Internet DRAFT - draft-arnt-yao-dnsop-root-data-caching
draft-arnt-yao-dnsop-root-data-caching
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
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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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