Internet DRAFT - draft-bellis-dnsop-edns-tags
draft-bellis-dnsop-edns-tags
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
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This Internet-Draft will expire on September 26, 2019.
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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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