Re: [rtcweb] OPS-Dir review of draft-ietf-rtcweb-stun-consent-freshness-13

[joel jaeggli <[e-mail]>]

Thanks David,

I'll be looking with interest for the addressing of items 1/2.

joel

On 5/14/15 4:21 PM, Black, David wrote:
> I have reviewed this document as part of the Operational directorate's
> ongoing effort to review all IETF documents being processed by the IESG.
> These comments were written with the intent of improving the operational
> aspects of the IETF drafts. Comments that are not addressed in last call
> may be included in AD reviews during the IESG review.  Document editors
> and WG chairs should treat these comments just like any other last call
> comments.
> 
> Document: draft-ietf-rtcweb-stun-consent-freshness-13
> Reviewer: David Black
> Review Date: May 14, 2015
> IETF LC End Date: May 15, 2015 (on -11)
> 
> Summary: This draft is on the right track, but has open issues
>  		described in the review.
> 
> This draft describes use of STUN to obtain ongoing consent to send in
> a fashion that is secured by the use of cryptographically strong nonces
> as STUN transaction IDs.
> 
> -- Major issues --
> 
> [1] The draft seems to be missing discussion of applicability - what
> environments and/or protocols is this mechanism intended for or applicable
> to?  Is this generally applicable wherever ICE and STUN are used?  I don't
> see any RFCs listed as updated by this draft, so I'm guessing that this
> is not intended to promulgate new requirements for all uses of ICE and
> STUN, but this should be clarified.  The shepherd writeup implies that
> this draft is intended primarily for WebRTC.
> 
> [2] The security considerations appear to be incomplete.
> There should be an explanation of why cryptographically strong STUN
> transaction IDs are required (e.g., there are no cryptographically
> strong IDs in the TCP consent mechanism noted on p.4), and there should
> be a discussion of how and why replays of previous consent responses
> are harmless (will be ignored by the recipient).  The mechanism design
> appears to be ok, but this rationale should be provided in terms of
> attacks that are of concern and how they are prevented - a primary
> intent appears to be to resisting off-path attacks.
> 
> -- Minor Issues --
> 
> [3] In Section 1, please explain what ICE-lite is.  A suitable reference
> should suffice.
> 
> [4] In Section 4.1, please explain or provide a reference for what "paced"
> means in "paced STUN connectivity checks or responses."
> 
> -- Nits/Editorial Comments --
> 
> The SRTP paragraph in Section 8 (Security Considerations) feels out of place
> - this looks like design rationale material that would be better located in
> Section 3.
> 
> idnits 2.13.02 found an unused reference:
> 
>   == Unused Reference: 'I-D.ietf-rtcweb-overview' is defined on line 320, but
>      no explicit reference was found in the text
> 
> That reference is likely to be useful to address the absence of discussion of
> applicability (major issue [1], above).
> 
> --- Selected RFC 5706 Appendix A Q&A for OPS-Dir review ---
> 
> This mechanism is an incremental modification to the STUN and ICE protocols,
> and can be implemented by one party to a communication session; ordinary
> response generation behavior (already required) reflects the cryptographically
> strong STUN transaction IDs on which the mechanism is based.  As a result, the
> mechanism can be deployed at one end of a two-party communication session
> without impact on the other party.  This is implied by section 3 of the draft,
> but would be useful to state explicitly.  [A.1.1 - deployment]
> 
> The mechanism has been defined to limit the amount of added traffic and to
> shut down unwanted traffic, plus contains a facility to desynchronize
> independent users of this protocol.  Some rationale should be added for
> the choice of the 30 second timeout period.  [A.1.5 - network impact]
> 
> There is an obvious fault condition, namely that consent is lost or revoked
> causing immediate cessation of traffic.  While the details depend on the
> environment in which this mechanism is used, it'd be helpful to add a sentence
> or two on reporting of the state of STUN consent-based connectivity and how
> that reporting should or may relate to reporting of the state of other forms
> of connectivity (e.g., TCP, SRTP/SRTCP) that are mentioned in this draft.
> [A.1.8 - fault and threshold conditions]
> 
> This mechanism is a simple extension to existing protocols, and should fit
> into existing configuration and management for those protocols. [A.1.9 -
> configuration, A.2 - Management (in general)]
> 
> It might be useful to mention the utility of tracking frequency and duration
> of loss and re-establishment of consent-based connectivity, as such information
> has operational value.  In particular, a discussion of how a server could infer
> loss of connectivity with a client that is using this mechanism might be useful
> to add, as the operational concerns may be more significant for servers and
> related networks than clients. [A.2.2 - management information, A.2.3 - fault
> management].
> 
> The primary operational impact of this protocol should be reduction in unwanted
> traffic, which is a benefit - the consent check traffic added by this protocol
> should not have significant impacts.  The writeup indicates that implementers
> have reviewed the draft and implementations are in progress. [A.3 - Documentation]
> 
> Thanks,
> --David
> ----------------------------------------------------
> David L. Black, Distinguished Engineer
> EMC Corporation, 176 South St., Hopkinton, MA  01748
> [phone]             FAX: [phone]
> [e-mail]        Mobile: [phone]
> ----------------------------------------------------
> 
> 
>