Internet DRAFT - draft-bellis-dnsop-connection-close
draft-bellis-dnsop-connection-close
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
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This Internet-Draft will expire on April 27, 2015.
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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].
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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)'?
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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.
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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/
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