OPSAWG Working Group M. Richardson
Internet-Draft Sandelman Software Works
Intended status: Best Current Practice July 08, 2019
Expires: January 9, 2020

Operational Considerations for use of DNS in IoT devices


This document details concerns about how Internet of Things devices use IP addresses and DNS names. The issue becomes acute as network operators begin deploying RFC8520 Manufacturer Usage Description (MUD) definitions to control device access.

This document explains the problem through a series of examples of what can go wrong, and then provides some advice on how a device manufacturer can best make deal with these issues. The recommendations have an impact upon device and network protocol design.

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This Internet-Draft will expire on January 9, 2020.

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Table of Contents

1. Introduction

[RFC8520] provides a standardized way to describe how a specific purpose device makes use of Internet resources. Access Control Lists (ACLs) can be defined in an RFC8520 Manufacturer Usage Description (MUD) file that permit a device to access Internet resources by DNS name.

Use of a DNS name rather than IP address in the ACL has many advantages: not only does the layer of indirection permit the mapping of name to IP address to be changed over time, it also generalizes automatically to IPv4 and IPv6 addresses, as well as permitting loading balancing of traffic by many different common ways, including geography.

At the MUD policy enforcement point – the firewall – there is a problem. The firewall has only access to the layer-3 headers of the packet. This includes the source and destination IP address, and if not encrypted by IPsec, the destination UDP or TCP port number present in the transport header. The DNS name is not present!

In order to implement this, there must be a mapping between the names in the ACLs and layer-3 IP addresses. The first section of this document details a few strategies that are used.

The second section of this document details how common manufacturer anti-patterns get in the way this mapping.

The third section of this document details how current trends in DNS resolution such as public DNS servers, DNS over TLS (DoT), and DNS over HTTPS (DoH) cause problems for the strategies employed. Poor interactions with content-distribution networks is a frequent pathology that results.

The fourth section of this document makes a series of recommendations ("best current practices") for manufacturers on how to use DNS, and IP addresses with specific purpose IoT devices.

The Privacy Considerations section concerns itself with issues that DNS-over-TLS and DNS-over-HTTPS are frequently used to deal with. The question is how these concerns apply to IoT devices located within a residence or enterprise is dealt with.

The Security Considerations section covers some of the negative outcomes should MUD/firewall managers and IoT manufacturers choose not to cooperate.

2. Strategies to map names


3. DNS and IP Anti-Patterns for IoT device Manufacturers


4. DNS privacy and outsourcing vs MUD controllers


5. Recommendations on MUD and DNS co-existence


6. Privacy Considerations


7. Security Considerations


8. References

8.1. Normative References

[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.
[RFC8520] Lear, E., Droms, R. and D. Romascanu, "Manufacturer Usage Description Specification", RFC 8520, DOI 10.17487/RFC8520, March 2019.

8.2. Informative References

[RFC1034] Mockapetris, P., "Domain names - concepts and facilities", STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987.

Appendix A. Appendices

Author's Address

Michael Richardson Sandelman Software Works EMail: mcr+ietf@sandelman.ca