Early Review of draft-ietf-opsawg-mud-08

Request Review of draft-ietf-opsawg-mud-08
Requested rev. 08 (document currently at 20)
Type Early Review
Team General Area Review Team (Gen-ART) (genart)
Deadline 2017-08-29
Requested 2017-08-15
Requested by Joe Clarke
Other Reviews Secdir Early review of -08 by Adam Montville (diff)
Iotdir Early review of -08 by Henk Birkholz (diff)
Yangdoctors Early review of -08 by Martin Bjorklund (diff)
Rtgdir Last Call review of -13 by Adrian Farrel (diff)
Secdir Last Call review of -13 by Adam Montville (diff)
Genart Telechat review of -20 by Robert Sparks
Opsdir Telechat review of -20 by Scott Bradner
The opsawg working group feels this document is generally in good shape, and the work has been progressing nicely.  The document is very readable, and it would benefit from an early review especially around areas of security and IoT.  By MUD's very nature, it relies on trust and needs to be friendly to constrained, purpose-built devices.

The YANG modules defined within have been previously reviewed, but could use a new set of YANG Doctor eyes.  In particular, comments have been raised about what leafs should be mandatory (if any).

Thank you.
Review State Completed
Reviewer Robert Sparks
Review review-ietf-opsawg-mud-08-genart-early-sparks-2017-08-30
Posted at https://mailarchive.ietf.org/arch/msg/gen-art/xC0DGox-RFN-kFntamwDJTE_lsI
Reviewed rev. 08 (document currently at 20)
Review result Almost Ready
Draft last updated 2017-08-30
Review completed: 2017-08-30


This is an exciting concept, and the draft overall is approachable. I
have identified a few areas I think need more detail, and have a 
longish list of nits (please don't take that to be negative).


I find the structure of the introduction unclear. Please consider
reworking it.  I would suggest even more succinctly listing goals and
constraints, and then intended applicability (these things are in the
current text, but I think you can render them much more efficiently). In
particular, the argument that implementers of things are incented only to
provide the minimal amount of behavior to get their thingyness could be
more strongly highlighted.

The document proposes "reputation services". It needs more words about
whether those exist, and what scopes the architecture imagines (an
enterprise might have a different idea of a reputation service than a
residence). There is a notion of "decent web reputations" in the security
considerations section. Who determines that? The security considerations
section should talk about attacks against the reputation services.

In the first paragraph of Section 2, it's not clear if you are trying
to restrict the models to only those in the two documents in the list
following the paragraph. 

I am not a YANG doctor, so this may be in the weeds, but it feels like
there's a discrepancy between the diagram at the end of section 2 and the
element definitions in section 3. In particular 3.7 doesn't seem to align
with what the diagram or the example in Appendix B uses. Should you be 
defining "from-device-policy" and "to-device-policy" instead of
"packet-direction"? (I'm wondering if 3.7 reflects an older design?)

At section 3.13, the description of my-controller is not quite right.
This bit signals to the mud controller to use a mapping that it knows
about or creates. Something else established that class (and maybe gave
it a name). I talked about this with Eliot and he has a better 
description to use.

It's not clear to me that this is a good use of .well-known. I suggest
getting an expert review on the proposed usage. (I had a quick 
conversation with Mark Nottingham and got some initial feedback that 
I'm passing along here. I'm sure there's more that an in-depth review
would identify.) Why wouldn't a URI template (RFC6570) do the job? 
Rather than use RFC3986's query, consider pointing to HTML5 (which
would bring the more familiar key=value format). 

The document needs to say more about how HTTP is used. I assume you only
intend to use GET, and that you expect redirects to be followed, and that
nothing special needs to be considered with caching? The document needs
to be explicit about it. Take a look at 
<https://mnot.github.io/I-D/bcp56bis/>. (There's been some conversation
about it on the art list, so Eliot, at least, is already aware of it - 
see <https://mailarchive.ietf.org/arch/search/?q=bcp56bis>)

I think there needs to be more discussion of the PKI used for signing MUD

Consider discussing whether the stacks used by typical things will let
them add DHCP options (or include bits in the other protocols being 
enabled). If it's well known (I can't say) that these stacks typically
_won't_ provide that functionality, then you should punch up the
discussion of the controllers mapping other identifiers to MUD URLs on
behalf of the thing.

You suggest the DHCP Client (which is a thing) SHOULD log or report 
improper acknowledgments from servers. That's asking a bit much from
a thing. I suspect the requirement is unrealistic and should be removed
or rewritten to acknowledge that things typically won't do that.

The security and deployment considerations sections talk about what the
need for coordination if control over the domain name used in the URL
changes. It should talk more about what happens if the new administration
of the domain is not interested in facilitating a transition (consider
the case of a young company with a few thousand start-up-ish things out
there that loses a suit over its name). Please discuss whether or not
suddenly losing the MUD assisted network configuration is expected to
leave the devices effectively cut-off. 

Right now, you leave the DHCP server (when it's used) responsible for
clearing state in the MUD controller. Please discuss what happens when
those are distinct elements (as you have in the end of section 9.2) and
the DHCP server reboots. Perhaps it would make sense for the DHCP server
to hand the length of the lease it has granted to the MUD controller and
let the MUD controller clean up on its own?

The document currently suggests that a piece of software inspect the
WHOIS database to see if registration ownership of a domain has changed.
Do you really mean software, or should this be advice to the
administrator of the controller instead? 


I recommend an editorial pass focusing on simplifying sentences. Look
particularly where the word "therefore" is used and consider
restructuring the surrounds. (It is used non-sequitur in a couple of
places). Be careful to call out actors explicitly (I note the places 
that particularly caught my eye below).

Some specific nits:

The abstract speaks only about properties of MUD but does not describe
what MUD _is_, or is good for. A few more words here would help.

Next to last paragraph of section 1 (before 1.1): A means for _who_ to
retrieve the description? (Consider rendering the three list elements on
their own lines.)

The last sentence of section 1 treats "enterprise networks" more
specially than it intends, I think. Why couldn't _any_ network do this?
Could the sentence be reworded to make it clear that enterprise networks
are an example?

First sentence of 1.1: Perhaps you mean "general purpose computing
devices" instead of "general computing"? "their" has an unclear

Last paragraph of 1.3: It's unclear what "such an approach" is intended
to point to. Would "a general solution that required capabilities their
particular device would not use" make more sense?

First paragraph of 1.5: "might to allow" is probably meant to be "might
be to allow". What does it mean for a controller to "need to speak COAP".
Do you mean "controllers capable of speaking COAP"?

Fourth paragraph of 1.5 at the discussion of time and effort: Consider
rephrasing this to focus on the result of the time and effort (high
quality) rather than the time and effort itself.

In the list of abstractions at the end of 1.5, you have three things you
describe as devices and one thing you describe as a class. You later talk
about the abstractions you've described as devices as classes. At this
point in the document what you mean by "class" has not been made as
explicit as it could be.

Section 1.8, item 3: the MUD file doesn't have hosts in it (it has
identifiers of some kind). Consider being more explicit about what
you mean by testing that against a reputation service.

Section 3.1: You say "Which turn was taken". I think you meant
"Which, in turn, was taken". Consider deleting "for those keeping score".

Section 3.3 is missing a word at "the location any MASA service"?

I found the prose in the descriptions of the "manufacturer" and
"same-manufacturer" elements (3.8 and 3.9) very confusing. I think
additional prose introducing the concepts and maybe some examples would
be very useful.

What do you mean by "matches" at 3.10. Do you mean "is"?

The caution in the 2nd paragraph of 3.12 is not clear.

At section 4, consider pointing out that you are not allowing 
DHCP by default, and that devices that are expected to use DHCP
need to have an explicit allow in their MUD file. 

The description of the manufacturer leaf in the MUD YANG model
could be made more useful.

Provide a reference for "giaddr" when you use it in section 9.2.

Section 14, 2nd paragraph: additional segmentation of what?

Second paragraph of Section 15 - it would help to be more precise
with agency. _Who_ should review the class?

In the security considerations section, when you get to the "if for some
reason it is not possible to determine whether ownership has changed",
_who_ are you suggesting conduct further review?