Re: [Pce] Shepherd Review of draft-ietf-pce-segment-routing-policy-cp-14

[Ketan Talaulikar <[e-mail]>]

Hi Dhruv,

I've also posted my review of the document from the POV of consistency with
SR Policy Arch and BGP SR Policy SAFI documents

https://mailarchive.ietf.org/arch/msg/pce/xExbrHXRsC66fGUdy5wtvQlbXc4/

I hope these help improve the document by providing a better overall
context of these very important PCEP extensions for SR.

Thanks,
Ketan


On Sat, Apr 6, 2024 at 7:46 PM Dhruv Dhody <[e-mail]> wrote:

> Hi Mike, Authors,
>
> Please make a new version of the I-D where you handle the following items.
> We can then send the I-D to the IESG.
>
> (1) Please handle Ketan's concern and add the IANA note as he suggested -
> https://mailarchive.ietf.org/arch/msg/pce/ZaYof63GNYdplFUOLo6G6hJlx3c/
>
> (2) A few comments/query got missed, please update or respond if no
> changes are needed...
>
> - Section 5.2, I am unsure about the interaction between the unsetting of
> P-flag (PCEP speaker does not support the TLV) and the default value (128
> when the TLV is not present). Isn't it a bit weird?
> - Section 5.4, Should Oper/Config get a registry for ease of adding new
> flags in future?
>
> (3) Some new comments on checking the diff
>
> - abstract, s/[RFC8231]/RFC 8231/ (no references in abstract)
> - s/ANY/any/
> - RFC 7525 is obsolete by RFC 9325, please update!
>
> (4) I am working on the shepherd writeup -
> https://notes.ietf.org/HziLkaoxS6iYoQ3sOcwk-A?view ; will update in the
> datatracker once you post a new version handling these.
>
> Thanks!
> Dhruv
>
> On Mon, Mar 18, 2024 at 7:40 AM Mike Koldychev <[e-mail]> wrote:
>
>> Hi Dhruv,
>>
>> I've incorporated your changes and all the other comments that I have
>> received so far. Hopefully I didn't miss anything. Version 15 is uploaded.
>> Thanks a lot for your comments and updates!
>>
>> Thanks,
>> Mike.
>>
>> On Saturday, March 9th, 2024 at 8:23 AM, Dhruv Dhody <[e-mail]>
>> wrote:
>>
>> Hi Authors,
>>
>> I have finished the shepherd review of
>> draft-ietf-pce-segment-routing-policy-cp-14. Please handle these comments
>> before we ship this I-D to IESG.
>>
>> ## Major
>> - Section 5.6, you need to add update: RFC 8231 in the draft metadata.
>> This should also be captured in the abstract. The prefered way is to
>> clearly identify the text in RFC8231 that is changing with "OLD:" and
>> "NEW:" format!
>> - Section 8, Security considerations need to also cover the non-SRPA TLVs
>> which are not considered in the current text.
>>
>> ## Query
>> - Section 4.1,
>> ````
>> If the PCC receives a
>> PCInit message with the Association Source set not to the headend IP
>> but to some globally unique IP address that the headend owns, then
>> the PCC SHOULD accept the PCInit message and create the SRPA with the
>> Association Source that was sent in the PCInit message.
>> ````
>> What is the purpose of this text? PCC should use the source as set by the
>> PCE - isn't it given? Am I missing something? Boris also pointed this out
>> in his review.
>>
>>
>> ## Minor
>> - Abstract is not very useful for a non-expert. Maybe change something
>> like -
>> ````
>> OLD:
>> A Segment Routing (SR) Policy is a non-empty set of SR Candidate
>> Paths, which share the same <headend, color, endpoint> tuple. SR
>> Policy is modeled in PCEP as an Association of one or more SR
>> Candidate Paths. PCEP extensions are defined to signal additional
>> attributes of an SR Policy. The mechanism is applicable to all SR
>> forwarding planes (MPLS, SRv6, etc.).
>> NEW:
>> Segment Routing (SR) allows a node to steer a packet flow along any
>> path. SR Policy is an ordered list of segments (i.e.,
>> instructions) that represent a source-routed policy. Packet flows
>> are steered into an SR Policy on a node where it is instantiated
>> called a headend node. An SR Policy is made of one or more candidate
>> paths.
>>
>> This document specifies Path Computation Element Communication
>> Protocol (PCEP) extension to associate candidate paths of the SR
>> Policy. It applies equally to the SR-MPLS and Segment Routing over
>> IPv6 (SRv6) instantiations of segment routing.
>> END
>> ````
>> - Similarly I find Introduction to be very light on details. Consider
>> adding text by looking through recently published RFCs for instance.
>> - Terminology:
>> ```
>> OLD:
>> SRPA: SR Policy Association. PCEP ASSOCATION that describes the SR
>> Policy. Depending on discussion context, it refers to a PCEP
>> object or to a group of LSPs that belong to the Association.
>> NEW:
>> SRPA: SR Policy Association. A new association type 'SR Policy
>> Association' is used to group candidate paths belonging to the SR
>> Policy. Depending on discussion context, it can refer to the PCEP
>> ASSOCIATION object of SR Policy type or to a group of LSPs that
>> belong to the association.
>> END
>> ```
>> - Section 4, please add this text at the start -
>> ````
>> As per [RFC8697], LSPs are associated with other LSPs with which they
>> interact by adding them to a common association group. As described
>> in [RFC8697], the association group is uniquely identified by the
>> combination of the following fields in the ASSOCIATION object:
>> Association Type, Association ID, Association Source, and (if
>> present) Global Association Source or Extended Association ID,
>> referred to as Association Parameters.
>> ````
>> - Section 4.2, since none of the TLV are multi-instance. Can we simplify
>> this text -
>> ````
>> OLD:
>> Unless specifically stated otherwise, the TLVs listed in the
>> following sub-sections are assumed to be single instance. Meaning,
>> only one instance of the TLV SHOULD be present in the object and only
>> the first instance of the TLV SHOULD be interpreted and subsequent
>> instances SHOULD be ignored.
>> NEW:
>> This document specifies four new TLVs to be carried in the SRPA object.
>> Only one TLV instance of each type can be carried, and only the first
>> occurrence is processed. Any others MUST be ignored.
>> ````
>> Also applicable to section 5!
>> - Section 4.2.2, consider changing the SHOULD to MUST in this section. I
>> could not think of a justification for SHOULD here!
>> - Section 5.1,
>> - please also state what happens if the TLVs are used without the
>> exchange of SRPOLICY-CAPABILITY TLV or the corresponding bit is unset.
>> Without it, what is the use of adding this TLV?
>> - Consider updating the description such as "P-flag: If set to '1' by a
>> PCEP speaker, the P flag indicates that the PCEP speaker supports the
>> handling of COMPUTATION-PRIORITY TLV for the SR Policy."
>> - please add "Unassigned bits MUST be set to '0' on transmission and MUST
>> be ignored on receipt."
>> - Section 5.2, I am unsure about the interaction between the unsetting of
>> P-flag (PCEP speaker does not support the TLV) and the default value (128
>> when the TLV is not present). Isn't it a bit weird?
>> - Section 5.3, should the use of this TLV be limited to SR-MPLS? Also can
>> ENLP value be converted into a registery maintained at
>> https://www.iana.org/assignments/segment-routing/segment-routing.xhtml
>> which can be referred by both PCE and BGP?
>> - Section 5.4, please add "The unassigned bits in the Flag octet MUST be
>> set to zero upon transmission and MUST be ignored upon receipt." Should
>> "Invalidation Reasons Flags" get a registry for ease of adding new flags in
>> future? In general, can the text in this section be tightened a little bit?
>> Examples - be explicit on who is sending and who is receiving for instance.
>> Also, consider adding a more detailed example to show the usage of the
>> flags better alongside PCEP message exchange.
>> - Section 5.5, please add normative reference to
>> draft-ietf-pce-binding-label-sid
>> - Section 6.5, are you refereing to the registry at
>> https://www.iana.org/assignments/segment-routing/segment-routing.xhtml,
>> in which case it is called "Segment Routing" and not "Segment Routing
>> Parameters". Also better to call the new registry being added as
>> subregistry.
>> - Section 10.2, please make RFC 8253 and RFC 7525 as normative
>> references.
>>
>> ## Nits
>> - Expand PCEP and SR in the title
>> - Expand PCEP, SRv6 in the abstract
>> - Expand MBZ on first use. It is also better to state that the field is
>> ignored on receipt
>> - Section 4.2.2, add reference to RFC 9256 for Discriminator, as you have
>> done for other fields
>> - Section 4.2.4, add reference to RFC 9356 for Preference
>> - s/there needs to be a separate capability negotiation/a separate
>> capability negotiation is useful/
>> - Expand on first use OAM/PM/BFD
>> - Section 6, please update the text in subsections where the number of
>> assignments in tables do not match the introductory text.
>>
>> I am also attaching the updated xml that could be a starting point for
>> you to work on -15 version.
>>
>> Thanks!
>> Dhruv
>>
>>
>>