Re: [secdir] [rmcat] Secdir last call review of draft-ietf-rmcat-nada-11

Colin Perkins <> Fri, 16 August 2019 14:54 UTC

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From: Colin Perkins <>
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Date: Fri, 16 Aug 2019 15:54:07 +0100
Cc: Gorry Fairhurst <>, Sean Turner <>,,,, IETF <>
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To: Mirja Kuehlewind <>
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Subject: Re: [secdir] [rmcat] Secdir last call review of draft-ietf-rmcat-nada-11
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> On 16 Aug 2019, at 13:59, Mirja Kuehlewind <> wrote:
> Hi Sean, hi Gorry,
> Thanks for your review and feedback. Please see below.
>> On 13. Aug 2019, at 09:56, Gorry Fairhurst <> wrote:
>> See  below:
>> On 13/08/2019, 02:08, Sean Turner via Datatracker wrote:
>>> Reviewer: Sean Turner
>>> Review result: Has Nits
>>> Hi! I'm no congestion control expert so nothing in the main body jumped out at
>>> me.  I did take a little time to review some security considerations for other
>>> congestion control RFCs and just wanted to make sure the same kind of
>>> information is getting addressed.  I indicated the result of this review as
>>> "has nits" because there is a pretty good chance I am just suggesting some
>>> editorial tweaks.
>>> The security considerations rightly points out that this mechanism is
>>> susceptible to the same kind of attacks as TCP (e.g., hijack, replacement) and
>>> what mitigations to use (i.e., integrity protection of the RTCP feedback
>>> messages).  But, what is missing is what happens if these attacks succeed: DoS
>>> or in the worst case congestion collapse?  So, maybe instead of:
>>>   As such, it is vulnerable to attacks where feedback
>>>   messages are hijacked, replaces, or intentionally injected with
>>>   misleading information, similar to those that can affect TCP.
>>> Maybe:
>>>   As such, it is vulnerable to attacks where feedback
>>>   messages are hijacked, replaces, or intentionally injected with
>>>   misleading information resulting in denial of service, similar
>>>   to those that can affect TCP.
>>> Also, unless I've completely misread this paragraph it seems like you are
>>> talking about two things: 1) it's just like TCP, and 2) "The modification of
>>> sending rate ...".  So, maybe split the paragraph along those lines.
> I think this is actually based on text that we used for scream (now RFC8298) which is another congestion control developed in rmcat. I think we refined that text also based on a SEC (or GEN?) review comment at that time and people were at the end satisfied with it. However, your proposed change above could surely be integrated and I leave it to the authors if they want to refine the text further. 
>>> Further questions:
>>> 1. Are there any concerns related to a greedy receiver who wants to gobble up
>>> more than its fair share of network bandwidth?
> This is a very general point for all congestion control schemes, and for rmcat it is also discussed in draft-ietf-rmcat-cc-requirements (which is sitting in the RFC editor queue for a while as part of the 238 cluster…). I personally don’t see too much value in discussing this here once again (given the generic nature of the problem and very unclear definition of “fair”).
>>> 2. Seems like maybe you also need to refer to the RTP/RTCP security
>>> considerations because it seems like security primarily needs to be considered
>>> in the context of a specific transport protocol and its authentication
>>> mechanisms.
> Hm, also not sure here because, while this congestion control scheme is developed for RTP/RTCP, it's defined in a more generic way and there are actually no real dependencies on a specific protocol.

For both this and the GenART review, it should maybe point to draft-ietf-avtcore-cc-feedback-message-04 as an example mechanism to carry congestion feedback. The security considerations in that draft highlight some of these issues, and point to the RTP security mechanisms needed to secure the feedback.


>>> Cheers,
>>> spt
>> I also think that text (or similar) would also be valuable in the security considerations section.
> Gorry: Can you further explain what part this comment related to?
> Thanks!
> Mirja
>> Gorry

Colin Perkins