Re: [Anima-signaling] draft-ietf-anima-grasp-08: DULL comments discovery be performed over TCP?)

Brian E Carpenter <brian.e.carpenter@gmail.com> Fri, 04 November 2016 04:21 UTC

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To: Toerless Eckert <tte+ietf@cs.fau.de>, draft-ietf-anima-grasp@ietf.org, anima-signaling@ietf.org
References: <20161031221855.GA1970@faui40p.informatik.uni-erlangen.de> <18011.1478097279@obiwan.sandelman.ca> <20161103221054.GC6498@faui40p.informatik.uni-erlangen.de>
From: Brian E Carpenter <brian.e.carpenter@gmail.com>
Organization: University of Auckland
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Date: Fri, 04 Nov 2016 17:21:57 +1300
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Subject: Re: [Anima-signaling] draft-ietf-anima-grasp-08: DULL comments discovery be performed over TCP?)
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Hi Toerless,

Broadly, I think I agree with you. I'm on a few days vacation
now, so I will pick this up in detail a bit later.

Regards
   Brian

On 04/11/2016 11:10, Toerless Eckert wrote:
> Brian:
> 
> Suggestions for 3.5.2
> 
> 1. I think SONN is not necessary best described as "limited security",
>    but "constrained functionality". Therefore i would suggest
>    to use "Constrained functionality Instances" as the title.
>    imited Security such as DULL is also well in scope of 
>    "Constrained functionality".
> 
> 2. The initial text for DULL says:
> 
>    "2) During initialisation, before a node has joined the applicable trust infrastructure, [I-D.ietf-anima-bootstrapping-keyinfra], it is
>       impossible to secure messages."
>    
>    This was i think suggested by the anima-bootstrap team before it
>    decided that it wants mDNS. At that time i thought we would also
>    use one objective for both BRSKY and ACP, therefore ACP was never
>    mentioned in this text. Which now hits us.
> 
>    I would suggest changing the text so that:
> 
>    a) it will allow ACP discovery to use DULL GRASP.
>    b) it will allow any other services with similar requirements to
>       use DULLG GRAP
>    c) the text can continue stay unchanged whether or not BRSKY
>       will use DULL GRASP.
>       
> Suggested text:
> 
>   2) Services may need to perform neighbor discovery without 
>      being able to use pre-existing security associations.
>      This includes discovery of candidate ACP neighbors 
>      [I-D.ietf-anima-autonomic-control-plane], discovery of bootstrap
>      proxies [I-D.ietf-anima-bootstrapping-keyinfra] or for (example)
>      services in networks only using GRASP without being fully autonomic
>      (eg: no ACP).
> 
>      [unmodified:]
>      Such usage MUST be limited to link-local operations and MUST be
>      confined to a separate insecure instance of GRASP with its own copy
>      of all GRASP data structures.  This instance is nicknamed DULL -
>      Discovery Unsolicited Link Local.
> 
>      ...
> 
>      [modify:]
>      A responder MUST silently discard any message referring to a GRASP
>      Objective that is not directly part of the bootstrap creation
>      process.
>      [to:]
>      A responder MUST silently discard and ignore any message referring to
>      a GRASP Objective that is not directly part of the service(e) 
>      that require this insecure discovery.
> 
> Also, to optimize / minimize signaling, i'd love to see change:
>   A responder MAY send a Discovery Response message
>   A responder SHOULD NOT send a Discovery Response message
> 
> FInally: i have some decades of pain optimizing this type
> of fast & lightweight discovery - IGMP/MLD/PIM, so i have a lot
> of opinions on the details. Let me summarize them below, and
> you decide if/which of these might be useful to add (with rewording as
> you like) to the GRASP spec:
> 
>      - "Announcements" in the following means LL-multicast of 1 or more
>        packets needed to cover all the necessary insecure LL objectives
>        that need to be announced. IMHO those "Announcements" are best
>        all Flood-Synchroniation messages (Discovery messages would
>        require another round of exchanges).
> 
>      - Announcements are send periodic. Good default is 30 seconds.
> 
>        Periodic announcements really only needed when connections are
>        established that do not affect link-state on the neighbors
>        (eg: inside a LAN, between switches etc..).
> 
>      - On link-up, announcments are sent repeated N-times to allow
>        fast discovery in the presence of loss probability. N=2 is a good
>        default. The periodic timer is then reset.
> 
>      - On reception of Announcements from a previously unknown 
>        neighbor, we also send N-time repeated Announcements and reset
>        our periodic timer.
>      
>      - Announcements should allow for a "Generation-ID" feature for
>        each objective that indicates that the objective was restarted
>        without memory of prior state. This means that any followup
>        action for that objective (eg: building a connection to the
>        objetive, BRSKY, ACP,..) need to be restarted. Upon change of
>        Generation-ID, we also send N-time repeated Announcements and
>        reset periodic timer.
>      
>      - To deal with link-up-flaps and other issues, there should be an
>        exponential backup sending triggered announcements since
>        the lasst triggered announcements (1,2,3,8,16).
>      
>      - Platforms often indicate link-up before packets can actually
>        be send. Trigered announcements do need to send accordingly
>        delayed to avoid these platform issues.
> 
> 
> Cheers
>     Toerless
>