Re: [Anima-bootstrap] Brian: GRASP parameter for registrar discovery by proxy

Brian E Carpenter <brian.e.carpenter@gmail.com> Tue, 21 February 2017 19:45 UTC

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To: Toerless Eckert <tte@cs.fau.de>
References: <20170221155002.GA8168@faui40p.informatik.uni-erlangen.de>
From: Brian E Carpenter <brian.e.carpenter@gmail.com>
Organization: University of Auckland
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Date: Wed, 22 Feb 2017 08:44:49 +1300
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Subject: Re: [Anima-bootstrap] Brian: GRASP parameter for registrar discovery by proxy
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Hi Toerless,

First of all, did you look at draft-carpenter-anima-ani-objectives-01
and https://www.cs.auckland.ac.nz/~brian/graspy/brski/ ?

I am not defending the details in those but they do indicate what's
possible with GRASP, and how I think this could be solved.

More below:

On 22/02/2017 04:50, Toerless Eckert wrote:
> Hi Brian
> 
> In the anima bootstrap meeting we tried to figure out the necessary
> GRASP message elements for discovery of registrars by proxies. And make
> it extensible.
> 
> If you check:
> 
> http://etherpad.tools.ietf.org:9000/p/anima-boostrapping?useMonospaceFont=true
> 578 - 608

That seems to go back to using discover/response. Wrong answer, IMHO; flooding
is simpler: fewer messages and richer semantics. I'm going to assume that below. 

> We may have a bunch of different possible proxy behaviors:
> 
>   - TCP circuit proxy in conjunction with HTTPs
>   - UDP proxy in conjunction with CoAP
>   - IPinIP proxy in conjunction with either HTTPs or CoAP

Sure. In the above, these are what I call the "method" amd they would be
defined by a text string name, which makes it easy to add new ones.
They could be anything; in my examples I used "BRSKI-TLS" and "BRSKI-COAP"
but "tcp-circuit" etc would work fine too. Whatever you want.
 
> MichaelR's text was currently suggesting to indicate in the GRASP message
> what the registrar supports via the locators:
> 
>     locator1  = [O_IPv6_LOCATOR, fe80::1234, 6,  <any,eg:443>]
>     locator2  = [O_IPv6_LOCATOR, fe80::1234, 17, <any,eg:5683>]
>     locator3  = [O_IPv6_LOCATOR, fe80::1234, 41, nil]
> 
> The first line would indicate TCP circuit proxy, the second UDP proxy,
> the third one IPinIP proxy.
> 
> I am quite uncomfortable to indicate the desired proxy behavior
> purely via the IP protocol field in a locator (6, 17, 41). It already
> is IMHO underspecified,  eg: unclear why the UDP proxy would (only) support
> CoAP, and what actually the IPinIP stack supports (CoAP, HTTPs, ...).

Correct. It's insufficient because it cannot separate the upper layer cases.

(Also, using link-local examples is an oversight, surely: this should
be an ACP address, e.g. fdab:dead:beef::1234, I think.)

> So, how/where would we most easily indicate the stack in the GRASP
> response ? For example:
> 
>     locator1  = [O_IPv6_LOCATOR, fe80::1234, 6,  <any,eg:443>, tcp-circuit]
>     locator2  = [O_IPv6_LOCATOR, fe80::1234, 17, <any,eg:5683>, coap-udp]
>     locator3  = [O_IPv6_LOCATOR, fe80::1234, 41, nil, tcp-ip-in-ip]
>     locator3  = [O_IPv6_LOCATOR, fe80::1234, 41, nil, coap-ip-in-ip]

No, that would be a protocol change by adding an extra field to the locator
syntax. However, this is already covered by a feature of the Flood message
which we added a while back. Each item in a flood message is optionally associated
with its own locator:

flood-message = [M_FLOOD, session-id, initiator, ttl, 
                 +[objective, (locator-option / [])]]

so we'd send several copies of the objective, each with its own "method"
and locator.

So for example we'd flood 
the objective ["AN_join_registrar", F_NEG, 6, ["tcp-circuit"]]
with locator  [O_IPv6_LOCATOR, fdab:dead:beef::1234, 6, 443]
and an objective ["AN_join_registrar", F_NEG, 6, ["coap-udp"]]
with the locator [O_IPv6_LOCATOR, fdab:dead:beef::1234, 17, 5683]

The could be sent all in one Flood message, or in separate ones,
possible from different sources if there were actually two registrars,

Truly, if you read the draft and eyeball the Python, you can see how it
works.

If you really don't want to use flooding, it gets more tricky. Discovery
alone won't do the trick in a simple way. I know how to do it but it will
involve more messages.

Regards
   Brian

> 
> Thanks!
>     Toerless
>