INTERNET-DRAFT Declan Ma, Ed. Intended Status: Proposed Standard zDNS Ltd. Expires: 2015-10-15 2015-05-22 Use of the TC (Truncated) Header Bit for DNS Responses draft-bill-dnsop-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 other groups may also distribute working documents as Internet-Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/1id-abstracts.html The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html 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 Declan Ma, Ed. Expires 2015-10-15 [Page 1] INTERNET DRAFT Use of the TC Header Bit for DNS Responses 2015-05-22 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 Declan Ma, Ed. Expires 2015-10-15 [Page 2] INTERNET DRAFT Use of the TC Header Bit for DNS Responses 2015-05-22 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. Declan Ma, Ed. Expires 2015-10-15 [Page 3] INTERNET DRAFT Use of the TC Header Bit for DNS Responses 2015-05-22 [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 Declan Ma, Ed. Expires 2015-10-15 [Page 4]