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
   Task Force (IETF), its areas, and its working groups.  Note that
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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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