[Mud] iot-mud-dns operational considerations

[Michael Richardson <[e-mail]>]

I threw this together while waiting for the DT to process my other
submissions.  (It got rather slow...)
It's very drafty!

https://datatracker.ietf.org/doc/draft-richardson-opsawg-mud-iot-dns-considerations/

I'll just past the intro, which is all there really is!
I'll probably push this at ADD effort, after the BOF is better understood.


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.

--
Michael Richardson <[e-mail]>, Sandelman Software Works
 -= IPv6 IoT consulting =-