Internet DRAFT - draft-wkumari-dnsop-ttl-stretching
draft-wkumari-dnsop-ttl-stretching
Network Working Group W. Kumari
Internet-Draft Google
Intended status: Informational November 14, 2016
Expires: May 18, 2017
Stretching DNS TTLs
draft-wkumari-dnsop-ttl-stretching-00
Abstract
The TTL of a DNS Resource Record expresses how long a record may be
cached before it should be discarded. This document discusses the
possibility of "stretching TTLS" (using them past their expiration)
if they cannot be refreshed. This works on the assumption that stale
data may be better than no data.
PLEASE NOTE: This document is a strawman to drive discussion. It may
or may not be a good idea; this document documents the idea so that
there is something concrete to throw tomatoes at.
[ Ed note: Text inside square brackets ([]) is additional background
information, answers to frequently asked questions, general musings,
etc. They will be removed before publication. This document is
being collaborated on in Github at: https://github.com/wkumari/draft-
wkumari-dnsop-ttl-stretching. The most recent version of the
document, open issues, etc should all be available here. The authors
(gratefully) accept pull requests ]
Status of This Memo
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This Internet-Draft will expire on May 18, 2017.
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Copyright Notice
Copyright (c) 2016 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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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements notation . . . . . . . . . . . . . . . . . . 3
2. Proposal . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 3
4. Security Considerations . . . . . . . . . . . . . . . . . . . 3
5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 3
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 3
6.1. Normative References . . . . . . . . . . . . . . . . . . 3
6.2. Informative References . . . . . . . . . . . . . . . . . 4
Appendix A. Changes / Author Notes. . . . . . . . . . . . . . . 4
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 4
1. Introduction
DNS Resource Records (RR) have an associated TTL. This is how long
the record may be cached before it should be expired and new
information fetched. This is based upon the assumption that the
authoritative servers will be reachable when they are needed, and
that records expire and are immediately evicted from the cache.
There are a number of reasons why an authoritative server may become
unreachable, including, unfortunately, Denial of Service (DoS)
attacks. Recent proposals, for example "Highly Automated Method for
Maintaining Expiring Records" ([I-D.wkumari-dnsop-hammer]) propose
refreshing records in the cache before they expire and are evicted.
This means that the recursive server still has information in its
cache when it attempts to contact the authoritative server.
This document suggests that, if the recursive server is unable to
contact the authoritative server, it simply extends the existing
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records TTL, on the assumption that "stale bread if better than no
bread".
[Ed: This is the primary point of the document / question -- if you
cannot reach the authoritative nameservers (perhaps they being DoS-
ed, perhaps they were unplugged, you cannot really tell) it is better
to use the last known (and perhaps outdated) information, or is it
better for the domain to go dark? I think the former, but this is a
significant change to the meaning / semantics of TTLs).
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. Proposal
If a recursive nameserver is unable to contact any of the
authoritative nameservers for a zone, and it still has the resource
record cached, it MAY "stretch" the TTL by simply increasing it it by
the original TTL. It may do this N times, where N should be
configurable.
[ Ed: I was going to say "by doubling the TTL", but then if we allow
implementations to do this e.g 3 times, is that 4 times the original
TTL, or is it 2^3 the original TTL].
3. IANA Considerations
This document contains no IANA considerations.Template: Fill this in!
4. Security Considerations
TODO: Fill this out!
5. Acknowledgements
The authors wish to thank some folk.
6. References
6.1. Normative References
[IANA.AS_Numbers]
IANA, "Autonomous System (AS) Numbers",
<http://www.iana.org/assignments/as-numbers>.
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[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>.
6.2. 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.
[I-D.wkumari-dnsop-hammer]
Kumari, W., Arends, R., and S. Woolf, "Highly Automated
Method for Maintaining Expiring Records", draft-wkumari-
dnsop-hammer-00 (work in progress), July 2013.
Appendix A. Changes / Author Notes.
[RFC Editor: Please remove this section before publication ]
From -00 to -01
o Nothing changed in the template!
Author's Address
Warren Kumari
Google
1600 Amphitheatre Parkway
Mountain View, CA 94043
US
Email: warren@kumari.net
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