Re: [Pce] PCE SID-algo draft extension

Hi Samuel, WG,

I support the change, i.e., using constraints/metric-type from Flex-algo definition for path computation.

Only based on that, PCE can have more possibility to get algo-SIDs for the computed path, compared to the traditional constraints (such as that contained in LSPA object, Metric object) which may indicate inconsistent constraints with FAD. 

Although, the traditional constraints may also construct a set of constraints that is consistent with the expected content of FAD (assuming we don't consider the subtle differences in the definitions of similar fields between them), PCE, if without any upgrade, has no motivation to translate the computed path to algo-SID list, and more important, the computed path (e.g, an explicit ERO list) may be totally different with flex-algo BE-path (a single ERO), and cause the algo-SID filtering to fail. 

Thus an explicit indication is necessary for PCE to re-use flex-algo BE path for each domain. If this indication is algo-id, traditional constraints is redundant and no useful at least for the reused flex-algo BE path. However, algo-id constraint may also combine with other useful constraints to get more complicated path, such as a TE-path of an NRP created in the flex-algo topology.  We can define processing rules when algo-id constraint and other constraints exist simultaneously.

Regards,

PSF

Original

From: SamuelSidor(ssidor) <ssidor=40cisco.com@dmarc.ietf.org>
To: pce@ietf.org <pce@ietf.org>;
Cc: pce-chairs <pce-chairs@ietf.org>;
Date: 2023年01月10日 18:21
Subject: [Pce] PCE SID-algo draft extension

_______________________________________________
Pce mailing list
Pce@ietf.org
https://www.ietf.org/mailman/listinfo/pce

Hi all,

I would like to get feedback from PCE WG for one extension proposed for existing SID-algo draft (currently expired), which is trying to cover all existing algorithm types as defined in IGP – that includes SPF (algo 0), Strict-SPF (algo 1) and Flex-algo (algo 128-255)

It introduced SID-algo constraint, which currently can be used for filtering SIDs used in path computed by PCE.

To be able to compute inter-domain Flex-algo path, PCE Flex-algo path-computation must be aligned with path-computation done by IGP (Use ASLA attributes, honor FAD lookup priorities,…). This use-case is different one from SID filtering we need to use constraints/metric-type from Flex-algo definition that is bound to SID algo number specified in constraint.

Before we modify the draft, we would like to know if WG has any objection.

Thanks,

Samuel