[Pce] Association Source in draft-ietf-pce-segment-routing-policy-cp-01

[Dhruv Dhody <[e-mail]>]

Hi Authors,

In
https://tools.ietf.org/html/draft-ietf-pce-segment-routing-policy-cp-01#section-4.2
,  you state -

   The Association Source MUST be set to the PCC's address.  This
>    applies for both PCC-initiated and PCE-initiated candidate paths.
>    The reasoning for this is that if different PCEs could set their own
>    Association Source, then the candidate paths instantiated by
>    different PCEs would by definition be in different PCEP Associations,
>    which contradicts our requirement that the SR Policy is represented
>    by an Association.



>
>    The Association ID MUST be chosen by the PCC when the SR policy is
>    allocated.  In PCRpt messages from the PCC, the Association ID MUST
>    be set to the unique value that was allocated by the PCC at the time
>    of policy creation.  In PCInit messages from the PCE, the Association
>    ID MUST be set to the reserved value 0, which indicates that the PCE
>    is asking the PCC to choose an ID value.  The PCE MUST NOT send the
>    Extended Association ID TLV in the PCInit messages.


But the base RFC 8697
https://www.rfc-editor.org/rfc/rfc8697.html#section-6.1.3 gave quite a bit
of leeway while setting the association source.

Consider 2 PCEs - PCE1 & PCE2, I am assuming if candidate paths are created
via two different PCEs both will be aware of SR Policy identifiers (color,
end-point, etc). When PCE1 initiates CP1, it could use the association
source as Virtual-IP or NMS (instead of PCE1). The PCE2 will learn about
the association and the corresponding SR policy parameters via the PCRpt
message which is sent to both PCEs. So when the PCE2 initiates CP2, it
could use the same association!

This was the very reason to include the flexibility in setting the
association source in RFC 8697.

Julien and I discussed this and we feel you are trying to solve the issue
of sharing an association ID between several PCEs by using a new mean than
the one in RFC 8697. If you have other reasons then please state them,
otherwise, RFC 8697 should take precedence.

Thanks!
Dhruv & Julien

PS. I quickly drew a figure if that helps (see attached)!

On Tue, Oct 27, 2020 at 8:42 PM <[e-mail]> wrote:

>
> A New Internet-Draft is available from the on-line Internet-Drafts
> directories.
> This draft is a work item of the Path Computation Element WG of the IETF.
>
>         Title           : PCEP extension to support Segment Routing Policy
> Candidate Paths
>         Authors         : Mike Koldychev
>                           Siva Sivabalan
>                           Colby Barth
>                           Shuping Peng
>                           Hooman Bidgoli
>         Filename        : draft-ietf-pce-segment-routing-policy-cp-01.txt
>         Pages           : 20
>         Date            : 2020-10-27
>
> Abstract:
>    This document introduces a mechanism to specify a Segment Routing
>    (SR) policy, as a collection of SR candidate paths.  An SR policy is
>    identified by <headend, color, end-point> tuple.  An SR policy can
>    contain one or more candidate paths where each candidate path is
>    identified in PCEP via an PLSP-ID.  This document proposes extension
>    to PCEP to support association among candidate paths of a given SR
>    policy.  The mechanism proposed in this document is applicable to
>    both MPLS and IPv6 data planes of SR.
>
>
>
> The IETF datatracker status page for this draft is:
> https://datatracker.ietf.org/doc/draft-ietf-pce-segment-routing-policy-cp/
>
> There are also htmlized versions available at:
> https://tools.ietf.org/html/draft-ietf-pce-segment-routing-policy-cp-01
>
> https://datatracker.ietf.org/doc/html/draft-ietf-pce-segment-routing-policy-cp-01
>
> A diff from the previous version is available at:
>
> https://www.ietf.org/rfcdiff?url2=draft-ietf-pce-segment-routing-policy-cp-01
>
>
> Please note that it may take a couple of minutes from the time of
> submission
> until the htmlized version and diff are available at tools.ietf.org.
>
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>
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