Re: [Lsr] Working Group Last Call for "Flexible Algorithms: Bandwidth, Delay, Metrics and Constraints" - draft-ietf-lsr-flex-algo-bw-con-07

Co-Authors, 

I believe these are the only pending WG last comments. 

Thanks,
Acee

> On Mar 21, 2024, at 12:36 PM, Ketan Talaulikar <ketant.ietf@gmail.com> wrote:
> 
> Hi All,
> 
> I have reviewed this document and believe it needs some further work before publication. 
> 
> I am sharing my comments below: 
> 
> 1) There is the following text in sec 2.1 and 2.2 for Generic Metric.
> 
> A metric value of 0xFFFFFF is considered as maximum link metric and a link having this metric value MUST NOT be used during Flex-algorithm calculations [RFC9350]. The link with maximum generic metric value is not available for the use of Flexible Algorithms but is availble for other use cases.
> 
> I believe the FlexAlgo reference here is to https://www.rfc-editor.org/rfc/rfc9350.html#name-max-metric-consideration 
> But the above text does not align with the RFC9350. If a link is to be made unavailable for FlexAlgos operating with a specific Generic Metric, then the way to do that is to omit that specific Generic Metric TLV from the ASLA for flex-algo application. The same would apply for other applications - just omit the metric. Why do we need a special MAX-LINK-METRIC value for generic metric given that it is a new thing we are introducing?
> 
> 2) This comment is specific to OSPF given the encoding differences it has with ISIS. Section 2.2 allows for Generic Metric TLV to be used in too many places without clear specification of what it is used for - this is a potential pitfall for interop issues. RFC9492 provides helpful directions for us here.
> a) This draft specifies FlexAlgo extensions, it is natural that Generic Metric be advertised under ASLA TLV. No issues here.
> b) This draft does not specify anything about use of generic metric in base OSPF and as a reminder there is nothing like L-bit in OSPF encoding. Therefore, it does not make sense to advertise Generic Metric outside of ASLA and under the OSPFv2 Extended Link TLV or OSPFv3 Router Link TLV.
> c) This draft does not specify anything about use of generic metric with RSVP-TE/GMPLS. Therefore, it does not make sense to advertise Generic Metric in the TE Opaque LSAs.
> We can have specific documents that introduce (b) or (c) when there is a proper specification.
> 
> 3) Please introduce a reserved field to pad the OSPF FAEMD sub-TLV to a 4 octet boundary as is the convention in OSPF - https://www.ietf.org/archive/id/draft-ietf-lsr-flex-algo-bw-con-08.html#section-3.2.2
> 
> 4) In section 3.2.2 there is the following text for OSPF. Could you please use the TLV/sub-TLV name? OSPF folks are not good at remembering numbers ;-)
> 
> The Min Unidirectional Link Delay as advertised by sub-sub-TLV 12 of ASLA sub-TLV [RFC8920], MUST be compared against the Maximum delay advertised in the FAEMD sub-TLV. 
> 
> 5) Do we want to call out that the reference bandwidth approach requires a router to compute and maintain a per link per algo bandwidth metric for every link in that algo topology. It may not be very obvious to some.
> 
> 6) There are a lot of procedures which are common to both OSPF and ISIS and are repeated in each section instead of a common section. It would be easier (and avoid errors) if there was some consolidation. https://www.rfc-editor.org/rfc/rfc9350.html#section-5 provides a good reference for such an organization of text.
> 
> 7) Regarding https://www.ietf.org/archive/id/draft-ietf-lsr-flex-algo-bw-con-08.html#section-6, it seems like we want to retain a numbering ordering of rules/sequence for flex-algo as extension documents are introduced. Am I correct? If so, then this document should formally "update" RFC9350 since it is changing the "set of rules/sequence" for FlexAlgo computations. Further such extensions will also need to keep updating the base spec similarly. I would suggest that a full set of rules that is a union of what is in RFC9350 and rules added by this draft are maintained in an Appendix section. Other documents in the future can similarly maintain the latest set of rules.
> 
> 8) Please fix idnits warnings - some are related to obsolete references while others are related to formatting. There are also some spelling/grammar errors.
> 
> Thanks,
> Ketan
> 
> 
> On Tue, Feb 20, 2024 at 3:56 AM Acee Lindem <acee.lindem@gmail.com> wrote:
> 
> This starts the Working Group Last call for draft-ietf-lsr-flex-algo-bw-con-07. At least some of the flex algorithm enhancements described in the document have been implemented. 
> 
>  Please send your support or objection to this before March 5th, 2024. 
> 
> Thanks,
> Acee
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