Internet DRAFT - draft-pfrc-2181-ttl
draft-pfrc-2181-ttl
INTERNET-DRAFT Declan Ma, Ed.
Intended Status: Proposed Standard zDNS Ltd.
Expires: 2015-10-15 2015-05-27
DNS Resource Record TTL
draft-pfrc-2181-ttl-00
Abstract
RFC 2181 collected eight independent considerations and created a single
docuement to address each of them in turn. Over the following two decades
it has become clear that each of these items should be considered and evovolve
in its own right, as suggested in RFC 2181. This document extracts the exact
text from RFC 2181 and places it into its own track.
Status of this Memo
This Internet-Draft is submitted to IETF 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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Copyright and License Notice
Copyright (c) 2015 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
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
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include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2 Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3 Time to Live (TTL) . . . . . . . . . . . . . . . . . . . . . . 3
4 Security Considerations . . . . . . . . . . . . . . . . . . . . 3
5 References . . . . . . . . . . . . . . . . . . . . . . . . . . 3
6 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 4
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1 Introduction
This document is intended to give the precise definition of the DNS
resource record Time to Live (TTL).
2 Terminology
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 RFC 2119 [RFC2119].
3 Time to Live (TTL)
The definition of values appropriate to the TTL field in STD 13 is
not as clear as it could be, with respect to how many significant
bits exist, and whether the value is signed or unsigned. It is
hereby specified that a TTL value is an unsigned number, with a
minimum value of 0, and a maximum value of 2147483647. That is, a
maximum of 2^31 - 1. When transmitted, this value shall be encoded
in the less significant 31 bits of the 32 bit TTL field, with the
most significant, or sign, bit set to zero.
Implementations should treat TTL values received with the most
significant bit set as if the entire value received was zero.
Implementations are always free to place an upper bound on any TTL
received, and treat any larger values as if they were that upper
bound. The TTL specifies a maximum time to live, not a mandatory
time to live.
4 Security Considerations
It may be observed that in section 3.2.1 of RFC1035, which defines
the format of a Resource Record, that the definition of the TTL field
contains a throw away line which states that the TTL of an SOA record
should always be sent as zero to prevent caching. This is mentioned
nowhere else, and has not generally been implemented. Implementations
should not assume that SOA records will have a TTL of zero, nor are
they required to send SOA records with a TTL of zero.
5 References
[RFC1034] Mockapetris, P., "Domain names - concepts and facilities",
STD 13, RFC 1034, November 1987.
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[RFC1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, November 1987.
[RFC2199] Ramos, A., "Request for Comments Summary RFC Numbers 2100-
2199", RFC 2199, January 1998.
6 Authors' Addresses
Declan Ma, Ed.
ZDNS Ltd.
4, South 4th Street, Zhongguancun,
Haidian, Beijing 100190,
China
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