Re: [Pce] Implementation option of draft-ietf-pce-stateful-interdomain-01.txt

"Stone, Andrew (Nokia - CA/Ottawa)" <andrew.stone@nokia.com> Thu, 11 March 2021 16:11 UTC

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From: "Stone, Andrew (Nokia - CA/Ottawa)" <andrew.stone@nokia.com>
To: "olivier.dugeon@orange.com" <olivier.dugeon@orange.com>, Dhruv Dhody <dhruv.ietf@gmail.com>
CC: "pce@ietf.org" <pce@ietf.org>
Thread-Topic: [Pce] Implementation option of draft-ietf-pce-stateful-interdomain-01.txt
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Archived-At: <https://mailarchive.ietf.org/arch/msg/pce/FmTTCPCX_f743X3g-r1yK04XUyY>
Subject: Re: [Pce] Implementation option of draft-ietf-pce-stateful-interdomain-01.txt
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Hi Olivier,

Thanks for pointing this out. I think the presentation slide wording might have been a bit stronger than what is currently written in the posted draft, as the text does not prohibit the use of RRO but rather acknowledge and document that there are implementations which skip inclusion of SR-RRO (Nokia implementation does send SR-RRO), so it documents how to handle this scenario on the PCE. The text indicates that SR-RRO may or may not be included, and if omitted the PCE is to fallback to treating the ERO “like” it was an RRO.

https://datatracker.ietf.org/doc/html/draft-koldychev-pce-operational-03#section-6

   A PCC MUST send an (possibly empty) ERO/SR-ERO/SRv6-ERO in the PCRpt
   message for every LSP.  A PCC MAY send an SR-RRO/SRv6-RRO for an SR-
   TE/SRv6-TE LSP (respectively).  A PCE SHOULD interpret the RRO/SR-
   RRO/SRv6-RRO as the actual path the LSP is taking but MAY interpret
   only the ERO/SR-ERO/SRv6-ERO as the actual path.  In the absence of
   an RRO/SR-RRO/SRv6-RRO a PCE SHOULD interpret the ERO/SR-ERO/SRv6-ERO
   (respectively) as the actual path for the LSP.


I think the potential interdomain stitching label case you point out and the S-Flag defined in RFC8664 mentioned by Dhruv during the meeting seem to be valid use cases where an SR-RRO would need to be included.

Thanks!
Andrew

From: Pce <pce-bounces@ietf.org> on behalf of "olivier.dugeon@orange.com" <olivier.dugeon@orange.com>
Organization: Orange Labs
Date: Thursday, March 11, 2021 at 5:17 AM
To: Dhruv Dhody <dhruv.ietf@gmail.com>
Cc: "pce@ietf.org" <pce@ietf.org>
Subject: Re: [Pce] Implementation option of draft-ietf-pce-stateful-interdomain-01.txt


Hello Dhruv, all,

Following the presentation done during the IETF meeting, please find the link to the presentation: https://datatracker.ietf.org/meeting/110/materials/slides-110-pce-32-inter-domain-00

I also not a major point to take into account following the presentation of draft PCEP Operational Clarification (draft-koldychev-pce-operational) see https://datatracker.ietf.org/doc/draft-koldychev-pce-operational/ and https://datatracker.ietf.org/meeting/110/materials/slides-110-pce-34-operational-clarification-00:

 => In this draft, authors propose to use SR-ERO/SRv6-ERO and to NOT use SR-RRO/SR-v6-RRO for Segment Routing.

As a consequence for the stateful inter-domain draft, proposed option d1, d2 and d3 become invalid as it uses the RRO to convey the Stiching Label. Thus, only option d4 with a specific new sub-Object to convey the Stitching Label remains valid.

As usual, comments are welcome.

Regards

Olivier
Le 26/02/2021 à 05:35, Dhruv Dhody a écrit :
Hi Olivier,

Thanks for starting this thread.

As a WG participant...

On Tue, Feb 23, 2021 at 12:05 AM <olivier.dugeon@orange.com<mailto:olivier.dugeon@orange.com>> wrote:
Dear all,

According to the remark about implementation we got during the WG call
for adoption, we would start a new thread to discuss this point.
The goal isto prepare the discussion for next IETF meeting and reach a
consensusin order to edit revision 2 of the draft.

The stitching label principle requires at least a certain number of
modifications in the current PCEP version:

 a) A new PCE Capability to announce the inter-domain behaviour
 b) A new PCE Association Group to associate the local paths identifier
    to the inter-domain identifier
 c) new PCEP Errors to manage the Stitching Label exchange
 d) A mechanism to convey the Stitching Label

If there is no other choice than to reuse existing PCEP Objects by
allocating new code points for modifications a-c,there is several
options for point d, which we have tried to list below:

 d1) Use ERO and RRO in conjunction to new Path Setup code points as
     described in version 01 of the draft. It is the simplest
     implementation but as mention by Dhruv, each time a new path
     enforcement appear, a new PST code point must be allocated.
     For example, when Segment Routing v6 will be standardized, we must
     allocate a new Stitching label PST code point for SRv6.
 d2) Use ERO and ERO in conjunction to a new flag in LSP. Simple as for d1,
     but need to use the LSP Extended Flag draft as all LSP flags have been
     already allocated.
 d3) Same as d2 but find another place for the flag e.g. SRP or LSPA Object.
 d4) Define a new PCEP sub-Objet TLV within the LSP Object to convey the
     stitching label. This is more independent but need extra parsing from
     an implementation point of view.

My preference would for d2 or d3 (in that order).
LSP Extended Flag is adopted by the WG and is ready for prime-time use -- let's use it :)
Authors of LSP Extended Flag are waiting for the draft blockade to be lifted to post the -00 WG I-D.

Thanks!
Dhruv

Please, give us your opinion about these different options and don't hesitate
to propose others.

Regards

Olivier on be-half of co-author's




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