerations

   Tags are opaque fields that encode only a limited amount of
   information.  The size of the data field in this specification is
   chosen to offer a compromise between offering sufficient content to
   be technically useful while also limiting the scope for it to be used
   to transmit Personally Identifiable Information.

7.  IANA Considerations

   IANA has assigned the following EDNS(0) Option Codes:

   Value    Name                  Status         Reference
   ----------------------------------------------------------
   TBD1     EDNS-Client-Tag       Standard       RFCXXXX
   TBD2     EDNS-Server-Tag       Standard       RFCXXXX

   << Note to IANA - please assign an even value to TBD1, and the next
   consecutive odd value to TBD2.  This allows the least-significant bit
   of the option value to be compared against the packet's QR bit >>

8.  Acknowledgements

   The authors wish to particularly thank Brian Conry, Peter van Dijk
   and Matthijs Mekking for early review and feedback on this document.

9.  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>.

   [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>.

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



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   [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>.

Authors' Addresses

   Ray Bellis
   Internet Systems Consortium, Inc.
   950 Charter Street
   Redwood City  CA 94063
   USA

   Phone: +1 650 423 1200
   Email: ray@isc.org


   Alan Clegg
   Internet Systems Consortium, Inc.
   950 Charter Street
   Redwood City  CA 94063
   USA

   Phone: +1 650 423 1200
   Email: aclegg@isc.org


   Peter van Dijk
   PowerDNS.COM B.V.
   Den Haag
   The Netherlands

   Email: peter.van.dijk@powerdns.com



















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