Returning extra answers in DNS responses.
draft-wkumari-dnsop-multiple-responses-05

Versions: 00 01 02 03 04 05                                             
dnsop                                                          W. Kumari
Internet-Draft                                                    Google
Intended status: Standards Track                                  Z. Yan
Expires: July 8, 2016                                              CNNIC
                                                             W. Hardaker
                                                           Parsons, Inc.
                                                        January 05, 2016


              Returning multiple answers in DNS responses.
               draft-wkumari-dnsop-multiple-responses-02

Abstract

   This document (re)introduces the ability to provide multiple answers
   in a DNS response.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on July 8, 2016.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements notation . . . . . . . . . . . . . . . . . .   3
   2.  Background  . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   4.  Returning multiple answers  . . . . . . . . . . . . . . . . .   3
   5.  Additional records pseudo-RR  . . . . . . . . . . . . . . . .   5
     5.1.  File Format . . . . . . . . . . . . . . . . . . . . . . .   5
     5.2.  Wire Format . . . . . . . . . . . . . . . . . . . . . . .   5
   6.  Signaling support . . . . . . . . . . . . . . . . . . . . . .   6
   7.  Stub-Resolver Considerations  . . . . . . . . . . . . . . . .   6
   8.  Use of Additional information . . . . . . . . . . . . . . . .   6
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
   10. Security Considerations . . . . . . . . . . . . . . . . . . .   7
   11. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   7
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . .   7
     12.1.  Normative References . . . . . . . . . . . . . . . . . .   7
     12.2.  Informative References . . . . . . . . . . . . . . . . .   8
   Appendix A.  Changes / Author Notes.  . . . . . . . . . . . . . .   8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   8

1.  Introduction

   Often the name being resolved in the DNS provides information about
   why the name is being resolved, allowing the nameserver to predict
   what other answers the client will soon query for.  By providing
   multiple answers in the response, the authoritative name server
   operator can ensure that the recursive server that the client is
   using has all the answers in its cache.

   For example, the name server operator of Example Widgets, Inc
   (example.com) knows that the example.com web page at www.example.com
   contains various other resources, including some images (served from
   images.example.com), some Cascading Style Sheets (served from
   css.example.com) and some JavaScript (data.example.com).  A client
   attempting to resolve www.example.com is very likely to be a web
   browser rendering the page and so will need to also resolve all of
   the other names to obtain these other resources.  Providing all of
   these answers in response to a query for www.example.com allows the
   recursive server to populate its cache and have all of the answers
   available when the client asks for them.

   Other examples where this technique is useful include SMTP (including
   the mail server address when serving the MX record), SRV (providing
   the target information in addition to the SRV response) and TLSA
   (providing any TLSA records associated with a name).




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   This is purely an optimization - by providing all of other, related
   answers that the client is likely to need along with the answer that
   they requested, users get a better experience, iterative servers need
   to perform less queries, authoritative servers have to answer fewer
   queries, etc.

1.1.  Requirements notation

   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].

2.  Background

   The existing DNS specifications allow for additional information to
   be included in the "additional" section of the DNS response, but in
   order to defeat cache poisoning attacks most implementations either
   ignore or don't trust additional information (other than for "glue").
   For some more background, see [Ref.Bellovin], [RFC1034], [RFC2181].

   Not trusting the information in the additional section was necessary
   because there was no way to authenticate it.  If you queried for
   www.example.com and got back answers for www.invalid.com you couldn't
   tell if these were actually from invalid.com or if an attacker was
   trying to get bad information for invalid.com into your cache.  In a
   world of ubiquitous DNSSEC deployment [Ed note: By the time this
   document is published, there *will* be ubiquitous DNSSEC :-) ] the
   iterative server can validate the information and trust it.

3.  Terminology

   Additional records  Additional records are records that the
      authoritative nameserver has included in the Additional section.

   Primary query  A Primary query (or primary question) is a QNAME that
      the name server operator would like to return additional answers
      for.

   Supporting information  Supporting information is the DNSSEC RRSIGs
      that prove the authenticity of the Additional records.

4.  Returning multiple answers

   The authoritative nameserver should include as many of the instructed
   Additional records and Supporting information as will fit in the
   response packet.





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   In order to include Additional records in a response, certain
   conditions need to be met.  [Ed note: Some discussion on each rule is
   below]

   1.  Additional records MUST only be included when the primary name
       and each additional record are signed using DNSSEC "valid".

   2.  Additional records MUST only be served over TCP connections, or
       when DNS Cookies [ToDo: Ref] are in use.  This is to mitigate
       Denial of Service reflection attacks.[1]

   3.  Additional records SHOULD be contained within the same zone as
       the primary name[2], or MAY be additionally be contained within a
       child zone for which the name server is authoritative for,
       assuming all DNSSEC validation records required to validate the
       child(ren) are included as well.  Note that the DS record, and NS
       and glue records for a child zone may be returned even when no
       other additional data for the child will be included.

   4.  The DNSSEC supporting information necessary to perform validation
       on the records must be included.  I.E., the RRSIGs required to
       validate the Additional record information must be included.

   5.  The authoritative nameserver SHOULD include as many of the
       additional records as will fit in the response.  Each Additional
       record MUST have its matching Supporting information.  Additional
       records MUST be inserted in the order specified in the Additional
       records list.

   6.  Operators SHOULD only include Additional answers that they expect
       a client to actually need. [3]

   [Ed note 1: The above MAY be troll bait.  I'm not really sure if this
   is a good idea or not - moving folk towards TCP is probably a good
   idea, and this is somewhat of an optional record type.  Then again,
   special handing (TCP only) for a record would be unusual.  Additional
   records could cause responses to become really large, but there are
   already enough large records that can be used for reflection attacks
   that we can just give up on the whole "keep responses as small as
   possible" ship.  ]

   [Ed note 2: This is poorly worded.  I mumbled about bailiwick,
   subdomains, etc but nothing I could come up with was better.  Also,
   is this rule actually needed?  I *think* it would be bad for .com
   servers to be able to include Additional records for
   www.foo.bar.baz.example.com, but perhaps <handwave>public-suffix-
   list?! This rule also makes it easier to decide what all DNSSEC
   information is required.]



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   [Ed note 3: This is not enforceable. ]

5.  Additional records pseudo-RR

   To allow the authoritative nameserver operator to configure the name
   server with the additional records to serve when it receives a query
   to a label, we introduce the Additional Resource Record (RR).

5.1.  File Format

   The format of the Additional RR is:

   label ADD "label,type; label,type; label,type; ..."

   For example, if the operator of example.com would like to also return
   A record answers for images.example.com, css.html.example.com and
   both an A and AAAA for data.example.com when queried for
   www.example.com he would enter:

   www ADD "images,A; css.html,A; data,A; data,AAA;"

   The entries in the ADD list are ordered.  An authoritative nameserver
   SHOULD insert the records in the order listed when filling the
   response packet.  This is to allow the operator to express a
   preference in case all the records to not fit.  The TTL of the
   records added to the Additional section are MUST be the same as if
   queried directly.

   In some cases the operator might not know what all additional records
   clients need.  For example, the owner of www.example.com may have
   outsourced his DNS operations to a third party.  DNS operators may be
   able to mine their query logs, and see that, in a large majority of
   cases, a recursive server asks for foo.example.com and then very soon
   after asks for bar.example.com, and so may decide to optimize this by
   opportunistically returning bar when queried for foo.  This
   functionality could also be included in the authoritative name server
   software itself, but discussions of these re outside the scope of
   this document.

5.2.  Wire Format

   The wire format of the Additional RR is the same as the wire format
   for a TXT RR:

       +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
       /                   TXT-DATA                    /
       +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+




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   Where TXT-DATA is one or more charter-strings.

   The Additional RR has RR type TBD [RFC Editor: insert the IANA
   assigned value and delete this note]

6.  Signaling support

   Iterative nameservers that support Additional records signal this by
   setting the OPT record's PL ("plus") bit (bit NN [TBD: assigned by
   IANA] in the EDNS0 extension header to 1.

7.  Stub-Resolver Considerations

   No modifications need to be made to stub-resolvers to get the
   predominate benefit of this protocol, since the majority of the speed
   gain will take place between the validating recursive resolver and
   the authoritative name server.  However, stub resolvers may wish to
   query directly for the Additional RR if it wants to pre-query for
   data that will likely be needed in the process of supporting its
   application.

8.  Use of Additional information

   When receiving Additional information, an iterative server follows
   certain rules:

   1.  Additional records MUST be validated before being used.

   2.  Additional records SHOULD be annotated in the cache as having
       been received as Additional records.

   3.  Additional records SHOULD have lower priority in the cache than
       answers received because they were requested.  This is to help
       evict Additional records from the cache first, and help stop
       cache filling attacks.

   4.  Iterative servers MAY choose to ignore Additional records for any
       reason, including CPU or cache space concerns, phase of the moon,
       etc.  It may choose to only accept all, some or none of the
       Additional records.

9.  IANA Considerations

   This document contains the following IANA assignment requirements:

   1.  The PL bit discussed in Section 6 needs to be allocated.





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10.  Security Considerations

   Additional records will make DNS responses even larger than they are
   currently, leading to more large records that can be used for DNS
   reflection attacks.  We mitigate this by only serving these over TCP.

   A malicious authoritative server could include a large number of
   Additional records (and associated DNSSEC information) and attempt to
   DoS the recursive by making it do lots of DNSSEC validation.  I don't
   view this as a very serious threat (CPU for validation is cheap
   compared to bandwidth), but we mitigate this by allowing the
   iterative to ignore Additional records whenever it wants.

   By requiring the ALL of the Additional records are signed, and all
   necessary DNSSEC information for validation be included we avoid
   cache poisoning (I hope :-))

11.  Acknowledgements

   The authors wish to thank some folk.

12.  References

12.1.  Normative References

   [Ref.Bellovin]
              Bellovin, S., "Using the Domain Name System for System
              Break-Ins", 1995,
              <https://www.cs.columbia.edu/~smb/papers/dnshack.pdf>.

   [RFC1034]  Mockapetris, P., "Domain names - concepts and facilities",
              STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987,
              <http://www.rfc-editor.org/info/rfc1034>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/
              RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

   [RFC2181]  Elz, R. and R. Bush, "Clarifications to the DNS
              Specification", RFC 2181, DOI 10.17487/RFC2181, July 1997,
              <http://www.rfc-editor.org/info/rfc2181>.

   [RFC5395]  Eastlake 3rd, D., "Domain Name System (DNS) IANA
              Considerations", RFC 5395, DOI 10.17487/RFC5395, November
              2008, <http://www.rfc-editor.org/info/rfc5395>.





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12.2.  Informative References

   [I-D.ietf-sidr-iana-objects]
              Manderson, T., Vegoda, L., and S. Kent, "RPKI Objects
              issued by IANA", draft-ietf-sidr-iana-objects-03 (work in
              progress), May 2011.

Appendix A.  Changes / Author Notes.

   [RFC Editor: Please remove this section before publication ]

   From -00 to -01.

   o  Nothing changed in the template!

Authors' Addresses

   Warren Kumari
   Google
   1600 Amphitheatre Parkway
   Mountain View, CA  94043
   US

   Email: warren@kumari.net


   Zhiwei Yan
   CNNIC
   No.4 South 4th Street, Zhongguancun
   Beijing  100190
   P. R. China

   Email: yanzhiwei@cnnic.cn


   Wes Hardaker
   Parsons, Inc.
   P.O. Box 382
   Davis, CA  95617
   US

   Email: ietf@hardakers.net









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