Re: [Gen-art] Genart telechat review of draft-ietf-opsawg-mud-20

Eliot Lear <> Tue, 10 April 2018 10:43 UTC

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To: Robert Sparks <>,
References: <>
From: Eliot Lear <>
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Subject: Re: [Gen-art] Genart telechat review of draft-ietf-opsawg-mud-20
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Hi Robert and thanks again for the review.  Please see below for
responses.  These are my personal views.  The WG chairs / shepherds may
have different opinions.

On 09.04.18 19:57, Robert Sparks wrote:
> Reviewer: Robert Sparks
> Review result: Ready with Issues
> I am the assigned Gen-ART reviewer for this draft. The General Area
> Review Team (Gen-ART) reviews all IETF documents being processed
> by the IESG for the IETF Chair. Please wait for direction from your
> document shepherd or AD before posting a new version of the draft.
> For more information, please see the FAQ at
> <>;.
> Document: draft-ietf-opsawg-mud-20
> Reviewer: Robert Sparks
> Review Date: 2018-04-09
> IETF LC End Date: 2017-11-07
> IESG Telechat date: 2018-04-19
> Summary: Almost ready but with minor issues to address before publication as a
> standards track RFC 
> Minor issues:
> Section 3.15 is confused, and I don't think you'll get the implementation you
> intend with the MUST in the current language. direction-indicated is not a
> flag. The text about dropping should talk about matching the direction that was
> indicated.

Having reread this section (and perhaps I am a bit too close to the
text), perhaps it is a bit confused.  How about something along the
following lines:

3.15.  direction-initiated

   When applied this matches the direction in which a TCP connection is
   initiated.  When direction initiated is "from-device", packets that are
   transmitted in the direction of a thing MUST be dropped unless the thing
   has first initiated a TCP connection.  This node may be implemented in
   its simplest form by looking at naked SYN bits, but may also be
   through more stateful mechanisms.
  [RFC6092] specifies IPv6 guidance best
   practices.  While that document is scoped specifically to IPv6, its
   contents are applicable for IPv4 as well. 


> The quoted issues below are from my early review of -08. I don't think they've
> been addressed or responded to. Apologies if I missed a response.
>> 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.
>> I think there needs to be more discussion of the PKI used for signing MUD
>> files.

While this section is admittedly a bit vague, we need some operational
experience to develop the appropriate use of PKI as an anchor for
reputations.  This having been said, if you have a specific proposal for
text, I'd be interested in what you have to say.

>> 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.

We did indeed add some text about this, almost verbatim to what you have
above (I think at your suggestion).  This can be found in the
introduction toward the bottom of page 9.

>> 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.

I propose to delete that paragraph to match that we do not wish DHCP
servers to modify their state.  This would address your concern (also
see below).

>> 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. 

The example you are talking about is a subset of what happens if the
file simply doesn't exist.  At worst, one is left in a situation no
worse than we are today: that is, someone will have to manually decide
policy, or apply a default policy.  This particular text is the subject
of separate piece of work that Thorsten Dahm and Steve Rich are
considering, and it is also the subject of some ongoing research.  That
is to say: we might be able to do better in the future when we have some
operational experience.

>> 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?

Ok, two issues:

 1. There was some text that should have been removed, referring to the
    DHCP server returning the MUD-URL as part of state.  With everyone's
    permission, I propose to remove that text.  No additional DHCP
    server state should be required to implement this option.
 2. I agree that we could be a bit more descriptive about what would
    happen if a reboot of the DHCP server.  I also like your idea about
    mentioning the lease time to the MUD controller.  With that in mind,
    how about the following text:

With that in mind, I propose the following edit:

DHCP servers may implement MUD functionality themselves or they may
pass along appropriate information to a network management system or
MUD controller.  A DHCP server that does process the MUD URL MUST adhere
to the process specified in {{RFC2818}} and {{RFC5280}} to validate
the TLS certificate of the web server hosting the MUD file.  Those
servers will retrieve the file, process it, create and install the
necessary configuration on the relevant network element.  Servers
SHOULD monitor the gateway for state changes on a given interface.  A
DHCP server that does not provide MUD functionality and has forwarded
a MUD URL to a MUD controller MUST notify the MUD controller
of any corresponding change to the DHCP state of the client
(such as expiration or explicit release of a network address lease).

Should the DHCP server fail, in the case when it implements the MUD
controller functionality, any backup mechanisms SHOULD include the MUD
state, and the server SHOULD resolve the status of clients upon its
restart, similar to what it would do, absent MUD controller
functionality.  In the case where the DHCP server forwards information
to the MUD controller, the MUD controller will either make use of
redundant DHCP servers for information, or otherwise clear state based
on other network information, such as monitoring port status on a
switch via SNMP, Radius accounting, or similar mechanisms.

> Nits:
> There is tension between the paragraph in the introduction that characterizes
> the manufacturer as the entity that provides the mud file and the third bullet
> in the intent list about speeding vulnerability resolution for devices that
> are no longer supported by the manufacturer (you intend here that someone other
> than the original manufacturer or integrator is providing a new mud file).

Perhaps this is best fixed by dropping the phrase "by the manufacturer"?

> Instead of "A light bulb is intended to light a room.", I suggest 
> "A light bulb is intended to light a given space." (There are lightbulbs
> meant for outdoor use, and others for only inside cabinets or appliances.)


> Instead of "We make use of YANG because of the time and effort spent to develop
> accurate..." I suggest "We make use of YANG because it provides accurate..."

> At the end of section 1.7, instead of "For these reasons only a limited subset
> YANG-based configuration is permitted in a MUD file.", I suggest "For these
> reasons, the YANG-based configuration in a MUD file is limited to the YANG
> modules defined in this document." or something similar.
s/defined/specified/ but otherwise ok.

> In section 3.6, the parenthesized clause does not belong in the sentence in 
> which it currently appears. I suggest it belongs somewhere in the previous
> sentence.

I've removed it and rewritten as follows:

The intent is for administrators to be able to see a
brief displayable description of the Thing.

> In section 3.13 you talk about classes that are standardized. Where does 
> someone find out about standardized classes?

They're described in the document
> Micro-nits:
> "Our work begins with" in section 1.5 is awkward and I suspect will cause
> problems if this document is translated into other languages.

If you *know* this to be a problem, I will make a change.

> At "======= The MUD URL identifies" in section 5, I suggest deleting the =
> signs.

I believe this is corrected.
> Please provide a reference or better description for "so-called east-west
> infection""

I'll change this to "lateral infection (infection of devices that reside
near one another)".
> The string "enorcement" appears a couple of times in the models. It is intended
> to be "enforcement".
Thanks for catching these.