(Hard to follow Acee’s post – especially for entertainment value)
Bruno –
I think that we do want some less awkward text. So I am proposing to add the
following into the Introduction:
“Label Imposition is the act of modifying and/or adding labels to the outgoing
label stack associated with a packet.
This includes:
o replacing the label at the top of the label stack with a new label
o pushing one or more new labels onto the label stack.
The number of labels imposed is then the sum of the labels which are replaced
and the labels which are pushed.
See [RFC3031] for further details.”
The BMI definition then becomes:
“Base MPLS Imposition MSD (BMI-MSD) signals the total number of MPLS
labels which can be imposed, including all service/transport/special
labels.”
Does this work??
Les
From: Acee Lindem (acee)
Sent: Wednesday, October 03, 2018 2:05 PM
To: Bruno Decraene <[email protected]>
Cc: Routing Directorate <[email protected]>;
[email protected]; [email protected]; Alvaro Retana
<[email protected]>; [email protected]; Jeff Tantsura
<[email protected]>; Les Ginsberg (ginsberg) <[email protected]>; MEURIC
Julien IMT/OLN <[email protected]>
Subject: Re: [Lsr] [RTG-DIR] RtgDir Review:
draft-ietf-isis-segment-routing-msd-15
Hi Bruno,
On Oct 3, 2018, at 10:07 AM,
[email protected]<mailto:[email protected]> wrote:
Hi Acee,
From: Acee Lindem (acee) [mailto:[email protected]]
Hey Bruno, Jeff, Les,
Have we agreed on the precise definition of “label imposition”?
Thanks for asking.
Not so far.
We don’t necessarily need to agree on a precision definition of “label
imposition”. In my latest email (a few hours ago), I proposed to reuse the
phrasing from RFC 3031, which does not use that term. If we are fine with using
RFC 3031 terms, that would be fine for me.
Since the MSD type has always been defined in terms of “Imposition” in both the
OSPF and IS-IS MSD drafts, I think it would be better to clarify any
ambiguities the text Les quotes below.
Of course, we don’t want to get too bogged down in semantics as has happened in
the past: https://www.youtube.com/watch?v=-P8IYKxpqG0
Thanks,
Acee
Thanks,
--Bruno
Thanks,
Acee
From: Lsr <[email protected]<mailto:[email protected]>> on behalf of
Bruno Decraene <[email protected]<mailto:[email protected]>>
Date: Wednesday, October 3, 2018 at 4:37 AM
To: Jeff Tantsura <[email protected]<mailto:[email protected]>>
Cc: Routing Directorate <[email protected]<mailto:[email protected]>>,
"[email protected]<mailto:[email protected]>"
<[email protected]<mailto:[email protected]>>,
"[email protected]<mailto:[email protected]>"
<[email protected]<mailto:[email protected]>>, Alvaro Retana
<[email protected]<mailto:[email protected]>>,
"[email protected]<mailto:[email protected]>" <[email protected]<mailto:[email protected]>>, "Les
Ginsberg (ginsberg)" <[email protected]<mailto:[email protected]>>, MEURIC
Julien IMT/OLN <[email protected]<mailto:[email protected]>>
Subject: Re: [Lsr] [RTG-DIR] RtgDir Review:
draft-ietf-isis-segment-routing-msd-15
Jeff,
From: Jeff Tantsura [mailto:[email protected]]
Sent: Tuesday, October 02, 2018 8:28 PM
To: DECRAENE Bruno IMT/OLN; Alvaro Retana; MEURIC Julien IMT/OLN; Les Ginsberg
(ginsberg)
Cc: [email protected]<mailto:[email protected]>;
[email protected]<mailto:[email protected]>; [email protected]<mailto:[email protected]>;
[email protected]<mailto:[email protected]>
Subject: RE: [RTG-DIR] RtgDir Review: draft-ietf-isis-segment-routing-msd-15
Gents,
I’m 100% with Les here, going into platform/asic specifics within this document
would inevitably create ambiguity.
Absolutely.
And nobody is asking for this.
Cheers
--Bruno
Cheers,
Jeff
On Oct 2, 2018, 11:20 AM -0700, Les Ginsberg (ginsberg)
<[email protected]<mailto:[email protected]>>, wrote:
Bruno –
Trimming the thread…
[Les2:] Label imposition is meant to cover both the SWAP operation and the PUSH
operation. In the example you provided above where a label stack of “12” is
replaced by a label stack of “14,15” the number of labels “imposed” is 2.
[Bruno2] In that case, I definitely think that the discussion was useful and
that this point needs to be clarified in the document.
Whether you choose to call that (1 POP, 2 PUSH) or (1 SWAP, 1 PUSH) or simply
a SWAP isn’t relevant here (though it might matter to folks like the RFC 3031
authors).
With that ibn mind, here is proposed text:
“Base MPLS Imposition MSD (BMI-MSD) signals the total number of MPLS
labels which can be imposed, including all service/transport/special
labels. Imposition includes swap and/or push operations.
If the advertising router performs label imposition in the context of
the ingress interface, it is not possible to meaningfully advertise
per link values. In such a case only the Node MSD SHOULD be
advertised.”
[Bruno2] Given that the term “imposition” does not seem to be defined within
the IETF, I would still favor a formal definition not using it. e.g. “BMI-MSD
advertises the ability to increase the depth of the label stack by BMI-MSD
labels”.
Alternatively, I’d propose the following rewording which seems clearer to me:
OLD: Imposition includes swap and/or push operations.
NEW: A swap operation counts as an imposition of one label; just like one push
operation.
[Les3:] This gets into implementation specific issues that I would really like
to avoid.
For example, some implementations perform one and only one “operation”.
Conceptually that may involve a swap and a push – but from the internal
implementation POV it is simply one operation. And this may be true regardless
of how many labels are involved. Other implementations might perform this in
several discrete steps. The language we use here should not imply anything
about how many labels are associated with a specific operation.
The term “increase” isn’t accurate because in the case of a swap there is no
increase, yet the label which is replaced is counted.
https://tools.ietf.org/html/rfc3031#section-3.10 is relevant here.
The term “imposition” is generic – and as Alvaro has pointed out is used in RFC
4221. And the language proposed above does define the relationship between
“swap and push” and “imposition”.
I appreciate your desire for clarity – and I am still open to new language –
but at this point I still think what I proposed is the most accurate.
Les
Thanks,
--Bruno
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