Re: [Taps] call for agenda items at TAPS IETF-104

[tom petch <[e-mail]>]

----- Original Message -----
From: "Michael Welzl" <[e-mail]>
Sent: Thursday, March 07, 2019 8:32 AM
>
> Very sorry for the silence. I can only speak for myself, but here's an
example of why this one person was silent:
> - When you created your issue on multicast in github, I thought of
answering (positively), but then thought that the repo is about to move,
and it would probably be better to delay things until the move is
finished.
> - Then, the issue was overruled by your email. I read it and found it
interesting, but hoped for someone else to answer because, frankly, I
was afraid to make a fool of myself ... because I know almost nothing
about YANG.
>
> But now I'll be brave  :)   I'll go ahead and ask: how exactly is this
YANG proposal more than just a syntax change?  What would it give us?
> (I understand that YANG can be automatically parsed / checked by some
tools, but... what does THAT give us?)

Yes, indeed.  YANG is a DDL created to provide definitions of data
structures that need to be read and/or written when managing networks or
similar systems, so it matches well with BGP or LISP, NAT or QOS.  It is
verbose (a reaction IMHO to ASN.1).  It lacks, for me, rigour, formal
underpinnings, which shows up in quirks, corner cases and in the lengthy
ABNF definition of it.  It has got constraints - 'must' 'when' range of
values or length - so you can specify that the MTU must be present and
be in a different range depending on which interface type is referenced.

It is closely tied to XML and Netconf (as a most fleeting glance at
RFC7950 shows); repeated talk of decoupling it have yet to lead to
action.  The syntax was chosen to be C-like (but not C).

It has no sense of document order.  The permitted range of values can be
tied to what you might see in an IETF protocol (although a string can be
18446744073709551615).  Enumerations can specify a value (along with a
string) but the value is documentation only - it does not appear on the
wire.  There is no sense of precedence between, say, Prefer and Require.
Capital letters are not prohibited, rather discouraged so few people use
them.

What does it offer TAPS?  Mmm I thought TLS foolish when it defined its
own DDL but over time, have come to appreciate that choice.

Tom Petch

> Also, I actually see 3 separable things being proposed here:
>
> 1) the YANG model
>
> 2) multicast support  (I find your conclusion that not much needs to
change interesting!  Though the example you're giving (joining an SSM
channel) is only a part of what we'd need, as you also say...)
>
> 3) applying preferences to addresses and port numbers  (which you seem
to take for granted in your draft, but which I don't think is supported
by our current document).
> Side note: unless I'm mistaken, this wouldn't fit our structure well:
e.g. a port number would then be a Transport Property that has a certain
value, but also has a preference, but currently we say that a Transport
Property has "one of a set of data types", one of which is a Preference.
Isn't that structure too limiting? Or am I missing something?
>
> I guess that 2) needs 3), but perhaps it's useful to see 2) and 3) as
separate... maybe there are other use cases for 3) alone ?
> IMO, all of these things are interesting, and would be good to discuss
on site. However, I doubt that we can deal with them all in only 15
minutes  :-)
>
> Cheers,
> Michael
>
> PS: Travis is down, or something. At least the "Editor's Copy" links
don't currently work.
>

> > On 7 Mar 2019, at 04:55, Holland, Jake <[e-mail]> wrote:
> >
> > Hi taps,
> >
> > (Trying again, but simpler.)
> >
> > I'm looking for a consensus yes or no answer:
> >
> > Is a normative config input format an interesting and useful
> > direction?
> >
> >
> > The idea is to add functionality like this, in taps-interface:
> >
> >  newPre = PreConnection.NewFromJson('''{
> >    "remote-endpoint":{
> >      "hosts":[
> >        { "host":"example.com" }
> >      ]
> >    }
> >  }''')
> >
> > With a fully specified json input format that can provide all the
> > configurable values.
> >
> >
> > If no, I'll move on and assume I just don't understand taps goals.
> >
> > If yes, I'd like 15 minutes to discuss in Prague, and keep reading:
> >
> > I think a full definition of an input json format can be exactly
> > specified by a YANG model. (With xml for free, if you want it.)
> >
> > I tried to sketch a start at what a YANG model for this might look
like:
> >
https://tools.ietf.org/html/draft-jholland-taps-api-yang-00#section-3
> >
> > I'm not a YANG expert yet, and it's not much of a model.  And it's
very
> > far from complete.  But it compiles, and all the examples in the
draft
> > validate against that model with libyang.  If it's worthwhile, I
think
> > something like this can be good (and extensible!), if done right.
> >
> > I believe something along these lines would sharpen up
taps-interface
> > a lot. (After filling in all the taps-interface properties.)
> >
> >
> > The reason I'm asking is because right now, taps-interface to me
> > seems _almost_ really good, except too confusing and vague to
actually
> > build an API that can replace BSD sockets.  I think with a solid
config
> > format with normative and testable examples, that could be fixed.
> >
> > If consensus says "interesting", I'll want 15 minutes to discuss it,
and
> > to start digging into how to make it good.  (And also to add
multicast
> > support to the model and at least one implementation.)
> >
> > Thanks for your consideration.
> >
> >
> > Cheers,
> > Jake
> >
> >
> >
> > On 2019-03-04, 17:19, "Holland, Jake" <[e-mail]> wrote:
> >
> >    Hi taps folks,
> >
> >    TL;DR: I think the spec should have a YANG model and I want to
use it
> >    to get multicast support in an implementation.
> >
> >
> >    I recently started digging into the taps API with the intent of
adding
> >    multicast support, but it looks like it's basically already
there, as
> >    far as it goes[*].
> >
> >    But I ended up with a higher-level comment, so I thought I'd
raise it
> >    to the wg and ask what you all think.
> >
> >    I found the whole "abstract interface" approach a little too
> >    loosey-goosey, so I thought I'd try to suggest a way to tighten
it up.
> >
> >    My goal with this is to make it much more clear (to the point of
being
> >    mechanically checkable) precisely what a compliant API provides.
> >
> >    I'm not attached to the structure I'm proposing or to any of the
> >    particulars in the straw-man I've posted, but if it's not
tightened up
> >    with something at a similar level of concreteness, I'm concerned
that
> >    different implementations will be not only incompatible in random
> >    underspecified corner cases (like BSD sockets today when you try
to make
> >    cross-platform C code), but also are likely to end up with very
many
> >    important differences that would make the whole taps effort more
or less
> >    moot.
> >
> >    In a world where we end up with a doc at the level of abstraction
I'm
> >    currently seeing in draft-taps-interface, it seems to me that if
2
> >    different API implementations were written in the same language,
it'll
> >    be prohibitively difficult for an app to migrate from using one
to using
> >    the other, just because so many aspects of it are left open to
the
> >    implementors.
> >
> >    In that context, I thought a YANG model would be useful here to
> >    provide a cross-platform way to specify what exact properties and
> >    objects exist, an exact format in which the values can be
specified, and
> >    what exact semantics they have, while still allowing for a sane
> >    extension path and language-specific implementation details.
> >
> >    I'm thinking some language a bit like the first bullet in Section
4.2 of
> >    taps-interface:
> >
> >      A compliant implementation SHOULD provide a
language-appropriate way to
> >      configure a PreConnection using YANG instance data for this
model, and
> >      SHOULD provide an API that outputs the YANG instance data for
an
> >      established Connection.
> >
> >      An implementation MAY also provide appropriate APIs for
directly editing
> >      the objects without using YANG.  It's RECOMMENDED where
possible to use
> >      names that mechanically translate to the names in the YANG data
model,
> >      using capitalization and punctuation conventions as expected
for the
> >      language of the implementation.
> >
> >    And then of course a YANG model:
> >    https://datatracker.ietf.org/doc/draft-jholland-taps-api-yang/
> >    (draft-jholland-taps-api-yang)
> >
> >    If this seems useful, it will need lots of refining.  I'll be
surprised
> >    if any part of it survives exactly as written.  It's a quick and
> >    dirty attempt to concretize a few of the things I saw listed in
> >    draft-ietf-taps-interface, as a starting point to fill out if it
seems
> >    useful.
> >
> >    But the model parses, and the example data instances in the draft
> >    parse against the model (all with libyang).
> >
> >    One of the main reasons I'm doing this is because it seems to me
what's
> >    specified in taps-interface-02 today is missing some key
features, like
> >    an enumeration of the properties in the Local/RemoteEndpoint
examples in
> >    section 5.1.  And I don't see that listed as an open issue in
github,
> >    which surprised me a bit.
> >
> >    I think oversights like this will become immediately and
painfully
> >    obvious when there's a reference implementation that includes a
YANG
> >    parser and an explicit data model, as opposed to the combing of
the
> >    document and a sort of eyeballed comparison to NEAT that I tried
> >    this week to reach that conclusion (which I found challenging
even
> >    though I thought both the document and the library were mostly
pretty
> >    well written).
> >
> >    The whole thing at this point just smells to me much more
abstract than
> >    it really has to be or than it's really useful to be, which
bothers me
> >    because the idea of replacing BSD sockets with something usable
seems
> >    like such a great idea.  I'd like this to be something I can
actually
> >    use in a way that makes my life easier someday soon.
> >
> >    But I think I'm at the point where I need a sanity check to see
if I'm
> >    just missing something, or if this seems like a useful direction.
> >
> >    Thoughts?  Suggestions?   Worth discussing in Prague?  (If so,
can I
> >    get a slot?)
> >
> >    Cheers,
> >    Jake
> >
> >    *:
> >    I concluded that there's no reason multicast couldn't be
supported
> >    today, if there were an implementation that could reasonably
claim to be
> >    compliant, by just adapting some of the examples in
> >    draft-ietf-taps-interface-02 and understanding the semantic
meaning of
> >    multicast address spaces inside the API.
> >
> >    For example, I couldn't find any reason this can't be expected to
set
> >    up an SSM channel subscription without any further ado, given a
sane
> >    implementation that supports it:
> >
> >      RemoteSpecifier := NewRemoteEndpoint()
> >      RemoteSpecifier.WithIPv4Address(192.0.2.21)
> >
> >      LocalSpecifier := NewLocalEndpoint()
> >      LocalSpecifier.WithPort(30000)
> >      LocalSpecifier.WithIPv4Address(232.252.0.2)
> >
> >      NewPreconnection(RemoteSpecifier, LocalSpecifier).Listen(...)
> >
> >    Maybe there's some value in specifying a "JoinSSM()" to override
defaults
> >    in the PreConnection, just to make sure you're specifically
asking for
> >    multicast.  I think that would be fine for native multicast, but
like I
> >    said, a much smaller point than the looseness of the API.
> >
> >    Where it gets a bit more complicated is trying to handle multiple
options
> >    for discovering a usable unicast tunnel for multicast traffic, as
> >    described in Section 2.4.1 of
draft-ietf-mboned-driad-amt-discovery-01.
> >
> >    I'd like to have a decent place to tack on an extension to this
API that
> >    can transparently, within the connection API, discover the best
available
> >    AMT relay and start using it when native joining is unavailable
(and also
> >    to provide normative controls for configuring it when there's
> >    administrative configuration to be added).
> >
> >    But that's a 2nd order question for me at this point, because in
the
> >    current TAPS API I don't see any obviously good spot to put
selection
> >    controls for that kind of tunnel discovery selection, or really a
good
> >    way to explain what it's supposed to do, if I tried to add
controls to
> >    something that's there.
> >
> >    Solving that is my main motivation for being here.  (Well, and
that
> >    the BSD socket API for multicast is kind of a disaster today.)
> >
> >    Anyway, if taps finds the whole YANG suggestion useful, I'll
probably
> >    suggest some new extensions about this, and maybe a few other
points,
> >    especially maybe around trying to put in a structure that can
support
> >    some kind of sane explicit layering.
> >
> >    But I'm not sure I can articulate those suggestions in a way I'm
sure is
> >    meaningful without first getting a more clear specification
nailed down
> >    about what's actually in the taps spec. Because right now I'm
mostly
> >    just confused about what an API implementation would really look
like,
> >    and how you could tell whether it matches the taps-interface
spec.
> >
> >
> >
> >    From: Aaron Falk <[e-mail]>
> >    Date: 2019-03-04 at 10:53
> >    To: taps WG <[e-mail]>
> >    Cc: Zaheduzzaman Sarker <[e-mail]>
> >    Subject: [Taps] call for agenda items at TAPS IETF-104
> >
> >    Hi All-
> >    What should we use our time to discuss? Let’s focus on things
that would benefit from f2f discussion, consensus building, or just
argument. :)
> >    • TAPS docs: are there open topics that need group attention?
Seems like we settled most of the remainder at the interim.
> >    • TAPS security: this seems nearly done. Anything to discuss?
> >    • Implementations: a good topic for information sharing but less
important than anything needing agreement
> >    • Mobility:
https://urldefense.proofpoint.com/v2/url?u=https-3A__tools.ietf.org_html
_draft-2Dietf-2Ddmm-2Dondemand-2Dmobility-2D17&d=DwMFaQ&c=96ZbZZcaMF4w0F
4jpN6LZg&r=bqnFROivDo_4iF8Z3R4DyNWKbbMeXr0LOgLnElT1Ook&m=pLW5gSyetfVe_ix
G4_u7qKX_VcjIqzN7Ju2BgM2rpQo&s=HUsBVBF_GhNiOk3gqY_m5qZMD-sPmBJ93GE5wd3D5
_s&e= and
https://urldefense.proofpoint.com/v2/url?u=https-3A__datatracker.ietf.or
g_doc_review-2Dietf-2Ddmm-2Dondemand-2Dmobility-2D15-2Dtsvart-2Dlc-2Dwes
terlund-2D2019-2D01-2D08_&d=DwMFaQ&c=96ZbZZcaMF4w0F4jpN6LZg&r=bqnFROivDo
_4iF8Z3R4DyNWKbbMeXr0LOgLnElT1Ook&m=pLW5gSyetfVe_ixG4_u7qKX_VcjIqzN7Ju2B
gM2rpQo&s=0YmC_XCAu4_GVYdFi0HxiKaKBpan2COYqBL1mB6bXrY&e=
> >    --aaron
> >
> >
> >
> > _______________________________________________
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