DNS Extensions (DNSEXT) A. Hubert
Internet-Draft Netherlabs Computer Consulting BV.
Intended status: Standards Track D. Ulevitch
Expires: October 22, 2009 EveryDNS
April 20, 2009
EDNS Option for performing a data PING
draft-hubert-ulevitch-edns-ping-01.txt
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Abstract
For various reasons, it may be desirable to ask a remote nameserver
to add certain data to the response to a query.
This document describes an EDNS option that implements such
behavioiur.
Table of Contents
1. Key words . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Protocol . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.1. Nameserver Behaviour . . . . . . . . . . . . . . . . . . . 5
3.2. Resolver Behaviour . . . . . . . . . . . . . . . . . . . . 5
3.3. The PING option . . . . . . . . . . . . . . . . . . . . . 5
3.4. Presentation format . . . . . . . . . . . . . . . . . . . 5
4. Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . 6
4.1. Truncation . . . . . . . . . . . . . . . . . . . . . . . . 6
5. Possible Uses and Implementation Guidance . . . . . . . . . . 7
6. Security Considerations . . . . . . . . . . . . . . . . . . . 8
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 10
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11
9.1. Normative References . . . . . . . . . . . . . . . . . . . 11
9.2. Informative References . . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12
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1. Key words
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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2. Introduction
This document describes an EDNS option that can be used to ask a
remote nameserver, be it authoritative or a caching resolver, to copy
an opaque string from the query to the response.
This string can be used to verify proper transmission of DNS
questions and responses of various sizes.
Additionally, implementations could utilise EDNS PING as a way to
enhance the security of DNS over UDP.
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3. Protocol
This document uses an EDNS [RFC2671] option to signal that the remote
nameserver must copy this option, and its payload, from the query to
the response, without truncation or modification.
3.1. Nameserver Behaviour
A name server that understands the PING option and chooses to honor a
particular PING request MUST respond by including the opaque payload
in a PING option in an EDNS OPT pseudo-RR in the response message.
The PING response should be included in addition to the records that
would be returned if no PING request were included.
An oversized payload MUST be ignored.
3.2. Resolver Behaviour
Resolvers, including stub resolvers, can signal their desire for an
EDNS PING response by adding a PING option in an EDNS OPT pseudo-RR
in the question message.
The resolver is free to choose a length for the opaque payload of the
PING option request, but care should be taken not to exceed
acceptable DNS packet size limits.
Malformed or truncated responses should be treated as suspicicous.
Empty responses, however, may simply indicate a response from a
nameserver which does not support EDNS PING responses.
3.3. The PING option
The OPTION-CODE for the PING option is 5.
The OPTION-DATA for the PING option is an opaque byte string, the
semantics of which are deliberately left outside of this document.
The minimum length of the OPTION-DATA is 4 bytes, the maximum length
is 16 bytes.
3.4. Presentation format
The presentation format of the PING option is left outside the scope
of the protocol. It should be observed that the payload of the PING
option is completely arbitrary, and need not be null-terminated, and
in general will not be.
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4. Discussion
The PING option is modeled on ICMP ECHO-REQUEST and ECHO-RESPONSE
packets ([RFC0792]), and can in fact be used in a similar manner to
verify connectivity.
An example of such verification is to determine the maximum response
size that arrives unscathed.
In addition, a resolver is free to append a PING option to outgoing
queries in order to protect itself from accepting false data by
requesting a more clearly marked response. Such a PING-adorned
response can clearly be separated from responses sent by third
parties.
4.1. Truncation
In some cases, adding the PING option to a response message may
trigger message truncation. This specification does not change the
rules for DNS message truncation in any way, but implementers will
need to pay attention to this issue.
Implementations claiming conformance to this draft, and which are
configured to honor PING requests MUST respond to such requests, and
must not drop the PING response to prevent truncation.
By definition, a resolver that requests PING responses also supports
EDNS, so a resolver that requests PING responses can also use the
"sender's UDP payload size" field of the OPT pseudo-RR to signal a
receive buffer size large enough to make truncation unlikely.
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5. Possible Uses and Implementation Guidance
While this document standardizes how the EDNS PING option can be
used, it does not specify how or when it should be used.
In this non-normative section, guidance is given how this option
might best be used to achieve certain effects. It is expected that
this guidance will be supplanted by the experience of implementors
over time.
In case the EDNS-PING option is used to protect against the spoofing
of DNS answers, care must be taken that the payload of the EDNS-PING
is sufficiently long and sufficiently unpredictable to serve this
purpose.
Proper unpredictability can be achieved by employing a high quality
(pseudo-)random generator, as described in [RFC4086].
Not all servers support EDNS Options, nor do all servers respond well
to EDNS queries per se. Like EDNS in general, care must be taken to
determine if a nameserver responds well to EDNS-PING adorned queries.
If the state of a remote server's support for EDNS-PING is cached,
and EDNS-PING is used to protect against spoofing, it is imperative
that such state can not be downgraded within a reasonable timeframe.
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6. Security Considerations
While EDNS PING might be used to enhance the security of query/
response correlation, in and of itself it is not expected to have
security implications.
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7. IANA Considerations
IANA is expected and requested to reserve option 5 for EDNS PING.
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8. Acknowledgments
Donald Eastlake first discussed the concept of DNS cookies
([I-D.eastlake-dnsext-cookies]), which are remarkably similar to EDNS
PING requests, but cover a wider scope and have a defined purpose.
Most of this document was copied almost verbatim from [RFC5001] which
implements a very similar EDNS option, used for very different
purposes. Thanks are due to Rob Austein and other contributors to
the NSID RFC.
Although any mistakes remain our own, the authors gratefully
acknowledge the help and contributions of:
Peter van Dijk,
Aki Tuomi
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9. References
9.1. Normative References
[RFC0792] Postel, J., "Internet Control Message Protocol", STD 5,
RFC 792, September 1981.
[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.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2181] Elz, R. and R. Bush, "Clarifications to the DNS
Specification", RFC 2181, July 1997.
[RFC2671] Vixie, P., "Extension Mechanisms for DNS (EDNS0)",
RFC 2671, August 1999.
9.2. Informative References
[I-D.eastlake-dnsext-cookies]
3rd, D., "Domain Name System (DNS) Cookies",
draft-eastlake-dnsext-cookies-03 (work in progress),
February 2008.
[RFC1123] Braden, R., "Requirements for Internet Hosts - Application
and Support", STD 3, RFC 1123, October 1989.
[RFC4086] Eastlake, D., Schiller, J., and S. Crocker, "Randomness
Requirements for Security", BCP 106, RFC 4086, June 2005.
[RFC5001] Austein, R., "DNS Name Server Identifier (NSID) Option",
RFC 5001, August 2007.
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Authors' Addresses
Bert Hubert
Netherlabs Computer Consulting BV.
Braillelaan 10
Rijswijk (ZH) 2289 CM
The Netherlands
Email: bert.hubert@netherlabs.nl
David Ulevitch
EveryDNS
2601 Greenwich, #4
San Francisco, CA 94123
United States of America
Email: davidu@everydns.net
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