Re: [Pce] draft-hsd-pce-sr-p2mp-policy wiki comments and action.

Aijun Wang <wangaijun@tsinghua.org.cn> Tue, 23 March 2021 07:00 UTC

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From: "Aijun Wang" <wangaijun@tsinghua.org.cn>
To: "'Dhruv Dhody'" <dd@dhruvdhody.com>, "'Bidgoli, Hooman \(Nokia - CA/Ottawa\)'" <hooman.bidgoli@nokia.com>
Cc: <pce@ietf.org>
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Subject: Re: [Pce] draft-hsd-pce-sr-p2mp-policy wiki comments and action.
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Hi, 

 

My consideration is that if the solution depends on the distribution protocol among the underlay nodes to accomplish the task, then PCE should follow the procedures described in RFC8231, RFC8281 etc. That is to say, in such situation, the instruction from the PCE needs only to be sent to the headend of the path.

 

And, if the solution depends solely on the computation of the PCE, and PCE should interact not only the headend node, but also the transit node, tail-end node, follow the PCECC approach is more clear.

Mixed of these two solutions should be avoided.

 

 

Best Regards

 

Aijun Wang

China Telecom

 

From: pce-bounces@ietf.org <pce-bounces@ietf.org> On Behalf Of Dhruv Dhody
Sent: Monday, March 22, 2021 12:48 PM
To: Bidgoli, Hooman (Nokia - CA/Ottawa) <hooman.bidgoli@nokia.com>
Cc: pce@ietf.org
Subject: Re: [Pce] draft-hsd-pce-sr-p2mp-policy wiki comments and action.

 

Hi Hooman,

 

On Thu, Mar 18, 2021 at 10:06 PM Bidgoli, Hooman (Nokia - CA/Ottawa) <hooman.bidgoli@nokia.com <mailto:hooman.bidgoli@nokia.com> > wrote:

Hi Dhruv

I am very confused by your messaging. 

Originally it was pointed out that the draft should follow PCECC/CCI.
The authors explained why they feel that is not a good fit.

Now you are mentioning get in part with RFC 8231, 8281 etc... which is a new input. Thank you.

 

I apologize if I was not clear. As I said in the mail, I still feel PCECC is the way to go. What I want to highlight is that if you consider it as an LSP operation instead, then it should be built on RFC 8623 (P2MP) instead. 

 

The 'recap' was to show how the extensions in PCEP have been done for SR and P2MP in the past in a consistent way. 

 

 

The authors/co-authors have  tried to keep the draft in par with all the RFCs that you mentioned as much as possible. As it is mentioned in the draft clearly. That said this is new concept and there is a need for a new PCE concept and deviation, hence the draft ūüėä and the purpose of IETF.

RSVP-TE P2MP is built via S2Ls.
Replication segment is nothing like S2L, replication segment can be connected via unicast SR.

 

If you claim that the replication segment can not use RFC 8623, that gives it more of a reason to not consider it as an LSP operation in the first place.  

 

Again we are open for any constructive feedback on how this draft can be improved, in the boundary of 
https://datatracker.ietf.org/doc/draft-ietf-spring-sr-replication-segment/
https://datatracker.ietf.org/doc/draft-ietf-pim-sr-p2mp-policy/

 

Just to clarify, my feedback is on your choice of PCEP procedure and encoding for the replication segment taking existing PCEP extensions/procedures in mind.  Hope the discussion was useful, it was for me...

 

Thanks! 

Dhruv (as a WG member)

 

Regards
Hooman


-----Original Message-----
From: Pce <pce-bounces@ietf.org <mailto:pce-bounces@ietf.org> > On Behalf Of Dhruv Dhody
Sent: Thursday, March 18, 2021 8:01 AM
To: pce@ietf.org <mailto:pce@ietf.org> 
Subject: Re: [Pce] draft-hsd-pce-sr-p2mp-policy wiki comments and action.

Hi,

Speaking as a WG member...

Let's continue the discussion on considering the replication segment as an LSP v/s PCECC operation.

I just wanted to quickly recap -

- We have stateful operations for RSVP-TE: RFC 8231, RFC 8281
- We then introduced SR with a minimal extension of new PST and a new SR-ERO subobject: RFC 8664
- We supported P2MP stateful operations for RSVP-TE with RBNF change in PCEP messages: RFC 8623

We have always tried our best to maintain consistency between RSVP-TE and SR in PCEP.

Now, if one considers the Replication segment as an LSP operation, IMHO it needs to be built on RFC 8623 P2MP LSP operations. The current approach does not build on RFC 8623 instead uses the multi-path technique (related to ECMP in P2P [1]). This would deviate from RFC
8623 significantly.

On the other hand, considering the replication segment as a PCECC/CCI operation gives you more leeway to choose an encoding with a new CCI Object type for the replication segment and it could be independent of RFC 8623.

I *still* feel PCECC makes more sense at the higher level too (because of the additional instruction to the leaves and coordination required). Even if one disagrees with that and considers it an LSP operation, it then needs to build on RFC 8623. The current "mashup"
approach (i.e. it is an LSP operation but does not follow P2MP LSP
encoding) does not work well in maintaining consistency within our extensions.

Thanks!
Dhruv (as a WG member)
[1] https://datatracker.ietf.org/doc/draft-koldychev-pce-multipath/

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