Re: [Anima] ACP -10 [was Re: I-D Action: draft-ietf-anima-autonomic-control-plane-08.txt]

Brian E Carpenter <> Thu, 21 September 2017 02:51 UTC

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To: Toerless Eckert <>
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From: Brian E Carpenter <>
Organization: University of Auckland
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Date: Thu, 21 Sep 2017 14:51:48 +1200
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Subject: Re: [Anima] ACP -10 [was Re: I-D Action: draft-ietf-anima-autonomic-control-plane-08.txt]
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On 21/09/2017 05:07, Toerless Eckert wrote:
> Thanks, Brian
> a) i will fix the ABNF with next update (for Shengs review).


> b) Given the order of likely last calls, i will suggest in the bootstrap meeting that we
>    define the AN_Registrar objective authoritatively in ACP and BRSKI adds to it the
>    "BRSKI" method. BRSKI already should have no issue having ACP as normative reference.
>    Lets see how that discussion goes.

Works for me. Just decide whether you want AN_registrar or AN_join_registrar.
> c) Given my ABNF/CDDL dyslexia, would you mind to propose a correct CDDL for the
>    objective-value structure to include the TTL and method, eg: fixup the following:
>>>   objective-value = [ sender-ttl, method-list [, future-extensions]* ]
>>>   method-list = [ method ]*1
>>>   methd = BRSKI-TLS | EST-TLS | ...
>>>   sender-ttl = NUM

I would go for this:

objective-value = [ sender-ttl, method-list, *[ future-extensions ] ]
method-list = [ +method ]
method = "BRSKI-TLS" / "EST-TLS"
sender-ttl = 0..255
future-extensions = any

The "+" prefix means 1 or more in CDDL and "*" means zero or more.
The commas in lists like [+method] are implied. (I checked
this fragment with the CDDL tool.)

I used strings for the method for simplicity; if you want to save a few
bytes you could use symbols but then they have to be assigned values like
and you end up with another IANA registry in your life.

>    If we do not get further feedback from the WG supporting my simple TTL=255 approach,
>    i would rather go with this structure approach, so that we can let the TTL disussion
>    take its natural course (figure out it should be 255 over 10 years ;-P). Primarily,
>    because i like the idea to show off a bit the flexiblity of GRASP for the objective
>    value being a structure. ANd because it would be a good reference for further objectives
>    where we want to discover/select closest instance (and we didn't include this into the
>    GRASP document proper).
> Cheers
>     Toerless
>>>   (pretty sure i didn't get the CBOR template not right, but i am sure you get the idea)
>> Not only do I get the idea, I tested it out many months ago; actually after the
>> discussions in Berlin, I think. In my Pythonic world it was very easy, but it is
>> indeed a bit more complicated than the 255-N method.
>>> That way, the recipient can compare sender-ttl with the TTL of the received objective
>>> and threeby figue out which one is closest.
>>> I fine either way. I just tried to go for the most simple, logical option.
>> Right, so the question for the WG (are you all listening?) is whether we
>> want to defend the value of the loop count in limiting propagation of multicast
>> messages. (Remember that it has another role in negotiation sessions, where
>> it really is a loop-prevention counter.)
>> I will note that in testing on looped topologies I have seen looped multicasts
>> dropped because of the session ID; theoretically that is sufficient, and the
>> loop count is logically redundant.
>> Otherwise, me happy.
>> Thanks again for all the work,
>>     Brian