dnsop                                                         P. Wouters
Internet-Draft                                                   Red Hat
Intended status: Standards Track                          March 09,                        October 03, 2015
Expires: September 10, 2015 April 05, 2016

                      Chain Query requests in DNS


   This document defines an EDNS0 extension that can be used by a
   security-aware validating Resolver configured as a Forwarder to send
   a single query, requesting a complete validation path along with the
   regular query answer.  The reduction in queries lowers the latency.
   This extension requries the use of source IP verified transport such
   as TCP or UDP with DNS-COOKIES so it cannot be abused in
   amplification attacks.

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
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   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
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   This Internet-Draft will expire on September 10, 2015. April 05, 2016.

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   document authors.  All rights reserved.

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Table of Contents

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

1.  Introduction

   Traditionally, a DNS client operates in stub-mode.  For each DNS
   question the DNS client needs to resolve, it sends a single query to
   an upstream Recursive Resolver to obtain a single DNS answer.  When
   DNSSEC [RFC4033] is deployed on such DNS 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.

   Currently, applications 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 set of UDP questions will result in all the records
   required for DNSSEC validation.  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
   Resolver running as a Forwarder to open a TCP connection to another
   Resolver and request a DNS chain answer using one DNS query/answer
   pair.  This reduces the number of round-trip times ("RTT") to two.
   If combined with long livd TCP or [TCP-KEEPALIVE] there is only 1
   RTT.  While the upstream 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 DNS 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 Recursive Resolver has to perform.

   This EDNS0 extension is only intended to be sent by Forwarders to
   Recursive Resolvers.  It can (and should be) ignored by Authoritative

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

   The DNS terminology used in this document is that of
   [DNS-TERMINOLOGY].  Additionally, the following terms are used:
   [edit: which I hope will end up in the terminology document]

   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.  Also known as "security-aware

3.  Overview
   When DNSSEC is deployed on the host, it can no longer delegate all
   DNS work to the upstream Recursive Resolver.  Obtaining just the DNS
   answer itself is not enough to validate that answer using DNSSEC.
   For DNSSEC validation, the DNS client requires a locally running
   validating Resolver so it can confirm DNSSEC validation of all
   intermediary DNS answers.  It can configure itself as a DNS Forwarder
   if it obtains the IP addresses of one or more Recursive Resolvers
   that are available, or as a stand-alone Recursive Resolver if no
   functional Recursive Resolvers were obtained.  Generating the
   required queries for validation adds a significant delay in answering
   the DNS question of the locally running application.  The application
   must wait while the Resolver validates all intermediate answers.
   Each round-trip adds to the total time waiting on DNS resolution with
   validation to complete.  This makes DNSSEC resolving impractical for
   devices on networks with a high latency.

   The edns-chain-query option allows the Resolver to request all
   intermediate DNS data it requires to resolve and validate a
   particular DNS answer in a single round-trip.  The Resolver could be
   part of the application or a Recursive Resolver running on the host.

   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.

   Applications that support edns-chain-query internally can perform
   validation without requiring the host the run a Recursive Resolver.
   This is particularly useful for virtual servers in a cloud or
   container based deployment where it is undesirable to run a Recursive
   Resolver per virtual machine.

   The format of this option is described in Section 4.

   As described in Section 5.4, a Recursive Resolver could use this
   EDNS0 option to include additional data required by the Resolver 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.

4.  Option Format

   This draft uses an EDNS0 [RFC6891] 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  OPTION-CODE, 2 octets, for edns-chain-query is [TBD].

   o  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

5.  Protocol Description

5.1.  Discovery of Support

   A DNS Forwarder may include a zero-length edns-chain-query option in
   queries over any transport to discover the DNS server capability for
   edns-chain-query.  Recursive Resolvers that support and are willing
   to accept chain queries over source IP verified transport respond to
   a zero-length edns-chain-query received by including a zero-length
   edns-chain-query option in the answer.  A DNS Forwarder MAY then
   switch to a source IP verified transport and sent a non-zero edns-
   chain-query value to request a chain-query response from the
   Recursive Resolver.  Examples of source IP verification is the 3-way
   TCP handshake and UDP with [DNS-COOKIES].

5.2.  Generate a Query
   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 9.1.

   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.  A separate
   query should be send for the remainder of the validation chain.

   The edns-chain-query option should generally be sent by system
   Forwarders and Resolvers within an application that also perform
   DNSSEC validation.

5.3.  Send the Option

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

   A DNS Forwarder can request the edns-chain-query option with every
   outgoing DNS query.  However, it is RECOMMENDED that DNS Forwarders
   remember which upstream Recursive Resolvers did not return the option
   (and additional data) with their response.  The DNS Forwarder SHOULD
   fallback to regular DNS for subsequent queries to those Recursive
   Resolvers.  It MAY switch to another Resolving Resolver 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

5.4.  Generate a Response

   When a query containing a non-zero edns-chain-query option is
   received from a DNS 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 in the DNS
   answer packet with the DNS RRSets required for validating the answer.
   The DNS RRsets added start with the first chain element below the
   received Last Known Query Name up to 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 the traditional DNS
   answer.  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 or willing to support Chain
   Queries at this time.

   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 [RFC6891].

   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 [RFC6891].  This refusal can be used for chains that
   would be too big or chains that would reveal too much information
   considered private.

   At any time, a Recursive Resolver that has determined that it is
   running low on resources can refuse to acknowledge a Chain Query by
   omitting the edns-chain-query option in its reply.  It may do so even
   if it conveyed support to a DNS client previously.  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 Recursive Resolver 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 are also
   added to the Authority Section.

   The response from a Recursive Resolver to a Resolver MUST NOT contain
   the edns-chain-query option if none was present in the Resolver's
   original request.

   A DNS query that contains the edns-chain-query option MUST also have
   the DNSSEC OK bit set.  If this bit is not set, the edns-chain-query
   option received MUST be ignored.

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

   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 DNS
   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, the DNS Forwarder might be forced to switch from
   Forwarder mode to Recursive Resolver mode due to a network topology
   change.  In Recursive Resolver mode, it requires the NS RRsets to
   find and query Authoritative Servers directly.  It is preferred that
   the DNS Forwarder populate its cache with this information to avoid
   requiring future queries to obtain any missing NS records.  Therefor,
   edns-chain-query responses MUST include the NS RRset from the child
   zone, which includes DNSSEC RRSIG records required for validation.

6.3.  TCP Session Management

   It is recommended that TCP sessions to the Recursive Resolver are not
   immediately closed after the DNS answer to the first query is
   received.  It is recommended to use [TCP-KEEPALIVE].

   Both DNS clients and servers are subject to resource constraints
   which will limit the extent to which 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 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
   sessions with different servers in expectation that those servers
   might still allow Chain Queries.

6.4.  Non-Clean Paths

   Many paths between DNS clients and Recursive Resolvers 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

   Recursive Resolvers of various types are commonly deployed using
   anycast [RFC4786].

   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
   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.

   A Recursive Resolver MUST NOT return Query Chain answers to clients
   over UDP without source IP address verification.  An example of UDP
   based source IP address verification is [DNS-COOKIES].  A Recursive
   Resolver refusing a Query Chain request MUST ignore the ends-query-
   chain option and answering the DNS request as if it was received
   without the ends-query-chain option.  It MUST NOT send an RCODE of

   A Recursive Resolver SHOULD signal support in response to a zero-
   length edns-chain-query request over UDP by responding with an zero-
   length edns-chain-query option even without source IP address
   verification.  This allows a client to detect edns-chain-query
   support without the need for [DNS-COOKIES] or TCP.

9.  Examples

9.1.  Simple Query for example.com

   o  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

   o  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.

   o  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."

   o  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 packet.

   o  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.

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

      *  Option-code, set to [TBD]

      *  Option-length, set to 0x00 0x00

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

   o  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.

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

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

   o  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.

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

   o  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.'

   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

   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.  Thanks to Tim Wicinski for his
   thorough review.

12.  Normative References

              Eastlake, Donald., "Domain Name System (DNS) Cookies",
              draft-ietf-dnsop-cookies (work in progress), February August 2015.

              Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS
              Terminology", draft-hoffman-dns-terminology (work in
              progress), March 2015.

   [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.

   [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, DOI 10.17487/RFC4786,
              December 2006. 2006, <http://www.rfc-editor.org/info/rfc4786>.

   [RFC6824]  Ford, A., Raiciu, C., Handley, M., and O. Bonaventure,
              "TCP Extensions for Multipath Operation with Multiple
              Addresses", RFC 6824, DOI 10.17487/RFC6824, January 2013. 2013,

   [RFC6891]  Damas, J., Graff, M., and P. Vixie, "Extension Mechanisms
              for DNS (EDNS(0))", STD 75, RFC 6891, DOI 10.17487/
              RFC6891, April 2013. 2013,

   [RFC6982]  Sheffer, Y. and A. Farrel, "Improving Awareness of Running
              Code: The Implementation Status Section", RFC 6982, DOI
              10.17487/RFC6982, July
              2013. 2013,

              Wouters, P., "The edns-tcp-keepalive EDNS0 Option", draft-
              wouters-edns-tcp-keeaplive (work in progress), February

Author's Address

   Paul Wouters
   Red Hat

   Email: pwouters@redhat.com