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dnsop                                                     A. Gulbrandsen
Internet-Draft
Intended status: Standards Track                                  J. Yao
Expires: August 16, 2019                                           CNNIC
                                                       February 12, 2019


     Decreasing Fetch time of Root Data by Additional Caching Rules
               draft-arnt-yao-dnsop-root-data-caching-00

Abstract

   Some DNS recursive resolvers have long round trip times to the
   nearest DSN root server, which has been an obstacle to DNS query
   performance.  In order to decrease root record fetch time without
   introducing a new source of errors, this document proposes a root-
   specific modification to the caching rules.

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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   Internet-Drafts are draft documents valid for a maximum of six months
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   This Internet-Draft will expire on August 16, 2019.

Copyright Notice

   Copyright (c) 2019 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
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   publication of this document.  Please review these documents
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   include Simplified BSD License text as described in Section 4.e of




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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   2
   3.  Design Considerations . . . . . . . . . . . . . . . . . . . .   3
   4.  Changes . . . . . . . . . . . . . . . . . . . . . . . . . . .   3
     4.1.  Impact on the resolver  . . . . . . . . . . . . . . . . .   3
     4.2.  Impact on the root servers  . . . . . . . . . . . . . . .   4
     4.3.  Impact on the network . . . . . . . . . . . . . . . . . .   4
   5.  System Requirements . . . . . . . . . . . . . . . . . . . . .   4
   6.  Difference between this mechanism and RFC7706 based mechanism   4
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   8.  Change History  . . . . . . . . . . . . . . . . . . . . . . .   4
     8.1.  draft-arnt-yao-dnsop-root-data-caching: Version 00  . . .   5
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .   5
     9.2.  Informative References  . . . . . . . . . . . . . . . . .   5
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Introduction

   Some DNS recursive resolvers suffer from long round trip times to the
   nearest DSN root server, which has been an obstacle to DNS query
   performance.

   A particular characteristic of the root zone is that when cached, its
   data is usable for very different queries: An MTA that wishes to send
   mail to Google needs the NS records for .com, and so does a web
   browser that wishes to open the Bing home page.  Other public zones
   (such as .co.uk and .gen.nz, and perhaps tumblr.com) are shared among
   some queries, the root zone is used for all.

   This suggests that caching rules that are appropriate to the rest of
   the DNS tree may not be ideal for the root zone.

   We propose to refresh root zone data probabilistically when it
   expires, instead of when needed.

2.  Terminology

   The basic key words such as "MUST", "MUST NOT", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "MAY", and "MAYNOT" are to be interpreted as
   described in [RFC2119].





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   The basic DNS terms used in this specification are defined in the
   documents [RFC1034] and [RFC1035].

3.  Design Considerations

   o  The RRs in the root zone do not change frequently.

   o  The root zone is not large, compared to the RAM of even smallish
      resolvers.

   o  DNSSEC[RFC4033][RFC4034][RFC4035] protects the data origin
      authentication and data integrity.

4.  Changes

   When an RR in a resolver's cache expires and is in the root zone,
   then the resolver immediately refreshes it.  There are no protocol
   changes or extensions.

   Assuming that the lookup frequency for a root-zone RR drops by half
   for every additional week, (ie. half of all RRs that looked up
   repeatedly are looked up every week, a quarter every second week, an
   eighth every third week, etc), this eliminates root-zone delay as a
   timing factor for more than 99.999% of queries through this resolver.

   In practice, this should mean that unintentional clearing of the
   resolver's cache (e.g. as a side effect of restarting the resolver)
   is the next biggest contributor to slow queries.

   OPEN ISSUE: Or perhaps better, only with 95% likelihood?  If the
   resolver refreshes it with 100% certainty, then the resolver
   necessarily grows to storing all of the root-zone RRs it has needed
   forever.  If the resolver refreshes it 95% of the time and root-zone
   RRs have a TTL of around a week, then an unused root-zone RR has
   around 50% chance of being discarded after three months.  The
   resolver will perform around 12 DNS queries that turn out, in
   hindsight, not to be necessary.  The text below assumes 95%
   likelihood.

4.1.  Impact on the resolver

   The resolver is able to answer DNS queries quickly for all root RRs
   that have been used in the past several months, instead of the past
   week.  The cost in additional processing and RAM is negligible; there
   are no additional tasks that can go wrong.






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4.2.  Impact on the root servers

   The root servers one additional query per TTL (usually week) per
   resolver and RR, for the RRs that have been needed by that resolver
   in the past, but will not be needed in the coming week.  The queries
   arrive evenly.  They do not peak around a particular time, but are
   distributed as the normal traffic.

4.3.  Impact on the network

   There is no additional network traffic related to ongoing use of the
   network (or DNS).  There are also no savings.  However, some packets
   are sent earlier than they would be withot this document.

   Around 25 additional packets are transmitted (two per week over a
   period of some months) when a the users of a particular resolver stop
   using a particular root-zone RR.

5.  System Requirements

   In order to implement the mechanism described in this document:

   o  The system MUST be able to validate DNSSEC resource records.

   o  The system MUST have an up-to-date copy of the DNS root key.

6.  Difference between this mechanism and RFC7706 based mechanism

   The following features are considered to be different compared to
   RFC7706 based mechanism:

   o  This document retrieves single RRs (or probably sets, as required
      by DNSSSEC validation).  RFC7706 retrieves the entire zone.

   o  This document requires no actions by human administrators.

   o  This document provides only a probabilistic performance
      improvement; RFC 7706 provides a guarantee.

7.  Security Considerations

   None.

8.  Change History

   RFC Editor: Please remove this section.





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8.1.  draft-arnt-yao-dnsop-root-data-caching: Version 00

   o  Decreasing fetch time of root data by additional caching rules

9.  References

9.1.  Normative References

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

   [RFC1035]  Mockapetris, P., "Domain names - implementation and
              specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,
              November 1987, <https://www.rfc-editor.org/info/rfc1035>.

   [RFC1321]  Rivest, R., "The MD5 Message-Digest Algorithm", RFC 1321,
              DOI 10.17487/RFC1321, April 1992,
              <https://www.rfc-editor.org/info/rfc1321>.

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

   [RFC4033]  Arends, R., Austein, R., Larson, M., Massey, D., and S.
              Rose, "DNS Security Introduction and Requirements",
              RFC 4033, DOI 10.17487/RFC4033, March 2005,
              <https://www.rfc-editor.org/info/rfc4033>.

   [RFC4034]  Arends, R., Austein, R., Larson, M., Massey, D., and S.
              Rose, "Resource Records for the DNS Security Extensions",
              RFC 4034, DOI 10.17487/RFC4034, March 2005,
              <https://www.rfc-editor.org/info/rfc4034>.

   [RFC4035]  Arends, R., Austein, R., Larson, M., Massey, D., and S.
              Rose, "Protocol Modifications for the DNS Security
              Extensions", RFC 4035, DOI 10.17487/RFC4035, March 2005,
              <https://www.rfc-editor.org/info/rfc4035>.

9.2.  Informative References

   [Root-loopback]
              Kumari, W. and P. Hoffman, "Decreasing Access Time to Root
              Servers by Running One on Loopback", November 2015,
              <https://tools.ietf.org/html/rfc7706>.





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Authors' Addresses

   Arnt Gulbrandsen

   Email: arnt@gulbrandsen.priv.no


   Jiankang Yao
   CNNIC
   4 South 4th     Street,Zhongguancun,Haidian     District
   Beijing, Beijing  100190
   China

   Phone: +86 10   5881 3007
   Email: yaojk@cnnic.cn




































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