Internet DRAFT - draft-lenders-dns-cns
draft-lenders-dns-cns
TBD M. S. Lenders
Internet-Draft FU Berlin
Intended status: Best Current Practice T. C. Schmidt
Expires: 27 April 2023 HAW Hamburg
M. Wählisch
FU Berlin
24 October 2022
Guidance on DNS Message Composition in Constrained Networks
draft-lenders-dns-cns-00
Abstract
This document provides guidance on the composition of DNS messages in
constrained networks, where the link layer may restrict payload sizes
significantly and batteries challenge power consumption.
About This Document
This note is to be removed before publishing as an RFC.
The latest revision of this draft can be found at https://anr-bmbf-
pivot.github.io/draft-lenders-dns-cns/draft-lenders-dns-cns.html.
Status information for this document may be found at
https://datatracker.ietf.org/doc/draft-lenders-dns-cns/.
Discussion of this document takes place on the TBD Working Group
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Source for this draft and an issue tracker can be found at
https://github.com/anr-bmbf-pivot/draft-lenders-dns-cns.
Status of This Memo
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This Internet-Draft will expire on 27 April 2023.
Copyright Notice
Copyright (c) 2022 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 (https://trustee.ietf.org/
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Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Constrained Resolver Considerations . . . . . . . . . . . . . 3
4. DNS Server Consideration . . . . . . . . . . . . . . . . . . 3
5. Security Considerations . . . . . . . . . . . . . . . . . . . 4
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 4
7.1. Normative References . . . . . . . . . . . . . . . . . . 4
7.2. Informative References . . . . . . . . . . . . . . . . . 4
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 5
1. Introduction
Many IoT scenarios rely on constrained nodes [RFC7228] and need the
Domain Name System (DNS). Constrained nodes [RFC7228], however,
challenge DNS resolution for two reasons. First, IoT networks, such
as IEEE 802.15.4 and LoRaWAN, often limit the payload of the data
link layer significantly in terms of size, which prevents common
(larger) DNS responses. Second, constrained nodes are often battery
powered and follow a strict duty cycle, which would benefit from
minimal number of DNS messages to reduce unnecessary device wake-ups.
Adoption layers such as 6LoWPAN [RFC4944] and SCHC [RFC8724] provide
fragmentation and compression to overcome the problem, but do not
help in principle. Fragmentation requires more buffer space to
account for lost fragments in lossy networks, and compression
introduces additional processing overhead.
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This document provides best common practices on DNS behavior, to
reduce fragmentation and power consumption in constrained networks
when IoT nodes resolve names.
2. Terminology
A "DNS server" is a server that provides DNS information to a
querying DNS client. For the purpose of this document, server and
client may communicate based on any DNS transport, not just DNS over
UDP [RFC1035], but also DNS over TLS [RFC7858], DNS over HTTPS
[RFC8484], or DNS over CoAP [I-D.ietf-core-dns-over-coap].
The terms "constrained node" and "constrained network" are used as
defined in [RFC7228].
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
3. Constrained Resolver Considerations
Nodes within a constrained network that implement DNS are assumed to
be stub resolvers [RFC8499]. This means they only query information
from a recursive DNS resolver and they MUST NOT distribute any DNS
information received from an upstream DNS server.
4. DNS Server Consideration
A DNS server that is aware that the querying node is a node within a
constrained network SHOULD resolve a CNAME or PTR record until the
resource record type originally requested by the node is reached.
This reduces the number of message exchanges within a constrained
network.
The DNS server SHOULD send compact answers, i.e., omit additional or
authority sections in a DNS reply. Additional and authority sections
should only be included if they help a DNS client to reduce queries.
One such example is DNS-SD [RFC6763], where the answer does not only
need to include an SRV record but also TXT and A/AAAA records to make
decent use of the reply.
TBD: Provide more specific example use case? Should the list be
almost complete?
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5. Security Considerations
In the case when DNS clients act as DNS servers, resolving CNAME and
PTR records at the upstream DNS server may lead to incorrect DNS
information forwarded by the client. As such, this document
prohibits the distribution of such information in Section 3
TODO more security
6. IANA Considerations
This document has no IANA actions.
7. References
7.1. Normative References
[RFC1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,
November 1987, <https://www.rfc-editor.org/rfc/rfc1035>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/rfc/rfc2119>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/rfc/rfc8174>.
7.2. Informative References
[I-D.ietf-core-dns-over-coap]
Lenders, M. S., Amsüss, C., Gündoğan, C., Schmidt, T. C.,
and M. Wählisch, "DNS over CoAP (DoC)", Work in Progress,
Internet-Draft, draft-ietf-core-dns-over-coap-00, 5
September 2022, <https://datatracker.ietf.org/doc/html/
draft-ietf-core-dns-over-coap-00>.
[RFC4944] Montenegro, G., Kushalnagar, N., Hui, J., and D. Culler,
"Transmission of IPv6 Packets over IEEE 802.15.4
Networks", RFC 4944, DOI 10.17487/RFC4944, September 2007,
<https://www.rfc-editor.org/rfc/rfc4944>.
[RFC6763] Cheshire, S. and M. Krochmal, "DNS-Based Service
Discovery", RFC 6763, DOI 10.17487/RFC6763, February 2013,
<https://www.rfc-editor.org/rfc/rfc6763>.
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[RFC7228] Bormann, C., Ersue, M., and A. Keranen, "Terminology for
Constrained-Node Networks", RFC 7228,
DOI 10.17487/RFC7228, May 2014,
<https://www.rfc-editor.org/rfc/rfc7228>.
[RFC7858] Hu, Z., Zhu, L., Heidemann, J., Mankin, A., Wessels, D.,
and P. Hoffman, "Specification for DNS over Transport
Layer Security (TLS)", RFC 7858, DOI 10.17487/RFC7858, May
2016, <https://www.rfc-editor.org/rfc/rfc7858>.
[RFC8484] Hoffman, P. and P. McManus, "DNS Queries over HTTPS
(DoH)", RFC 8484, DOI 10.17487/RFC8484, October 2018,
<https://www.rfc-editor.org/rfc/rfc8484>.
[RFC8499] Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS
Terminology", BCP 219, RFC 8499, DOI 10.17487/RFC8499,
January 2019, <https://www.rfc-editor.org/rfc/rfc8499>.
[RFC8724] Minaburo, A., Toutain, L., Gomez, C., Barthel, D., and JC.
Zuniga, "SCHC: Generic Framework for Static Context Header
Compression and Fragmentation", RFC 8724,
DOI 10.17487/RFC8724, April 2020,
<https://www.rfc-editor.org/rfc/rfc8724>.
Acknowledgments
TODO acknowledge.
* Carsten Bormann
* Ben Schwartz
Authors' Addresses
Martine Sophie Lenders
Freie Universität Berlin
Email: m.lenders@fu-berlin.de
Thomas C. Schmidt
HAW Hamburg
Email: t.schmidt@haw-hamburg.de
Matthias Wählisch
Freie Universität Berlin
Email: m.waehlisch@fu-berlin.de
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