dnsop                                                         P. Wouters
Internet-Draft                                                   Red Hat
Intended status: Standards Track                          April 11, 2014
Expires: October 13, 2014

                      Chain Query requests in DNS


   This document defines an EDNS0 extension that can be used by a DNSSEC
   enabled Recursive Nameserver configured as a forwarder to send a
   single DNS query requesting to receive a complete validation path
   along with the regular DNS answer, without the need to rapid-fire
   many UDP requests in an attempt to attain a low latency.

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/.

   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 October 13, 2014.

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
   carefully, as they describe your rights and restrictions with respect
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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.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Notation . . . . . . . . . . . . . . . . . .   3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Overview  . . . . . . . . . . . . . . . . . . . . . . . . . .   4
   4.  Option Format . . . . . . . . . . . . . . . . . . . . . . . .   5
   5.  Protocol Description  . . . . . . . . . . . . . . . . . . . .   5
     5.1.  Discovery of Support  . . . . . . . . . . . . . . . . . .   5
     5.2.  Generating a Query  . . . . . . . . . . . . . . . . . . .   5
     5.3.  Generating a Response . . . . . . . . . . . . . . . . . .   6
     5.4.  Sending the Option  . . . . . . . . . . . . . . . . . . .   7
   6.  Protocol  Considerations  . . . . . . . . . . . . . . . . . .   7
     6.1.  DNSSEC Considerations . . . . . . . . . . . . . . . . . .   7
     6.2.  NS record Considerations  . . . . . . . . . . . . . . . .   7
     6.3.  TCP Session Management  . . . . . . . . . . . . . . . . .   8
     6.4.  Non-Clean Paths . . . . . . . . . . . . . . . . . . . . .   8
     6.5.  Anycast Considerations  . . . . . . . . . . . . . . . . .   8
   7.  Implementation Status . . . . . . . . . . . . . . . . . . . .   9
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
     8.1.  Amplification Attacks . . . . . . . . . . . . . . . . . .   9
   9.  Examples  . . . . . . . . . . . . . . . . . . . . . . . . . .  10
     9.1.  Simple Query for example.com  . . . . . . . . . . . . . .  10
     9.2.  Out-of-path query for example.com . . . . . . . . . . . .  12
     9.3.  non-existent data . . . . . . . . . . . . . . . . . . . .  12
   10. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  13
     10.1.  EDNS0 option code for edns-chain-query . . . . . . . . .  13
   11. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  14
   12. Normative References  . . . . . . . . . . . . . . . . . . . .  14
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  15

1.  Introduction

   Traditionally, clients operate in stub-mode for DNS.  For each DNS
   question the client needs to resolve, it sends a single query to an
   upstream DNS resolver to obtain a single DNS answer.  When DNSSEC
   [RFC4033] is deployed on such clients, validation requires that the
   client obtains all the (intermediate) information from the DNS root
   down to the queried-for hostname so it can perform DNSSEC validation
   on the complete chain of trust.  This process increases the number of
   DNS queries and answers required, and thus increases the latency
   before a validated DNS answer has been obtained.

   Currently, applications use a rapid-fire approach to send out many
   UDP requests concurrently.  This requires more resources on the DNS
   client with respect to state (cpu, memory, battery) and bandwidth.
   There is also no guarantee that the initial burst of UDP questions
   will result in all the records required for DNSSEC validation, and

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   more round trips could be required depending on the resulting DNS
   answers.  This especially affects high-latency links.

   This document specifies an EDNS0 extension that allows a validating
   recursive name server running as a forwarder to request another
   recursive name server for a DNS chain answer using one DNS query/
   answer pair.  This reduces the number of round-trip times ("RTT") to
   two.  If combined with [TCP-KEEPALIVE] there is only 1 RTT.  While
   the upstream DNS resolver still needs to perform all the individual
   queries required for the complete answer, it usually has a much
   bigger cache and does not experience significant slowdown from last-
   mile latency.

   This EDNS0 extension allows the Forwarder to indicate which part of
   the DNS hierarchy it already contains in its cache.  This reduces the
   amount of data required to be transferred and reduces the work the
   upstream Resolving Nameserver has to perform.

   This EDNS0 extension is only intended for Forwarders.  It can (and
   should be) ignored by Authoritative Nameservers and by Recursive
   Nameservers that do not support this EDNS0 option.

1.1.  Requirements Notation

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

2.  Terminology

   Stub Resolver:  A simple DNS protocol implementation on the client
      side as described in [RFC1034] section 5.3.1.

   Authoritative Nameserver:  A nameserver that has authority over one
      or more DNS zones.  These are normally not contacted by clients
      directly but by Recursive Resolvers.  Described in [RFC1035]
      chapter 6.

   Recursive Resolver:  A nameserver that is responsible for resolving
      domain names for clients by following the domain's delegation
      chain, starting at the root.  Recursive Resolvers frequently use
      caches to be able to respond to client queries quickly.  Described
      in [RFC1035] chapter 7.

   Validating Resolver:  A recursive nameserver that also performs
      DNSSEC [RFC4033] validation.

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   Forwarder:  A Recursive Resolver that is using another (upstream)
      Recursive Resolver instead of querying Authoritative Nameservers
      directly.  It still performs validation.

3.  Overview

   When DNSSEC is deployed on the client, it can no longer delegate all
   DNS work to the upstream Resolving Nameserer.  Obtaining just the DNS
   answer itself is not enough to validate that answer using DNSSEC.
   For DNSSEC validation, the client requires a locally running
   validating DNS server configured as Resolving Nameserver so it can
   confirm DNSSEC validation of all intermediary DNS answers.  It can
   configure itself as a Forwarder if the DHCP server has indicated that
   one or more Resolving Nameservers are available.  Regardless,
   generating the required queries for validation adds a significant
   delay in answering the DNS question of the locally running
   application.  The application has to wait while the Forwarder on the
   client is querying for all the intermediate work.  Each round-trip
   adds to the total time waiting on DNS resolving to complete.  This
   makes DNSSEC resolving impractical on networks with a high latency.

   The edns-chain-query option allows the client to request all
   intermediate DNS data it requires to resolve and validate a
   particular DNS answer in a single round-trip DNS query and answer.

   Servers answering with chain query data exceeding 512 bytes should
   ensure that the transport is TCP or source IP address verified UDP.
   See Section 8.  This avoids abuse in DNS amplification attacks.

   The format of this option is described in Section 4.

   As described in Section 5.3, a recursive nameserver could use this
   EDNS0 option to include additional data required by the client in the
   Authority Section of the DNS answer packet when using a source IP
   verified transport.  The Answer Section remains unchanged from a
   traditional DNS answer and contains the answer and related DNSSEC

   An empty edns-chain-query EDNS0 option MAY be sent over any transport
   as a discovery method.  A DNS server receiving such an empty edns-
   chain-query option SHOULD add an empty edns-chain-query option in its
   answer to indicate that it supports edns-chain-query for source IP
   address verified transports.

   The mechanisms provided by edns-chain-query raise various security
   related concerns, related to the additional work, bandwidth,
   amplification attacks as well as privacy issues with the cache.
   These concerns are described in Section 8.

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4.  Option Format

   This draft uses an EDNS0 ([RFC2671]) option to include client IP
   information in DNS messages.  The option is structured as follows:

                        1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   !         OPTION-CODE           !         OPTION-LENGTH         !
   ~                Last Known Query Name (FQDN)                   ~

   o  (Defined in [RFC2671]) OPTION-CODE, 2 octets, for edns-chain-query
      is [TBD].

   o  (Defined in [RFC2671]) OPTION-LENGTH, 2 octets, contains the
      length of the payload (everything after Option-length) in octets.

   o  Last Known Query Name, a variable length FDQN of the requested
      start point of the chain.  This entry is the 'lowest' known entry
      in the DNS chain known by the recursive server seeking a edns-
      chain-query answer.  The end point of the chain is obtained from
      the DNS Query Section itself.  No compression is allowed for this

   o  Assigned by IANA in IANA-AFI [1].

5.  Protocol Description

5.1.  Discovery of Support

   A Forwarder may include a zero-length edns-chain-query option in
   queries over UDP or TCP to discover the DNS server capability for
   edns-chain-query.  DNS Servers that support and are willing to accept
   chain queries over TCP SHOULD respond to a zero-length edns-chain-
   query received over UDP or TCP queries by including a zero-length
   edns-chain-query option in the answer.  A Forwarder MAY then switch
   to the TCP transport and sent a non-zero edns-chain-query value to
   request a chain-query response from the DNS server.

5.2.  Generating a Query

   The edns-chain-query option should generally be deployed by
   Forwarders, as described in Section 5.4.

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   In this option value, the Forwarder sets the last known entry point
   in the chain - furthest from the root - that it already has a DNSSEC
   validated (secure or not) answer for in its cache.  The upstream
   Recursive Resolver does not need to include any part of the chain
   from the root down to this option's FQDN.  A complete example is
   described in Section 9.

   Depending on the size of the labels of the last known entry point
   value, a DNS Query packet could be arbitrarily large.  If using the
   last known entry point would result in a query size of more then 512
   bytes, the last known entry point should be replaced with its parent
   entry until the query size would be 512 bytes or less.

5.3.  Generating a Response

   When a query containing a non-zero edns-chain-query option is
   received over a TCP connection from a Forwarder, the upstream
   Recursive Resolver supporting edns-chain-query MAY respond by
   confirming that it is returning a DNS Query Chain.  To do so, it MUST
   set the edns-chain-query option with an OPTION-LENGTH of zero to
   indicate the DNS answer contains a Chain Query.  It extends the
   Authority Section for the DNS answer packet with the required DNS
   RRSets resulting in an Authority Section that contains a complete
   chain of DNS RRsets that start with the first chain element below the
   received Last Known Query Name upto and including the NS and DS
   RRsets that represent the zone cut (authoritative servers) of the
   QNAME.  The actual DNS answer to the question in the Query Section is
   placed in the DNS Answer Section identical to traditional DNS
   answers.  If the received query has the DNSSEC OK flag set, all
   required DNSSEC related records must be added to their appropriate
   sections.  This includes records required for proof of non-existence
   of regular and/or wildcard records, such as NSEC or NSEC3 records.

   Recursive Resolvers that have not implemented or enabled support for
   the edns-chain-query option, or are otherwise unwilling to perform
   the additional work for a Chain Query due to work load, may safely
   ignore the option in the incoming queries.  Such a server MUST NOT
   include an edns-chain-query option when sending DNS answer replies
   back, thus indicating it is not able to support Chain Queries at this

   Requests with wrongly formatted options (i.e. bogus FQDN) MUST be
   rejected and a FORMERR response must be returned to the sender, as
   described by [RFC2671], Transport Considerations.

   Requests resulting in chains that the receiving resolver is unwilling
   to serve can be rejected by sending a REFUSED response to the sender,
   as described by [RFC2671], Transport Considerations.  This refusal

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   can be used for chains that would be too big or chains that would
   reveal too much information considered private.

   At any time, a DNS server that has determined that it is running low
   on resources can refuse to acknowledge a Chain Query by omitting the
   edns-chain-query option.  It may do so even if it conveyed support to
   a DNS client previously.  If [TCP-KEEPALIVE] is used, it may even
   change its support for edns-chain-query within the same TCP session.

   If the DNS request results in an CNAME or DNAME for the Answer
   Section, the DNS server MUST return these records in the Answer
   Section similar to regular DNS processing.  The CNAME or DNAME target
   MAY be placed in the Additional Section only if all supporting
   records for DNSSEC validation of the CNAME or DNAME target is also
   added to the Authority Section.

   In any case, the response from the receiving resolver to the client
   resolver MUST NOT contain the edns-chain-query option if none was
   present in the client's resolver original request.

5.4.  Sending the Option

   When edns-chain-query is available, the downstream Resolving
   Nameserver can adjust its query strategy based on the desired queries
   and its cache contents.

   A Forwarder can request the edns-chain-query option with every
   outgoing DNS query.  However, it is RECOMMENDED that Forwarders
   remember which upstream Resolving Nameservers did not return the
   option (and additional data) with their response.  The Forwarder
   SHOULD fallback to regular DNS for subsequent queries to those
   Recursive Nameservers.  It MAY switch to another Resolving Nameserver
   that does support the edns-chain-query option or try again later to
   see if the server has become less loaded and is now willing to answer
   with Query Chains.

6.  Protocol Considerations

6.1.  DNSSEC Considerations

   The presence or absence of an OPT resource record containing an edns-
   chain-query option in a DNS query does not change the usage of those
   resource records and mechanisms used to provide data origin
   authentication and data integrity to the DNS, as described in
   [RFC4033], [RFC4034] and [RFC4035].

6.2.  NS record Considerations

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   edns-chain-query responses MUST include the NS RRset from the child
   zone, which includes DNSSEC RRSIG records required for validation.

   When a DNSSEC chain is supplied via edns-chain-query, the Forwarder
   no longer requires to use the NS RRset, as it can construct the
   validation path via the DNSKEY and DS RRsets without using the NS
   RRset.  However, it is prefered that the Forwarder can populate its
   cache with this information regardless, to avoid requiring queries in
   the future just to obtain the missing NS records.  This can happen on
   a roaming device that needs to swich from using a DHCP obtained DNS
   server as forwarder to running in full autonomous resolver mode, for
   example when the DHCP obtained DNS server is broken in some way.

6.3.  TCP Session Management

   It is recommended that TCP Chain Queries are used in combination with

   Both DNS clients and servers are subject to resource constraints
   which will limit the extent to which TCP Chain Queries can be
   executed.  Effective limits for the number of active sessions that
   can be maintained on individual clients and servers should be
   established, either as configuration options or by interrogation of
   process limits imposed by the operating system.

   In the event that there is greater demand for TCP Chain Queries than
   can be accommodated, DNS servers may stop advertising the edns-query-
   chain option in successive DNS messages.  This allows, for example,
   clients with other candidate servers to query to establish new TCP
   sessions with different servers in expectation that those servers
   might still allow TCP Chain Queries.

6.4.  Non-Clean Paths

   Many paths between DNS clients and servers suffer from poor hygiene,
   limiting the free flow of DNS messages that include particular EDNS0
   options, or messages that exceed a particular size.  A fallback
   strategy similar to that described in [RFC6891] section 6.2.2 SHOULD
   be employed to avoid persistent interference due to non-clean paths.

6.5.  Anycast Considerations

   DNS servers of various types are commonly deployed using anycast

   Successive DNS transactions between a client and server using UDP
   transport may involve responses generated by different anycast nodes,
   and the use of anycast in the implementation of a DNS server is

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   effectively undetectable by the client.  The edns-chain-query option
   SHOULD NOT be included in responses using UDP transport from servers
   provisioned using anycast unless all anycast server nodes are capable
   of processing the edns-query-chain option.

   Changes in network topology between clients and anycast servers may
   cause disruption to TCP sessions making use of edns-chain-query more
   often than with TCP sessions that omit it, since the TCP sessions are
   expected to be longer-lived.  Anycast servers MAY make use of TCP
   multipath [RFC6824] to anchor the server side of the TCP connection
   to an unambiguously-unicast address in order to avoid disruption due
   to topology changes.

7.  Implementation Status

   This section records the status of known implementations of the
   protocol defined by this specification at the time of posting of this
   Internet-Draft, and is based on a proposal described in [RFC6982].
   The description of implementations in this section is intended to
   assist the IETF in its decision processes in progressing drafts to
   RFCs.  Please note that the listing of any individual implementation
   here does not imply endorsement by the IETF.  Furthermore, no effort
   has been spent to verify the information presented here that was
   supplied by IETF contributors.  This is not intended as, and must not
   be construed to be, a catalog of available implementations or their
   features.  Readers are advised to note that other implementations may

   According to [RFC6982], "this will allow reviewers and working groups
   to assign due consideration to documents that have the benefit of
   running code, which may serve as evidence of valuable experimentation
   and feedback that have made the implemented protocols more mature.
   It is up to the individual working groups to use this information as
   they see fit".

   [While there is some interest, no work has started yet]

8.  Security Considerations

8.1.  Amplification Attacks

   Chain Queries can potentially send very large DNS answers.  Attackers
   could abuse this using spoofed source IP addresses to inflict large
   Distributed Denial of Service attacks using query-chains as an
   amplification vector in their attack.  While TCP is not vulnerable
   for this type of abuse, the UDP protocol is vulnerable to this.

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   A recursive nameserver MUST NOT return Query Chain answers to clients
   over UDP without source IP address verification, for instance using
   [EASTLAKE-COOKIES].  A recursive nameserver SHOULD signal support in
   response to a Query Chain request over UDP by responding using a
   zero-length edns-chain-query option over UDO even without source IP
   address verification.

9.  Examples

9.1.  Simple Query for example.com

   1.   A web browser on a client machine asks the Forwarder running on
        localhost to resolve the A record of "www.example.com." by
        sending a regular DNS UDP query on port 53 to

   2.   The Forwarder on the client machine checks its cache, and
        notices it already has a DNSSEC validated entry of "com." in its
        cache.  This includes the DNSKEY RRset with its RRSIG records.
        In other words, according to its cache, ".com" is DNSSEC
        validated as "secure" and can be used to continue a DNSSEC
        validated chain on.

   3.   The Forwarder on the client opens a TCP connection to its
        upstream Recursive Resolver on port 53.  It adds the edns-chain-
        query option as follows:

        *  Option-code, set to [TBD]

        *  Option-length, set to 0x00 0x04

        *  Last Known Query Name set to "com."

   4.   The upstream Recursive Resolver receives a DNS query over TCP
        with the edns-chain-query Last Known Query Name set to "com.".
        After accepting the query it starts constructing a DNS reply

   5.   The upstream Recursive Resolver performs all the regular work to
        ensure it has all the answers to the query for the A record of
        "www.example.com.".  It does so without using the edns-chain-
        query option - unless it is also configured as a Forwarder.  The
        answer to the original DNS question could be the actual A
        record, the DNSSEC proof of non-existence, or an insecure
        NXDOMAIN response.

   6.   The upstream Recursive Resolver adds the edns-chain-query option
        to the DNS answer reply as follows:

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        *  Option-code, set to [TBD]

        *  Option-length, set to 0x00 0x00

        *  The Last Known Query Name is ommited (zero length)

   7.   The upstream Recursive Resolver constructs the DNS Authority
        Section and fills it with:

        *  The DS RRset for "example.com." and its corresponding RRSIGs
           (made by the "com."  DNSKEY(s))

        *  The DNSKEY RRset for "example.com." and its corresponding
           RRSIGs (made by the "example.com" DNSKEY(s))

        *  The authoritative NS RRset for "example.com." and its
           corresponding RRSIGs (from the child zone)

        If the answer does not exist, and the zone uses DNSSEC, it also
        adds the proof of non-existance, such as NSEC or NSEC3 records,
        to the Authority Section.

   8.   The upstream Recursive Resolver constructs the DNS Answer
        Section and fills it with:

        *  The A record of "www.example.com." and its corresponding

        If the answer does not exist (no-data or NXDOMAIN), the Answer
        Section remains empty.  For the NXDOMAIN case, the RCode of the
        DNS answer packet is set to NXDOMAIN.  Otherwise it remains

   9.   The upstream Recursive Resolver returns the DNS answer over the
        existing TCP connection.  When all data is sent, it SHOULD keep
        the TCP connection open to allow for additional incoming DNS
        queries - provided it has enough resources to do so.

   10.  The Forwarder receives the DNS answer.  It processes the
        Authority Section and the Answer Section and places the
        information in its local cache.  It ensures that no data is
        accepted into the cache without having proper DNSSEC validation.
        It MAY do so by looping over the entries in the Authority and
        Answer Sections.  When an entry is validated for its cache, it
        is removed from the processing list.  If an entry cannot be
        validated it is left in the process list.  When the end of the
        list is reached, the list is processed again until either all
        entries are placed in the cache, or the remaining items cannot

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        be placed in the cache due to lack of validation.  Those entries
        are then disgarded.

   11.  If the cache contains a valid answer to the application's query,
        this answer is returned to the application via a regular DNS
        answer packet.  This packet MUST NOT contain an edns-chain-query
        option.  If no valid answer can be returned, normal error
        processing is done.  For example, an NXDOMAIN or an empty Answer
        Section could be returned depending on the error condition.

9.2.  Out-of-path query for example.com

   A Recursive Resolver receives a query for the A record for
   example.com.  It includes the edns-chain-query option with the
   following parameters:

   o  Option-code, set to [TBD]

   o  Option-length, set to 0x00 0x0D

   o  The Last Known Query Name set to 'unrelated.ca.'

   As there is no chain that leads from "unrelated.ca." to
   "example.com", the Resolving Nameserver answers with RCODE "FormErr".
   It includes the edns-chain-query with the following parameters:

   o  Option-code, set to [TBD]

   o  Option-length, set to 0x00 0x00

   o  The Last Known Query Name is ommited (zero length)

9.3.  non-existent data

   A Recursive Resolver receives a query for the A record for
   "ipv6.toronto.redhat.ca".  It includes the edns-chain-query option
   with the following parameters:

   o  Option-code, set to [TBD]

   o  Option-length, set to 0x00 0x03

   o  The Last Known Query Name set to 'ca.'

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   Using regular UDP queries towards Authoritative Nameservers, it
   locates the NS RRset for "toronto.redhat.ca.".  When querying for the
   A record it receives a reply with RCODE "NoError" and an empty Answer
   Section.  The Authority Section contains NSEC3 and RRSIG records
   proving there is no A RRtype for the QNAME "ipv6.toronto.redhat.ca".

   The Recursive Resolver constructs a DNS reply with the following
   edns-chain-query option parameters:

   o  Option-code, set to [TBD]

   o  Option-length, set to 0x00 0x00

   o  The Last Known Query Name is ommited (zero length)

   The RCODE is set to "NoError".  The Authority Section is filled in

   o  The DS RRset for "redhat.ca." plus RRSIGs

   o  The DNSKEY RRset for "redhat.ca." plus RRSIGs

   o  The NS RRset for "redhat.ca." plus RRSIGs (eg ns[01].redhat.ca)

   o  The A RRset for "ns0.redhat.ca." and "ns1.redhat.ca." plus RRSIGs

   o  The DS RRset for "toronto.redhat.ca." plus RRSIGs

   o  The NS RRset for "toronto.redhat.ca." plus RRSIGs (eg

   o  The DNSKEY RRset for "toronto.redhat.ca." plus RRSIGs

   o  The A RRset and/or AAAA RRset for "ns0.toronto.redhat.ca." and
      "ns1.toronto.redhat.ca." plus RRSIGs

   o  The NSEC record for "ipv6.toronto.redhat.ca." (proves what RRTYPEs
      do exist, does not include A)

   o  The NSEC record for "toronto.redhat.ca." (proves no wildcard

   The Answer Section is empty.  The RCode is set to NOERROR.

10.  IANA Considerations

10.1.  EDNS0 option code for edns-chain-query

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   IANA has assigned option code [TBD] in the "DNS EDNS0 Option Codes
   (OPT)" registry to edns-chain-query.

11.  Acknowledgements

   Andrew Sullivan pointed out that we do not need any new data formats
   to support DNS chains.  Olafur Gudmundsson ensured the RRsets are
   returned in the proper Sections.

12.  Normative References

              Eastlake, Donald., "Domain Name System (DNS) Cookies",
              draft-eastlake-dnsext-cookies (work in progress), January

   [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.

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

   [RFC2671]  Vixie, P., "Extension Mechanisms for DNS (EDNS0)", RFC
              2671, August 1999.

   [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.

   [RFC4786]  Abley, J. and K. Lindqvist, "Operation of Anycast
              Services", BCP 126, RFC 4786, December 2006.

   [RFC6824]  Ford, A., Raiciu, C., Handley, M., and O. Bonaventure,
              "TCP Extensions for Multipath Operation with Multiple
              Addresses", RFC 6824, January 2013.

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Internet-Draft         Chain Query requests in DNS            April 2014

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

   [RFC6982]  Sheffer, Y. and A. Farrel, "Improving Awareness of Running
              Code: The Implementation Status Section", RFC 6982, July

              Wouters, P., "The edns-tcp-keepalive EDNS0 Option", draft-
              ietf-dnsop-edns-tcp-keeaplive (work in progress), April

Author's Address

   Paul Wouters
   Red Hat

   Email: pwouters@redhat.com

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