Network Working Group R. Bellis Internet-Draft Nominet UK Updates: 6891 (if approved) October 24, 2014 Intended status: Standards Track Expires: April 27, 2015 Connection Close Signalling for DNS draft-bellis-dnsop-connection-close-00 Abstract This document updates [RFC6891] by specifying a new single-bit flag in a DNS response that when seen in a packet carried over a connection-orientated transport protocol indicates to the client that it should close the current connection. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. 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." This Internet-Draft will expire on April 27, 2015. Copyright Notice Copyright (c) 2014 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 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. Bellis Expires April 27, 2015 [Page 1] Internet-Draft Connection Close Signalling for DNS October 2014 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 2 3. Specification . . . . . . . . . . . . . . . . . . . . . . . . 3 4. Connection Handling . . . . . . . . . . . . . . . . . . . . . 3 4.1. Servers . . . . . . . . . . . . . . . . . . . . . . . . . 3 4.2. Clients . . . . . . . . . . . . . . . . . . . . . . . . . 4 5. Security Considerations . . . . . . . . . . . . . . . . . . . 4 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 4 7.1. Normative References . . . . . . . . . . . . . . . . . . 4 7.2. Informative References . . . . . . . . . . . . . . . . . 4 Appendix A. Change Log . . . . . . . . . . . . . . . . . . . . . 5 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 5 1. Introduction The DNS protocol [RFC1035] supports use of persistent TCP connections, although guidance as to when a connection should be terminated (and by which party) is limited [RFC5966]. This document updates the Extension Mechanisms for DNS (EDNS(0)) [RFC6891] by specifying a new single-bit flag in a DNS response that when seen in a packet carried over a connection-orientated transport protocol indicates to the client that it should close the current connection. Having the client close the connection reduces the amount of TCP state information that must be stored by the server compared to that resulting from the server initiating a unilateral close itself. TODO: does it make sense to specify a request side meaning for this flag, indicating that the server may half-close its "read" side of the connection? This would make the semantics even closer to those of the HTTP/1.1 "Connection: close" header (see Section 14.10 of [RFC2616]) 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 [RFC2119]. Bellis Expires April 27, 2015 [Page 2] Internet-Draft Connection Close Signalling for DNS October 2014 3. Specification The "Connection Close" (CC) bit is held in the third-most signifiant bit of the third byte of the "extended RCODE and flags" portion of an EDNS(0) OPT meta-RR: +0 (MSB) +1 (LSB) +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ 0: | EXTENDED-RCODE | VERSION | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ 2: |DO| Z|CC| Z | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ Note to RFC editor: replace the first 'Z' in the figure above with 'TO' if draft-hzhwm-dprive-start-tls-for-dns is published as an RFC before this specification. 4. Connection Handling 4.1. Servers Servers MAY set this flag to indicate that further queries received over the current connection should not be sent. An incompatible client will not understand this flag and may continue sending requests and therefore the server MUST NOT refuse to service subsequent requests. The server MAY unilaterally close idle connections regardless, per [RFC5966] and Section 4.2.2 of [RFC1035] Since this flag requires EDNS(0) support, note that this flag cannot be set unless the client has indicated support for EDNS(0) by sending an OPT meta-RR itself, per Section 7 of [RFC6891] TODO: note - the constraint in RFC 6891 appears unnecessarily strict - it appears to mandate that the EDNS(0) support indication is on a per-request basis, but it would be reasonable on a connection- orientated transport to assume that ANY preceding request on that connection with an OPT RR is sufficient to indicate that the client supports EDNS(0). TODO: if a request-side semantic is defined for this flag, what are the TCP state-maintenance implications if the server performs a 'shutdown(fd, SHUT_RD)'? Bellis Expires April 27, 2015 [Page 3] Internet-Draft Connection Close Signalling for DNS October 2014 4.2. Clients Clients receiving a packet with this flag set MUST NOT send any further queries over the current connection and MUST initiate closure of that connection. TODO: what are the TCP state-maintenance implications if the client performs a 'shutdown(fd, SHUT_WR)'? 5. Security Considerations None identified (yet). 6. IANA Considerations IANA are requested to update the EDNS Header Flag Registry according to Section 3. Note to IANA and RFC Editor: The actual bit assigned will depend on whether any other document specifies a used for the above-specificed bit in advance of publication of this document as an RFC. 7. References 7.1. Normative References [RFC1035] Mockapetris, P., "Domain names - implementation and specification", STD 13, RFC 1035, November 1987. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC5966] Bellis, R., "DNS Transport over TCP - Implementation Requirements", RFC 5966, August 2010. [RFC6891] Damas, J., Graff, M., and P. Vixie, "Extension Mechanisms for DNS (EDNS(0))", STD 75, RFC 6891, April 2013. 7.2. Informative References [RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H., Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999. Bellis Expires April 27, 2015 [Page 4] Internet-Draft Connection Close Signalling for DNS October 2014 Appendix A. Change Log Note to RFC editor: remove this section before publication. draft-bellis-dnsop-connection-close-00 Initial draft Author's Address Ray Bellis Nominet UK Minerva House Edmund Halley Road Oxford Science Park Oxford OX4 4DQ United Kingdom Phone: +44 1865 332211 Email: ray.bellis@nominet.org.uk URI: http://www.nominet.org.uk/ Bellis Expires April 27, 2015 [Page 5]