Internet DRAFT - draft-pfrc-2181-tc-bit

draft-pfrc-2181-tc-bit



 



INTERNET-DRAFT                                       Declan Ma, Ed.
Intended Status: Proposed Standard                        zDNS Ltd.
Expires: 2015-10-15                                      2015-05-27


         Use of the TC (Truncated) Header Bit for DNS Responses
                       draft-pfrc-2181-tc-bit-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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   Internet-Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
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   time.  It is inappropriate to use Internet-Drafts as reference
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   The list of current Internet-Drafts can be accessed at
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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  The TC (truncated) header bit . . . . . . . . . . . . . . . . .  3
   4  Security Considerations . . . . . . . . . . . . . . . . . . . .  3
   5  References  . . . . . . . . . . . . . . . . . . . . . . . . . .  3
   6  Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . .  4


































 


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1  Introduction

   This document is intended to clarify the use of the TC (truncated)
   header bit for DNS Responses.

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  The TC (truncated) header bit

   The TC bit should be set in responses only when an RRSet is required
   as a part of the response, but could not be included in its entirety.
   The TC bit should not be set merely because some extra information
   could have been included, but there was insufficient room.  This
   includes the results of additional section processing.  In such cases
   the entire RRSet that will not fit in the response should be omitted,
   and the reply sent as is, with the TC bit clear.  If the recipient of
   the reply needs the omitted data, it can construct a query for that
   data and send that separately.

   Where TC is set, the partial RRSet that would not completely fit may
   be left in the response.  When a DNS client receives a reply with TC
   set, it should ignore that response, and query again, using a
   mechanism, such as a TCP connection, that will permit larger replies.


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.

   [RFC1035]  Mockapetris, P., "Domain names - implementation and
              specification", STD 13, RFC 1035, November 1987.

 


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   [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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