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Versions: 00                                                            
dnsop                                                         B. Dickson
Internet-Draft
Intended status: Standards Track                        October 15, 2014
Expires: April 18, 2015


              System to transport DNS over HTTP using JSON
                draft-dickson-dnsop-spartacus-system-00

Abstract

   This is the SPARTACUS DNS gateway system.  It is designed to
   facilitate the transport of DNS messages opaquely, across problematic
   sections of the Internet.  It uses JSON encoding, and HTTP(S) as the
   protocol for transport.

   The main criteria of SPARTACUS is that it preserve DNS messages
   verbatim, and that only properly formatted DNS messages are passed.

   There are two modes (so far) defined: DNS forwarder (dns clients
   point to a local gateway, which forwards to a remote gateway for
   sending to a DNS resolver); and transparent proxy (DNS packets are
   intercepted, passed to a local gateway, which sends them to the
   remote gateway, with original destination IP address etc. encoded,
   and used by the remote gateway as the destination).

   DNS messages are NAT-friendly, so changes to IP or UDP headers do not
   impact them.  Thus, SPARTACUS does not interfere with TSIG, SIG(0),
   or Eastlake Cookies.

   This document describes the system, the components, and behavior,
   with examples.

Author's Note

   Intended Status: Proposed Standard.

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 http://datatracker.ietf.org/drafts/current/.





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   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 April 18, 2015.

Copyright Notice

   Copyright (c) 2014 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
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
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   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  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Problem Statement . . . . . . . . . . . . . . . . . . . .   3
     1.2.  Rationale . . . . . . . . . . . . . . . . . . . . . . . .   4
     1.3.  Related Work  . . . . . . . . . . . . . . . . . . . . . .   5
       1.3.1.  Comparison  . . . . . . . . . . . . . . . . . . . . .   5
   2.  Requirements  . . . . . . . . . . . . . . . . . . . . . . . .   6
   3.  System Overview . . . . . . . . . . . . . . . . . . . . . . .   6
     3.1.  System Elements . . . . . . . . . . . . . . . . . . . . .   7
       3.1.1.  Node Types  . . . . . . . . . . . . . . . . . . . . .   7
     3.2.  System Modes  . . . . . . . . . . . . . . . . . . . . . .   7
       3.2.1.  Details on DNS Forwarder mode . . . . . . . . . . . .   8
       3.2.2.  Details on Transparent Proxy mode . . . . . . . . . .   9
     3.3.  Interoperability  . . . . . . . . . . . . . . . . . . . .  11
       3.3.1.  In-scope and out-of-scope . . . . . . . . . . . . . .  11
   4.  Interactions and Behavior . . . . . . . . . . . . . . . . . .  12
     4.1.  DNS Gateway Encodings . . . . . . . . . . . . . . . . . .  13
     4.2.  UDP Packet Loss . . . . . . . . . . . . . . . . . . . . .  13
     4.3.  Malformed UDP response  . . . . . . . . . . . . . . . . .  13
     4.4.  DNSSEC Validation Failure . . . . . . . . . . . . . . . .  14
   5.  Client-Server Selection and Topology Examples . . . . . . . .  14
     5.1.  Mixed Traffic Walk-Through  . . . . . . . . . . . . . . .  16
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  16
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  16
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  17



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   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  17
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  17
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  18
   Appendix A.  DNS Message Encoding Examples  . . . . . . . . . . .  18
     A.1.  Simple Query/Answer, No EDNS or DNS Server  . . . . . . .  19
     A.2.  Simple Query/Answer, EDNS, no DNS Server  . . . . . . . .  21
     A.3.  Simple Query/Answer, no EDNS, with DNS Server . . . . . .  24
     A.4.  Simple Query/Answer, with EDNS and DNS Server . . . . . .  28
   Appendix B.  Server Gateway HTML code . . . . . . . . . . . . . .  32
   Appendix C.  Server Gateway HTTP POST Handler Pseudo-code . . . .  32
   Appendix D.  Client Gateway Pseudo-code . . . . . . . . . . . . .  33
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  34

1.  Introduction

   DNS (The Domain Name System) has been deployed since the 1980's
   [RFC1033][RFC1034][RFC1035].  Since that time, some of the original
   Resource Record types have been made officially obsolete [RFC3425].
   Some elements have been clarified [RFC2181][RFC2308].  New Resource
   Records have been added [RFC2136][RFC2845][RFC2930][RFC6891].  New
   definitions of bits in the header have arisen, in part due to
   DNSSEC's AD and CD bits [RFC4033][RFC4034][RFC4035][RFC5155].

   This has resulted in now-outdated implementations of stateful devices
   (e.g. devices doing either NAT or packet inspection) interfering with
   end-to-end communication between DNS speakers.  Old devices or
   implementations reject DNS packets that include these newer
   capabilities, features, or format changes.

   At the same time, there has arisen a variety of other devices and
   systems whose deliberate function is to block, capture, or modify DNS
   traffic, for profit or for ideological reasons.  Examples include
   hotel wifi systems, ISPs, and state actors.

   Owing to the stateless nature of DNS over UDP, it is not possible to
   distinguish between deliberate and accidental sources of DNS
   interference.

1.1.  Problem Statement

   There is a need to provide ways of supporting incremental deployment
   of new DNS features, in such a way as to prevent deliberate and/or
   accidental interference in the communication between DNS speakers.

   For example, DNS speakers could communicate over protected channels
   and with data integrity validation via DNSSEC.  The foremost
   limitation is that the communication be over any other port/protocol
   combination than UDP port 53.  Ideally, the choice should be an



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   encoding that is compatible with whatever port/protocol combination
   is selected (versus overloading the port/protocol with incompatible
   payloads).

   There is a further need for the communications channel(s) to be
   standardized, and to not introduce further interoperability problems
   at the DNS protocol level.  Independent implementations need to
   interoperate completely, to avoid merely pushing the compatibility
   problem around.

   In order to solve these problems (individually and/or collectively),
   the SPARTACUS system has been developed.

1.2.  Rationale

   SPARTACUS (Secure, Private Aparatus for Resolution Transported Across
   Constraining and/or Unmaintained Systems), is a system for encoding
   and decoding DNS messages (the DNS payload of UDP or TCP packet
   streams).

   The SPARTACUS system consists of bidirectional DNS gateways for
   transporting DNS over HTTP(S) using a JSON encoding scheme.  This is
   intended to create "bridges" between DNS speakers; perhaps a better
   analogy would be "ferries", as there is no requirement for a tightly
   bound relationship between individual Client nodes and Server nodes.

   Standardizing the JSON encoding used by SPARTACUS, is intended to
   ensure a greater likelihood of compatible, interoprable
   implementations.

   The goal is to transport DNS messages from any Client implementation
   to any Server implementation.

   Each gateway must be liberal in what it accepts (any valid DNS
   message conforming to the relevant RFCs, regardless of DNS
   implementation) and conservative in what it sends (all packets must
   parse correctly as DNS messages).  In order to ensure forward
   compatibility, unknown Types and (in the case of OPT) sub-types, MUST
   be accepted and transported.

   DNS messages MUST traverse the encode/decode process unaltered.  The
   round-trip is designed to, and MUST be implemented to, preserve the
   entire DNS message's fidelity.  This means a 1:1 binary match between
   input, encoding, decoding, and output.  The lengths MUST match, and
   messages MUST be identical, bit for bit.

   A secondary objective of the encoding in JSON is the use of the same
   names for data elements and structures as in the DNS RFCs.  The idea



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   is to provide human-readable JSON encodings, for easier diagnostics
   during development, and when investigating operational issues.

1.3.  Related Work

   A variety of other work exists, and provided inspiration for the
   SPARTACUS work.  This includes web/JSON DNS portals, for providing
   DNS query responses in JSON format, often with a "looking glass"
   functionality.  FIXME format this list appropriately and decorate
   with words.  END FIXME

   o  Multi-location DNS Looking Glass - Tool for performing DNS queries
      via RESTful interface in multiple locations, returning results in
      JSON format

   o  DNS Looking Glass - Tool for performing DNS queries via RESTful
      interface, returning results in JSON format

   o  DNS JSON - Source code project from circa 2009, partially
      developed but incomplete/abandoned

   o  DNSSEC-trigger[trigger] - embedded control function in NLnetlabs'
      Unbound resolver, for attempting DNS queries over TCP port 80 when
      DNSSEC problems are encountered

   o  Various other web-based DNS lookup tools

1.3.1.  Comparison

   There has been at least one previous effort to develop code for a
   DNS-JSON encoding, which appears to have been abandoned after one-way
   encoding was done, circa 2009.  The project focused on presenting
   results to DNS queries in JSON format, with an intention to create a
   client gateway, which never materialized.  The project can be found
   in two places ([JPF_jsondns] and [jsondns.org]).  One major
   difference is that DNS query response status is converted to HTTP
   error codes, rather than being embedded in the JSON answer.  This
   makes it unsuitable for bidirectional use.  Only a few DNS type codes
   were implemented.

   Another DNS JSON tool [fileformat.info], similarly focuses only on
   answers, with a limited number of type codes.

   Yet another tool for looking up DNS via HTTP with JSON responses is
   the "dnsrest" [restdns.net].  It too focuses only on answer values,
   and is similarly not able to fully produce results that can be turned
   back into DNS answer packets.




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   The "DNS Looking Glass" [bortzmeyer.org], is primarily designed for
   returning DNS answer data.  As such, it lacks encoding suitable for a
   bidirectional scheme.  It is primarily focused on XML output, with
   JSON output organized around DNS resolution meta-data, plus answer
   data in a generic schema.  (The schema itself is described in
   [draft-bortzmeyer-dns-json].)

   The "Multilocation DNS Looking Glass" [dns-lg.com], uses a RESTful
   query mechanism of "node/qname/qtypename" to request the looking
   glass (LG) to perform a DNS lookup for the qname and qtype, and
   returns the response in a JSON format.  The JSON format is generic,
   encapsulating all types as string data in presentation format, with a
   generic label of "rdata".  This does not facilitate decoding easily,
   as the JSON scheme provides no information for parsing the rdata
   field.  The type (qtype for the query, or type for answer/authority/
   additional) is in string (symbolic) form, and the elements are
   objects and thus in unordered lists.  The JSON scheme is fine for
   one-way encoding for human readability, but not suitable for two-way
   conversion back into DNS.

   DNSSEC-trigger[trigger] can only be used in environments that use
   NLnetlabs' Unbound resolver, or where Unbound can be deployed as a
   replacement for existing recursive resolvers and/or stub resolvers.

   A variety of other web lookup tools exist, predominantly producing
   DNS validation (zone structure and hierarchy), maps, meta-data, or
   literal output from the 'dig' tool, in formats as varied as the
   purposes of the tools.  Dig output, while being reasonably
   deterministic, is not sufficiently well-formed as to facilitate
   "screen scraping" as a parsing method.

2.  Requirements

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

3.  System Overview

   The SPARTACUS system is designed to improve the reliability and
   security of the DNS system, by providing the means to transport DNS
   traffic across segments of the Internet.  The goal is to bypass
   problem areas which interfere with DNS communications, regardless of
   root cause of the interference.

   Some familiarity with the DNS protocol is assumed.





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3.1.  System Elements

   The particular system elements used will differ, based on the mode of
   operation of the Client.  Clients may request the use of particular
   resolvers via additional intra-element signalling.

3.1.1.  Node Types

   Base node types are the following:

   o  Standalone SPARTACUS Client forwarder

   o  Transparent SPARTACUS proxy Client

   o  Standalone SPARTACUS Server

   o  Apache module-based SPARTACUS Server

   o  Stub resolver

   o  External recursive resolver

   o  Client-side recursive resolver

   o  External authority server

   Future node types are expected to include:

   o  Browser-integrated SPARTACUS client and stub resolver

   o  Mobile-device SPARTACUS client and stub resolver (with exposed
      getdns API)

   o  SMTP-integrated SPARTACUS client and stub resolver

3.2.  System Modes

   The system has two modes of operation:

   o  DNS Forwarder - an opaque mode of operation, the Client/Server
      pair act collectively as a single DNS forwarder.

   o  Transparent Proxy - In this mode, regular DNS traffic is diverted
      by unspecified means to the SPARTACUS Client.

   Additional intra-element signalling facilitates Clients requesting
   particular resolvers' (recursive or authoritative) use.




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3.2.1.  Details on DNS Forwarder mode

   The Server is configured to use a particular DNS recursive resolver,
   with the optional ability to support Client-requested resolver(s) via
   in-band signaling.  If present, the Client-requested resolver IP
   address is passed as an EDNS OPT value.  The Server, if it is
   configured to honor requested resolvers, uses this IP address instead
   of the default.


   Example: Problem caused by firewalls that do not support DNSSEC:

   +------+    +--------------+            +----------+
   |      |    |              |  Blocked   |          |
   | Stub +--> | Old Firewall +----+X+---> | Resolver |
   |      |    | (no DNSSEC)  |  Packets   |          |
   +------+    +--------------+            +----------+

                                 Figure 1

   Example: How the stub client sees the SPARTACUS Client/Server pair,
   in the opaque forwarder configuration:

   +------+    +----------------------------------+      +----------+
   |      |    |                                  |      |          |
   | Stub +--> |            Forwarder             +----> | Resolver |
   |      |    |           with DNSSEC            |      |          |
   |      | <--+                                  | <----+          |
   +------+    +----------------------------------+      +----------+

                                 Figure 2

   Example: How the Client/Server pair actually operates:

   +------+     +--------+               +--------+      +----------+
   |      |     |        |               |        |      |          |
   | Stub +---> | Client +-------------> | Server +----> | Resolver |
   |      | DNS |        | JSON/HTTP(S)  |        | DNS  |          |
   |      | <---+        | <-------------+        | <----+          |
   +------+     +--------+               +--------+      +----------+

                                 Figure 3









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   Example: How the Client/Server bypass the old firewall:

   +------+   +--------+  +--------------+  +--------+   +----------+
   |      |   |        |  | Old Firewall |  |        |   |          |
   | Stub +-> | Client +------------------> | Server +-> | Resolver |
   |      |   |        |  |  (bypassed)  |  |        |   |          |
   |      | <-+        | <------------------+        | <-+          |
   +------+   +--------+  +--------------+  +--------+   +----------+

                                 Figure 4

3.2.2.  Details on Transparent Proxy mode

   Transparent Proxy mode supports transport of stub to recursive
   traffic (all with the same destination IP address).

   Transparent Proxy mode also supports use by a recursive resolver, to
   handle recursive-to-authoritative traffic (with different destination
   IP addresses per query).

   From the perspective of the DNS client (stub or recursive), it
   appears that the DNS query packet went to some IP address, and the
   reply came back directly.

   +----------+                                      +--------------+
   |          +------------------------------------> |              |
   |   Stub   |                                      |   Recursive  |
   |  src=SR  | DNS UDP/53 SR<->RR                   |    dst=RR    |
   |          |                                      |              |
   |          | <------------------------------------+              |
   +----------+                                      +--------------+

                                 Figure 5


















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   +-----------+
   |           +-----------------------------------> +--------------+
   |           |                                     | Authority #1 |
   |           | <-----------------------------------+   dst=AR_1   |
   |           |                                     +--------------+
   |           +-----------------------------------> +--------------+
   | Recursive |                                     | Authority #2 |
   |  src=RR   | <-----------------------------------+   dst=AR_2   |
   |           |                                     +--------------+
   |           |                                          ...
   |           +-----------------------------------> +--------------+
   |           |                                     | Authority #N |
   |           | <-----------------------------------+   dst=AR_N   |
   +-----------+                                     +--------------+
                   DNS UDP/53 RR<->AR_N (N=1,2,...)

                                 Figure 6

   In both use cases, the original IP destination is encoded as an EDNS
   OPT value, and the DNS message (encoded as JSON) is sent to the
   SPARTACUS Server.  The Server sends the DNS message to the original
   IP destination, with the SPARTACUS Server's IP address as the source.
   The resulting answer DNS message is sent to the Client, which changes
   the reply source IP address to the original destination IP address.

   +-----------+            +-------+  +---------+   +---------------+
   |           |            |       |  |         |   |               |
   |           +----------> | Trans.|  | Server  +-> | Authoritative |
   |           |            | Proxy |  | Gateway |   |  Resolver #1  |
   |           | <----------+  TP   |  |   SG    | <-+     AR_1      |
   |           |            +-----+-+  +------+--+   +---------------+
   |           | DNS UDP/53       |           |         DNS UDP/53
   | Recursive | RR <-> AR_1    ^ v        ^  |         SG <-> AR_1
   | Resolver  |                |          |  |
   |    RR     |            +---+-----+    |  |
   |           |            | Client  +----+  |   TCP/80 (or /443)
   |           |            | Gateway |       | JSON (EDNS: dst=AR_1)
   |           |            |   CG    | <-----+      CG <-> SG
   +-----------+            +---------+

                                 Figure 7

   The only practical difference is that some intermediate devices see
   JSON/HTTP(S) instead of DNS/UDP traffic.  For some of those devices,
   this is in fact the purpose of SPARTACUS - preventing those devices
   from inspecting the DNS traffic in a problematic manner.





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3.3.  Interoperability

   The purpose of this document is to ensure that independent
   implementations of Client(s) and Server(s) can interoperate, so long
   as each is permitted to interoprate with the other.

   It is not required that Servers be operated in a completely "open"
   manner.  However, the more open Servers there are, the greater the
   benefit.  Like any web-based service, care should be given towards
   managing available resources on a Server.  In all likelihood, this
   resource management may be most effectively handled via the web
   server's own service management system.

3.3.1.  In-scope and out-of-scope

   The following items are out-of-scope, from an interoperability
   standpoint.

   This means that individual implementations may make independent
   design decisions, without impacting interoperability.

   o  Choice(s) of default resolver (on Server)

   o  Server-side DNS retry and time-out values

   o  How Client(s) select Servers

   The following items are in-scope, from an interoperability
   standpoint.

   o  JSON encoding

   o  How to signal non-support of requested resolver(s)

   o  How to signal "no response" (timeout) on Server-resolver traffic

   o  Signalling/encoding of default,requested, and actually-used
      resolvers

   o  Stripping of EDNS OPT private values

   o  Stripping of synthesized EDNS OPT record

   The following items are optional, from an interoperability
   standpoint.

   o  Whether and how to do edns-client-subnet (on Client)




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   o  Whether to use TLS (HTTPS) on Client-Server traffic

   o  Whether to honor requested resolvers (on Server)

   o  Whether to support Transparent Proxy mode (on the Client)

   o  Whether to do DNSSEC validation

   o  Whether to do PKI validation of SSL certificates (if HTTPS is used
      and CA-issued certs used)

   o  Whether to do DANE validation of SSL certificates (if HTTPS is
      used and TLSA records exist)

   o  Whether IPv4 or IPv6 is supported

4.  Interactions and Behavior

   The Client Gateway needs to make informed decisions about Server
   Gateways to use.  Client Gateways may use pre-configured (static)
   gateways, or may employ any number of strategies for selection of
   Server Gateways.

   In order to enble Client-controlled Server Selection, each Server
   Gateway needs to advise the Client about default and actual DNS
   Servers used.  The Client optionally requests DNS Server(s) that the
   Server should use.  If present, the Server includes that in the
   response.

   The SPARTACUS client/server interaction occurs over TCP rather than
   UDP.  As such, other than TCP-based failures (RST aka "reset" for
   example), every query MUST get a response (owing to the HTTP POST
   standards).

   Since the Server Gateway is performing DNS resolution using UDP
   transport, it is possible that network packet loss may occur,
   resulting in unanswered queries.

   Also, there are reasons other than network-based packet loss that can
   result in unanswered queries.  DNS resolvers must attempt to infer
   what causes queries to not be answered.

   It is also possible that various other failure modes could occur,
   which need to be handled on the basis of the nature of the failure.

   Each of these is addressed in separate sections below.





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4.1.  DNS Gateway Encodings

   The three DNS Server values (default, requested, actual) are
   communicated via EDNS OPT type-length-value (TLV) tuples, using three
   distinct types.  Pre-standard experimental values are presently being
   used.  IANA will need to assign permanent OPT Type values for these
   three type codes.

   In order to ensure that the EDNS OPT record is only returned to the
   original DNS client if it existing in the query, it is necessary to
   identify cases where the DNS Server value encoding resulted in a
   "new" OPT record, rather than being added to an existing record.  In
   such cases, an additional OPT TLV type is required, and is added to
   the OPT record.  A fourth OPT Type value needs to be assigned by IANA
   for this purpose.

   The new OPT codes are used to enable the Client and Server to
   maintain all communication details inside the DNS message itself.
   This simplifies the design, implementation, and operation of Clients
   and Servers, and ensures forward/backward compatibility.  OPT codes
   specific to the Client-Server communication MUST be removed prior to
   forwarding of DNS messages to DNS Clients and Servers.  If the EDNS
   OPT RR is synthesized (added to the DNS message), it MUST be removed.

4.2.  UDP Packet Loss

   In cases where the Server Gateway did not get a response from the DNS
   Server, it needs to signal this back to the client.  It needs to do
   this so that the proper Client state is established.  This prevents
   time-out based (undefined) behavior on the Client from being
   triggered.  The Server needs to "pass along" packet loss status to
   the Client to trigger well-defined Client behavior.

   The mechanism is to use a Private EDNS OPT type/length/value (TLV),
   with the original Question echoed back (to associate with the Query).
   When receiving this TLV, the Client will treat this as a lost UDP
   packet, and MUST NOT send back any UDP packet.  The UDP client is
   responsible for handling this lost UDP packet, per the DNS protocol.

4.3.  Malformed UDP response

   The malformed UDP packet may not be legitimate.  To be conservative,
   this condition is signaled back to the client, and the (actual)
   received UDP packet is rejected/dropped.  This is treated by the DNS
   client as a lost UDP packet.






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4.4.  DNSSEC Validation Failure

   If DNSSEC validation fails, the presumption needs to be made that the
   failure is deliberate.  The DNSSEC standards call for "SRVFAIL"
   responses, so that is what a compliant implementation MUST return to
   the UDP client.

   If the Client and/or Server does DNSSEC Validation, it MUST correctly
   implement Validation signalling via the AD and CD bits.

   In other words, it MUST return the answer regardless of Validation if
   the CD bit is set, and it MUST set the AD bit if Validation succeeds,
   regardless of the presence and/or state of EDNS bit DO.

5.  Client-Server Selection and Topology Examples

                       +-----------+
                       |           |
                  +--> | Server    +--+
   +-----------+  |    | Gateway 1 |  |
   |  Client   |  |    +-----------+  |    +-----------+
   |  Gateway  +--+    +-----------+  +--> |           |
   |           |       |           |       | Recursive |
   |  Selects  +-----> | Server    +-----> |    DNS    |
   |  Random   |       | Gateway 2 |       |   Server  |
   |  Server   +--+    +-----------+  +--> |           |
   |  Gateway  |  |    +-----------+  |    +-----------+
   +-----------+  |    |           |  |
                  +--> | Server    +--+
                       | Gateway 3 |
                       +-----------+

                                 Figure 8

   Figure 8 shows the same Recursive DNS Server being used, via multiple
   Server Gateways.  There are several benefits to doing this; they
   include distributing load among multiple Server Gateways, and
   reducing the amount of DNS traffic going via any single Server
   Gateway.  This limits the impact of the compromise of any single
   Server Gateway, or of any single Server Certificate compromise.











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                              +--------+
                              |        |
                      +-----> | Server |
   +-----------+      |       | GW 1   |                 +-----------+
   |  Client   |  +---+----+  +------+-+   +--------+    |           |
   |  Gateway  |  |        |         |     |        |    |           |
   |           |  | Server | <--+    +---> | Server +--> |           |
   |  Selects  |  | GW 2   |    |          | GW 4   |    |    DNS    |
   |  Random   |  +--------+  +-+------+   +--------+    |   Server  |
   |  Server   |              |        |                 |           |
   |  Gateway  |              | Server |                 |           |
   |           +------------> | GW 3   |                 |           |
   +-----------+              +--------+                 +-----------+

                                 Figure 9

   Figure 9 illustrates a path where more than one Server Gateway is
   traversed during resolution.  The objective here is to disassociate
   the IDENTITY of the client from the CONTENT of the query/answer.  The
   association is only made directly on the first Server Gateway (and
   only with respect to the Client Gateway).  The actual association of
   the source UDP client is only done on the Client Gateway itself,
   which may or may not provide further privacy.  Since there is more
   than one Server-Server hop, this significantly reduces the ability to
   infer associations between Query/Response and Client Gateways.

   It should be noted that this looks very much like TOR (The Onion
   Router), applied to JSON-encoded UDP DNS traffic.  There is a
   proposal for DNS privacy enhancements that applies a similar
   techique, directly on UDP-based DNS queries/answers.  FIXME add xref
   here to reference to the appropriate Internet Draft.  END FIXME

   +---------------+ +--------+ +--------+ +------------+   +----------+
   |    Client     | | WWW/GW | | WWW/GW | |            |   |          |
   |    Gateway    | | Server | | Server | | Web Server |   |          |
   |               | | GW 3   | | GW 4   | |            |   |          |
   |    Selects    | +--------+ +--------+ +----------+ |   |   DNS    |
   |     Among     |                       | Gateway  | |   |  Server  |
   |  Most Recent  |  DNS traffic mingled  | Server   | |   |          |
   |   Web Server  |   with web traffic    | Module   +---> |          |
   |    Gateways   +---------------------> |  GW 2    | |   |          |
   +---------------+    (or encrypted)     +----------+-+   +----------+

                                 Figure 10

   Figure 10 illustrates one query/response when the client is
   attempting to use something similar to steganography to preserve
   privacy.  In this context, the privacy against passive monitoring is



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   achieved by using un-blocked web servers which are also Server
   Gateways.  A MitM adversary cannot easily block this traffic without
   blocking the entire site, or by inspecting every flow to/from the
   site.  A passive observer would similarly need to inspect all flows
   to find the embedded, encoded DNS traffic.  The DNS traffic would be
   nearly indistinguishable from regular HTTP traffic.

   Note that the use of TLS to protect the Client-Server traffic would
   make it impossible to distinguish the DNS traffic from the other web
   trafficin this situation.  Combining this "tag-along" with TLS
   provides both strong privacy and strong security.

5.1.  Mixed Traffic Walk-Through

   Suppose a client were to visit web sites "a" through "j"
   sequentially, i.e. a,b,c,d,e,f,g,h,i,j.  Suppose some of those were
   also Server Gateways, represented by upper case (vs lower case for
   web sites without Server Gateway capabilities).  Thus the sequence
   would be A,b,C,D,e,f,g,H,I,j.  If the Client Gateway chose a Server
   Gateway randomly from among the last four web sites visited, the
   sequence of events after visiting A through D, would look like:

   o  Select Server from set {A,C,D}, look up "e".  Visit "e".

   o  Select Server from set {C,D}, look up "f".  Visit "f".

   o  Select Server from set {C,D}, look up "g".  Visit "g".

   o  Select Server from set {D}, look up "h".  Visit "h".

   o  Select Server from set {D,H}, look up "i".  Visit "i".

   o  Select Server from set {H,I}, look up "j".  Visit "j".

   An observer close to the Client would see traffic within a given time
   window, only to the same set of Web servers.  An observer close to
   any of the Web servers would only see traffic from a given client,
   for a small interval of time after the first visit.

6.  Security Considerations

   (None per se.)  Need to list considerations etc.

7.  IANA Considerations

   This document will eventually contain IANA-specific material.





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8.  Acknowledgements

   To be added later.

9.  References

9.1.  Normative References

   [RFC1033]  Lottor, M., "Domain administrators operations guide", RFC
              1033, November 1987.

   [RFC1034]  Mockapetris, P., "Domain names - concepts and facilities",
              STD 13, RFC 1034, November 1987.

   [RFC1035]  Mockapetris, P., "Domain names - implementation and
              specification", STD 13, RFC 1035, November 1987.

   [RFC2136]  Vixie, P., Thomson, S., Rekhter, Y., and J. Bound,
              "Dynamic Updates in the Domain Name System (DNS UPDATE)",
              RFC 2136, April 1997.

   [RFC2181]  Elz, R. and R. Bush, "Clarifications to the DNS
              Specification", RFC 2181, July 1997.

   [RFC2308]  Andrews, M., "Negative Caching of DNS Queries (DNS
              NCACHE)", RFC 2308, March 1998.

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

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

   [RFC3425]  Lawrence, D., "Obsoleting IQUERY", RFC 3425, November
              2002.

   [RFC4033]  Arends, R., Austein, R., Larson, M., Massey, D., and S.
              Rose, "DNS Security Introduction and Requirements", RFC
              4033, March 2005.

   [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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   [RFC5155]  Laurie, B., Sisson, G., Arends, R., and D. Blacka, "DNS
              Security (DNSSEC) Hashed Authenticated Denial of
              Existence", RFC 5155, March 2008.

   [RFC6891]  Damas, J., Graff, M., and P. Vixie, "Extension Mechanisms
              for DNS (EDNS(0))", STD 75, RFC 6891, April 2013.

9.2.  Informative References

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

   [JPF_jsondns]
              "DNS over HTTP", <http://github.com/jpf/jsondns>.

   [jsondns.org]
              Franusic, J., "Query DNS via REST", <http://jsondns.org/>.

   [fileformat.info]
              Marcuse, A., "DNS in client-side JavaScript",
              <http://www.fileformat.info/tool/rest/dns-json.htm>.

   [restdns.net]
              "REST-DNS", <http://restdns.net/>.

   [bortzmeyer.org]
              Bortzmeyer, S., "DNS Looking Glass",
              <http://www.bortzmeyer.org/dns-lg.html>.

   [draft-bortzmeyer-dns-json]
              Bortzmeyer, S., "DNS in JSON",
              <http://tools.ietf.org/html/draft-bortzmeyer-dns-json-01>.

   [dns-lg.com]
              Cambus, F., "Multilocation DNS Looking Glass",
              <http://www.dns-lg.com/>.

   [trigger]  NLnet Labs, "Dnssec-Trigger",
              <http://www.nlnetlabs.nl/projects/dnssec-trigger/>.

Appendix A.  DNS Message Encoding Examples

   The entire encoding of pairs of DNS messages follows.  For each
   pair,the first is the query, and the second is the response.







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A.1.  Simple Query/Answer, No EDNS or DNS Server

   Query encoded in JSON:

   "PACKET (RFC 1035)" : [
   "ROLE" : "client",
   "DSIZE" : 26,
   "DICTIONARY" : [
   "example",
   "com",
   ""
   ],
   "DSIZE2" : 26,
   "Header" : [
   "ID" : 42,
   "HFlags" : [
   "QR" : false,
   "Opcode" : [ "Query" : 0 ],
   "AA" : false,
   "TC" : false,
   "RD" : true,
   "RA" : false,
   "Z" : false,
   "AD" : false,
   "CD" : false,
   "RCODE" : [ "NoError (RFC 1035)" : 0 ]

   ],
   "QDCOUNT" : 1,
   "ANCOUNT" : 0,
   "NSCOUNT" : 0,
   "ARCOUNT" : 0
   ],
   "Question" : [
   "QUESTION (RFC 1035)" : [
   "QNAME" : [ "example.com." : 0 ],
   "QTYPE" : [ "A" : 1 ],
   "QCLASS" : [ "IN" : 1 ]
   ]
   ]
   ]

   Response encoded in JSON:

   "PACKET (RFC 1035)" : [
   "ROLE" : "client",
   "DSIZE" : 33,
   "DICTIONARY" : [



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   "example",
   "com",
   "",
   "@0"
   ],
   "DSIZE2" : 33,
   "Header" : [
   "ID" : 42,
   "HFlags" : [
   "QR" : true,
   "Opcode" : [ "Query" : 0 ],
   "AA" : false,
   "TC" : false,
   "RD" : true,
   "RA" : true,
   "Z" : false,
   "AD" : false,
   "CD" : false,
   "RCODE" : [ "NoError (RFC 1035)" : 0 ]

   ],
   "QDCOUNT" : 1,
   "ANCOUNT" : 1,
   "NSCOUNT" : 0,
   "ARCOUNT" : 0
   ],
   "Question" : [
   "QUESTION (RFC 1035)" : [
   "QNAME" : [ "example.com." : 0 ],
   "QTYPE" : [ "A" : 1 ],
   "QCLASS" : [ "IN" : 1 ]
   ]
   ],
   "Answer" : [
   "RR" : [
   "NAME" : [ "example.com." : 0 ],
   "TYPE" : [ "A" : 1 ],
   "CLASS" : [ "IN" : 1 ],
   "TTL" : 5218,
   "RDLENGTH" : 4,
   "RDATA" : [
   "A" : [
   "Address" : "93.184.216.119"
   ]
   ]
   ]
   ]
   ]



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A.2.  Simple Query/Answer, EDNS, no DNS Server

   Query encoded in JSON:

   "PACKET (RFC 1035)" : [
   "ROLE" : "client",
   "DSIZE" : 31,
   "DICTIONARY" : [
   "example",
   "com",
   "",
   ""
   ],
   "DSIZE2" : 31,
   "Header" : [
   "ID" : 42,
   "HFlags" : [
   "QR" : false,
   "Opcode" : [ "Query" : 0 ],
   "AA" : false,
   "TC" : false,
   "RD" : true,
   "RA" : false,
   "Z" : false,
   "AD" : false,
   "CD" : false,
   "RCODE" : [ "NoError (RFC 1035)" : 0 ]

   ],
   "QDCOUNT" : 1,
   "ANCOUNT" : 0,
   "NSCOUNT" : 0,
   "ARCOUNT" : 1
   ],
   "Question" : [
   "QUESTION (RFC 1035)" : [
   "QNAME" : [ "example.com." : 0 ],
   "QTYPE" : [ "A" : 1 ],
   "QCLASS" : [ "IN" : 1 ]
   ]
   ],
   "Additional" : [
   "RR" : [
   "NAME" : [ "." : 3 ],
   "TYPE" : [ "OPT" : 41 ],
   "Field3" : [
   "UDPSIZEFIELD" : [
   "UDPSIZE" : 1500



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   ]
   ],
   "Field4" : [
   "Extended_RCode_Flags" : [
   "ERCFlagbits" : [
   "RCode" : 0,
   "Version" : 0,
   "DO" : false,
   "Resv" : 0

   ]
   ]
   ],
   "RDLENGTH" : 0,
   "RDATA" : [
   "OPT (RFC 6891)" : [
   "TLV_LIST" : [

   ]
   ]
   ]
   ]
   ]
   ]

   Response encoded in JSON:

   "PACKET (RFC 1035)" : [
   "ROLE" : "client",
   "DSIZE" : 38,
   "DICTIONARY" : [
   "example",
   "com",
   "",
   "@0",
   ""
   ],
   "DSIZE2" : 38,
   "Header" : [
   "ID" : 42,
   "HFlags" : [
   "QR" : true,
   "Opcode" : [ "Query" : 0 ],
   "AA" : false,
   "TC" : false,
   "RD" : true,
   "RA" : true,
   "Z" : false,



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   "AD" : false,
   "CD" : false,
   "RCODE" : [ "NoError (RFC 1035)" : 0 ]

   ],
   "QDCOUNT" : 1,
   "ANCOUNT" : 1,
   "NSCOUNT" : 0,
   "ARCOUNT" : 1
   ],
   "Question" : [
   "QUESTION (RFC 1035)" : [
   "QNAME" : [ "example.com." : 0 ],
   "QTYPE" : [ "A" : 1 ],
   "QCLASS" : [ "IN" : 1 ]
   ]
   ],
   "Answer" : [
   "RR" : [
   "NAME" : [ "example.com." : 0 ],
   "TYPE" : [ "A" : 1 ],
   "CLASS" : [ "IN" : 1 ],
   "TTL" : 4865,
   "RDLENGTH" : 4,
   "RDATA" : [
   "A" : [
   "Address" : "93.184.216.119"
   ]
   ]
   ]
   ],
   "Additional" : [
   "RR" : [
   "NAME" : [ "." : 4 ],
   "TYPE" : [ "OPT" : 41 ],
   "Field3" : [
   "UDPSIZEFIELD" : [
   "UDPSIZE" : 4000
   ]
   ],
   "Field4" : [
   "Extended_RCode_Flags" : [
   "ERCFlagbits" : [
   "RCode" : 0,
   "Version" : 0,
   "DO" : false,
   "Resv" : 0




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   ]
   ]
   ],
   "RDLENGTH" : 0,
   "RDATA" : [
   "OPT (RFC 6891)" : [
   "TLV_LIST" : [

   ]
   ]
   ]
   ]
   ]
   ]

A.3.  Simple Query/Answer, no EDNS, with DNS Server

   Query encoded in JSON:

   "PACKET (RFC 1035)" : [
   "ROLE" : "client",
   "DSIZE" : 31,
   "DICTIONARY" : [
   "example",
   "com",
   "",
   ""
   ],
   "DSIZE2" : 31,
   "Header" : [
   "ID" : 42,
   "HFlags" : [
   "QR" : false,
   "Opcode" : [ "Query" : 0 ],
   "AA" : false,
   "TC" : false,
   "RD" : true,
   "RA" : false,
   "Z" : false,
   "AD" : false,
   "CD" : false,
   "RCODE" : [ "NoError (RFC 1035)" : 0 ]

   ],
   "QDCOUNT" : 1,
   "ANCOUNT" : 0,
   "NSCOUNT" : 0,
   "ARCOUNT" : 1



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   ],
   "Question" : [
   "QUESTION (RFC 1035)" : [
   "QNAME" : [ "example.com." : 0 ],
   "QTYPE" : [ "A" : 1 ],
   "QCLASS" : [ "IN" : 1 ]
   ]
   ],
   "Additional" : [
   "RR" : [
   "NAME" : [ "." : 3 ],
   "TYPE" : [ "OPT" : 41 ],
   "Field3" : [
   "UDPSIZEFIELD" : [
   "UDPSIZE" : 1500
   ]
   ],
   "Field4" : [
   "Extended_RCode_Flags" : [
   "ERCFlagbits" : [
   "RCode" : 0,
   "Version" : 0,
   "DO" : false,
   "Resv" : 0

   ]
   ]
   ],
   "RDLENGTH" : 19,
   "RDATA" : [
   "OPT (RFC 6891)" : [
   "TLV_LIST" : [
   "TLV" : [
   "TYPE" : [ "PrivateType65500" : 65500 ],
   "Len" : 13,
   "Data" : [
   "PrivateType65500" : [
   "GW_NAME" : [ "10:10" , "198.41.1.1" ]

   ]
   ]
   ],
   "TLV" : [
   "TYPE" : [ "PrivateType65510" : 65510 ],
   "Len" : 0,
   "Data" : [
   ]
   ],



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   ]
   ]
   ]
   ]
   ]
   ]

   Response encoded in JSON:

   "PACKET (RFC 1035)" : [
   "ROLE" : "client",
   "DSIZE" : 38,
   "DICTIONARY" : [
   "example",
   "com",
   "",
   "@0",
   ""
   ],
   "DSIZE2" : 38,
   "Header" : [
   "ID" : 42,
   "HFlags" : [
   "QR" : true,
   "Opcode" : [ "Query" : 0 ],
   "AA" : false,
   "TC" : false,
   "RD" : true,
   "RA" : true,
   "Z" : false,
   "AD" : true,
   "CD" : false,
   "RCODE" : [ "NoError (RFC 1035)" : 0 ]

   ],
   "QDCOUNT" : 1,
   "ANCOUNT" : 1,
   "NSCOUNT" : 0,
   "ARCOUNT" : 1
   ],
   "Question" : [
   "QUESTION (RFC 1035)" : [
   "QNAME" : [ "example.com." : 0 ],
   "QTYPE" : [ "A" : 1 ],
   "QCLASS" : [ "IN" : 1 ]
   ]
   ],
   "Answer" : [



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   "RR" : [
   "NAME" : [ "example.com." : 0 ],
   "TYPE" : [ "A" : 1 ],
   "CLASS" : [ "IN" : 1 ],
   "TTL" : 4084,
   "RDLENGTH" : 4,
   "RDATA" : [
   "A" : [
   "Address" : "93.184.216.119"
   ]
   ]
   ]
   ],
   "Additional" : [
   "RR" : [
   "NAME" : [ "." : 4 ],
   "TYPE" : [ "OPT" : 41 ],
   "Field3" : [
   "UDPSIZEFIELD" : [
   "UDPSIZE" : 512
   ]
   ],
   "Field4" : [
   "Extended_RCode_Flags" : [
   "ERCFlagbits" : [
   "RCode" : 0,
   "Version" : 0,
   "DO" : false,
   "Resv" : 0

   ]
   ]
   ],
   "RDLENGTH" : 19,
   "RDATA" : [
   "OPT (RFC 6891)" : [
   "TLV_LIST" : [
   "TLV" : [
   "TYPE" : [ "PrivateType65500" : 65500 ],
   "Len" : 13,
   "Data" : [
   "PrivateType65500" : [
   "GW_NAME" : [ "10:10" , "198.41.1.1" ]

   ]
   ]
   ],
   "TLV" : [



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   "TYPE" : [ "PrivateType65510" : 65510 ],
   "Len" : 0,
   "Data" : [
   ]
   ],

   ]
   ]
   ]
   ]
   ]
   ]

A.4.  Simple Query/Answer, with EDNS and DNS Server

   Query encoded in JSON:

   "PACKET (RFC 1035)" : [
   "ROLE" : "client",
   "DSIZE" : 31,
   "DICTIONARY" : [
   "example",
   "com",
   "",
   ""
   ],
   "DSIZE2" : 31,
   "Header" : [
   "ID" : 42,
   "HFlags" : [
   "QR" : false,
   "Opcode" : [ "Query" : 0 ],
   "AA" : false,
   "TC" : false,
   "RD" : true,
   "RA" : false,
   "Z" : false,
   "AD" : false,
   "CD" : false,
   "RCODE" : [ "NoError (RFC 1035)" : 0 ]

   ],
   "QDCOUNT" : 1,
   "ANCOUNT" : 0,
   "NSCOUNT" : 0,
   "ARCOUNT" : 1
   ],
   "Question" : [



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   "QUESTION (RFC 1035)" : [
   "QNAME" : [ "example.com." : 0 ],
   "QTYPE" : [ "A" : 1 ],
   "QCLASS" : [ "IN" : 1 ]
   ]
   ],
   "Additional" : [
   "RR" : [
   "NAME" : [ "." : 3 ],
   "TYPE" : [ "OPT" : 41 ],
   "Field3" : [
   "UDPSIZEFIELD" : [
   "UDPSIZE" : 1500
   ]
   ],
   "Field4" : [
   "Extended_RCode_Flags" : [
   "ERCFlagbits" : [
   "RCode" : 0,
   "Version" : 0,
   "DO" : false,
   "Resv" : 0

   ]
   ]
   ],
   "RDLENGTH" : 15,
   "RDATA" : [
   "OPT (RFC 6891)" : [
   "TLV_LIST" : [
   "TLV" : [
   "TYPE" : [ "PrivateType65500" : 65500 ],
   "Len" : 13,
   "Data" : [
   "PrivateType65500" : [
   "GW_NAME" : [ "10:10" , "198.41.1.1" ]

   ]
   ]
   ],

   ]
   ]
   ]
   ]
   ]
   ]




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   Response encoded in JSON:

   "PACKET (RFC 1035)" : [
   "ROLE" : "client",
   "DSIZE" : 38,
   "DICTIONARY" : [
   "example",
   "com",
   "",
   "@0",
   ""
   ],
   "DSIZE2" : 38,
   "Header" : [
   "ID" : 42,
   "HFlags" : [
   "QR" : true,
   "Opcode" : [ "Query" : 0 ],
   "AA" : false,
   "TC" : false,
   "RD" : true,
   "RA" : true,
   "Z" : false,
   "AD" : true,
   "CD" : false,
   "RCODE" : [ "NoError (RFC 1035)" : 0 ]

   ],
   "QDCOUNT" : 1,
   "ANCOUNT" : 1,
   "NSCOUNT" : 0,
   "ARCOUNT" : 1
   ],
   "Question" : [
   "QUESTION (RFC 1035)" : [
   "QNAME" : [ "example.com." : 0 ],
   "QTYPE" : [ "A" : 1 ],
   "QCLASS" : [ "IN" : 1 ]
   ]
   ],
   "Answer" : [
   "RR" : [
   "NAME" : [ "example.com." : 0 ],
   "TYPE" : [ "A" : 1 ],
   "CLASS" : [ "IN" : 1 ],
   "TTL" : 4084,
   "RDLENGTH" : 4,
   "RDATA" : [



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   "A" : [
   "Address" : "93.184.216.119"
   ]
   ]
   ]
   ],
   "Additional" : [
   "RR" : [
   "NAME" : [ "." : 4 ],
   "TYPE" : [ "OPT" : 41 ],
   "Field3" : [
   "UDPSIZEFIELD" : [
   "UDPSIZE" : 512
   ]
   ],
   "Field4" : [
   "Extended_RCode_Flags" : [
   "ERCFlagbits" : [
   "RCode" : 0,
   "Version" : 0,
   "DO" : false,
   "Resv" : 0

   ]
   ]
   ],
   "RDLENGTH" : 15,
   "RDATA" : [
   "OPT (RFC 6891)" : [
   "TLV_LIST" : [
   "TLV" : [
   "TYPE" : [ "PrivateType65500" : 65500 ],
   "Len" : 13,
   "Data" : [
   "PrivateType65500" : [
   "GW_NAME" : [ "10:10" , "198.41.1.1" ]

   ]
   ]
   ],

   ]
   ]
   ]
   ]
   ]
   ]




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Appendix B.  Server Gateway HTML code

   The entire HTML document needed on the Server for the Client to send/
   receive JSON-encoded DNS messages follows:

       <html>
       <body>
       <form action="cgi-bin/json-resolver2.pl" method="POST">
       <P>
       <TEXTAREA name="query" rows="20" cols="80">
       </TEXTAREA>
       <INPUT type="submit" value="Send"><INPUT type="reset">
       </P>
       </form>
       </body>
       </html>

   The "action" target needs to exist and be executable, and ideally be
   performance-optimized (e.g. via use of mod_perl).

Appendix C.  Server Gateway HTTP POST Handler Pseudo-code

   The following pseudo-code illustrates the high-level behavior of the
   HTML handler for the Server.

   The handler is passed the contents of the TEXTAREA, which will be the
   JSON-encoded DNS message.
























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   // initialize parser etc.
   // set up socket for UDP query/response to default Resolver
   // set up socket for UDP query/response to client-supplied Resolver
   // extract JSON-encoded DNS message from HTTP POST variable 'query'
   // save original Query-ID, assign new Query-ID (to avoid collisions)
   // decode DNS message (into DNS wire format)
   // if DNS message has OPT Resource Record
   //   if OPT has Client-supplied Resolver option
   //     extract Resolver value
   //     delete Resolver option from OPT
   //   endif
   //   if OPT was synthesized by Client
   //     delete OPT Resource Record
   //   endif
   //   send DNS message to Client-specified Resolver
   // else
   //   send DNS message to default Resolver
   // endif
   // wait for response or timeout
   // if timeout && retry-count < max-retry-count
   //   resend DNS message
   // elsif timeout && retry-count >= max-retry-count
   //   send "retry-count-exceeded" via OPT (synthesized if necessary)
   // else
   //   set DNS answer's Query-ID value to original Query-ID
   //   encode DNS answer
   //   send JSON-encoded answer to Client
   // endif

Appendix D.  Client Gateway Pseudo-code

   The following pseudo-code illustrates the high-level behavior of the
   Client.

   The Client in this example is pre-configured with a single Server
   Gateway's address.















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   // initialize parser etc.
   // set up socket for UDP query/response (Listener)
   // set up HTTP connection to Server Gateway
   // do an HTTP "GET" to the predefined URL of the Server HTML code
   // extract HTML elements needed: handler, variable name
   // loop forever:
   //   listen for DNS query packet
   //   fork (to handle this packet)
   //   if child
   //     save old DNS Query-ID, set new Query-ID
   //     if Use-Supplied-Resolver
   //       if exits OPT
   //         add client-supplied-resolver to OPT
   //       else
   //         synthesize OPT and add client-supplied-resolver
   //       endif
   //     endif
   //     encode DNS message (into JSON)
   //     write HTTP POST onto socket
   //     wait for HTTP response
   //     extract JSON-encoded answer from HTTP
   //     decode DNS answer (from JSON)
   //     if OPT
   //       if OPT.option is error condition
   //         drop answer and continue loop forever:
   //       elsif OPT synthesized
   //         delete OPT
   //       elsif OPT.option SPARTACUS-specific value
   //         delete option
   //       endif
   //     endif
   //     set answer.Query-ID to saved value
   //     send answer to sender
   //   end-of-loop

Author's Address

   Brian Dickson
   12047B 36th Ave NE
   Seattle, wA  98125

   Email: brian.peter.dickson@gmail.com









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