Re: [RTG-DIR] Rtgdir early review of draft-ietf-idr-segment-routing-te-policy-18

[Ketan Talaulikar <[e-mail]>]

Hi Med,

Thanks for your quick response and once again for your very detailed and
helpful review.

Please check inline below for clarifications.


On Mon, Jul 25, 2022 at 3:24 AM <[e-mail]> wrote:

> Hi Ketan,
>
>
>
> Thanks for taking care for most of the comments. This version looks much
> more better. There are still some few pending points:
>
>
>
> ·       The description of some fields should be elaborated (e.g., “Preference: a 4-octet value.”, “Local IPv4 Address: a 4-octet IPv4 address.”, ...).
>
> KT> If we take the example of Preference in sec 2.4.1. At the start of
that section, there is a reference to sec 2.7 of the SR Policy arch (now
RFC9256) which describes the field. In some of the recent reviews, I've got
the comment to use references rather than repeating them unless necessary.
In this case, there is no processing or validation of the preference value
to be done by BGP and hence only the reference. For the segment types, the
description of the fields is again covered by RFC9256 and we are just using
the reference to them via the matching segment types.


>
>

>    - I still don’t get how a meaning is associated with some field, but
>    then ask the implem to ignore that meaning:
>
>
>
> “Traffic Class (TC), S, and TTL (Total of
>
>       12 bits) are RESERVED and MUST be set to zero and MUST be ignored.”
>

KT> This is the MPLS label encoding format. It is used for both BSID TLV
(from where you have quoted the above text) and the segment types where the
values can actually be set. For BSID, these fields are "reserved" in this
document and future documents can update this behavior.


>
>
>    - The IANA section should include a note asking IANA to update the
>    I-ID (currently used for the early allocation,
>    [draft-previdi-idr-segment-routing-te-policy]) with this document. Having
>    clear instructions recorded in the document will save some cycles with
>    IANA.
>
>
KT> In the IANA section, we use the "This document" convention as a
reference pointer against each code point. My understanding (and this is
what I've seen happen) is that as part of the IANA actions (e.g., after
IESG evaluation is done or during the RFC editor process), the reference is
updated as RFC-to-be... and then finally to RFCXXXX. So I believe it is
clear enough for IANA as also RFC Editor, but I will be happy to update
based on any guidance from the IANA team.

KT> However, if your point was that we need to trigger an IANA action to
update the registries to reflect the WG draft name instead of the
individual one against which the very initial allocations were made, then I
agree. I can check on that. However, I don't believe that requires any
change in the draft.

Thanks,
Ketan


>
>    -
>
>
>
> Cheers,
>
> Med
>
>
>
> *De :* rtg-dir <[e-mail]> *De la part de* Ketan Talaulikar
> *Envoyé :* dimanche 24 juillet 2022 02:26
> *À :* BOUCADAIR Mohamed INNOV/NET <[e-mail]>
> *Cc :* [e-mail];
> [e-mail]; idr@ietf. org <
> [e-mail]>
> *Objet :* Re: [RTG-DIR] Rtgdir early review of
> draft-ietf-idr-segment-routing-te-policy-18
>
>
>
> Hi Med,
>
>
>
> The draft update has just been posted:
> https://datatracker.ietf.org/doc/html/draft-ietf-idr-segment-routing-te-policy-19
>
>
>
> Please let us know if it addresses your comments and if you have any
> further feedback.
>
>
>
> Thanks,
>
> Ketan
>
>
>
>
>
> On Wed, Jul 20, 2022 at 1:56 PM <[e-mail]> wrote:
>
> Hi Ketan,
>
>
>
> Thanks for the follow-up.
>
>
>
> Will monitor when the new version is available and react if I have any
> further comments.
>
>
>
> Cheers,
>
> Med
>
>
>
> *De :* rtg-dir <[e-mail]> *De la part de* Ketan Talaulikar
> *Envoyé :* mardi 19 juillet 2022 19:55
> *À :* BOUCADAIR Mohamed INNOV/NET <[e-mail]>
> *Cc :* [e-mail];
> [e-mail]; idr@ietf. org <
> [e-mail]>
> *Objet :* Re: [RTG-DIR] Rtgdir early review of
> draft-ietf-idr-segment-routing-te-policy-18
>
>
>
> Hi Mohamed,
>
>
>
> Thanks for your very detailed review and helpful suggestions. Please check
> inline below for responses.
>
>
>
> We will post the update once the submission tool reopens.
>
>
>
>
>
> On Fri, Jul 8, 2022 at 6:35 PM Mohamed Boucadair via Datatracker <
> [e-mail]> wrote:
>
> Reviewer: Mohamed Boucadair
> Review result: Has Issues
>
> Document: draft-ietf-idr-segment-routing-te-policy-18
> Reviewer: Mohamed Boucadair
> Review Date: 08/07/2022
> IETF LC End Date: N/A
> Intended Status: Standards Track
>
> I appreciate the effort that was spent to progress this draft since more
> than 6
> years!
>
> Before reviewing the document, I started first by re-reading
> RFC8024/RFC9012
> and reading draft-ietf-spring-segment-routing-policy for establishing the
> context. Overall, the approach documented in
> draft-ietf-idr-segment-routing-te-policy is sound and straightforward.
>
> I didn’t find major concerns from a routing standpoint other than the need
> to
> motivate some few claims (see the detailed review file about RRs, for
> example)
> and the lack of considerations related to the handling of the various
> sub-TLVs
> by intermediate routers (if any).
>
> However, there are a number of generic issues that I would recommend to
> consider (see the detailed review for the full list). All these are
> easy-to-fix
> issues.
>
> # General Comments (in no specific order)
>
> ## Consistency
>
> ### Single or multiple paths
>
> There is an apparent inconsistency in the document about the handling of
> multiple paths. For example, Section 1 says :"Selection of the best
> candidate
> path for an SR Policy" while the same section says also “this will result
> in
> one or more candidate paths being installed into ..”.
>
>
>
> KT> The first is about the selection of the best candidate path for an SR
> Policy by the SRPM - this is what gets installed in the forwarding. The
> second is about the installation of the received candidate paths into the
> BGP table. There is no inconsistency.
>
>
>
>
> If multipath is supported, then please add an explicit statement and make
> sure
> the overall text is consistent.
>
>
>
> KT> Only a single CP is selected for a given SR Policy. This is per the
> draft-ietf-spring-segment-routing-policy and this document does not change
> that.
>
>
>
>
> ### Value 0 is marked as reserved for some registries, while that value is
> associated with a meaning for other registries.
>
> Is there any reason why a consistent approach isn’t followed here? what is
> the
> issues if value 0 is open for assignment?
>
>
>
> KT> It is normal routing protocol practice to not assign the TLV 0 values.
> Can you indicate where the TLV code point 0 is being assigned?
>
>
>
>
> ## Modifications to the format of the Color Extended Community
>
> The text says that you are modifying the format the Color Extended
> Community,
> while this is not true. What this draft does is just associating a meaning
> with
> some bits. I would update the text accordingly.
>
>
>
> KT> We are changing the format of only the Flags field and not of the
> entire EC. Flags are normally independent bits and here we are combining
> two bits to convey 4 values. Clarified this in the Introduction section.
>
>
>
>
> ## Normative language
>
> The use of the normative language should be double-checked. The most
> apparent
> concern is related the statement related to the handling of the reserved
> bits
> (SHOULD) while this RFC9012 uses MUST (which is correct, IMO).
>
>
>
> KT> Ack. I will fix it and change it to MUST.
>
>
>
>
> I tagged many others in the full review, fwiw.
>
> ## Lack of description
>
> Many fields are provided without acceptable description (e.g., “Local IPv4
> Address: a 4-octet IPv4 address.” or “Preference: a 4-octet value” !!).
>
>
>
> KT> These fields are in the context of a sub-TLV. There is text in the
> description of that sub-TLV that provides a reference (e.g., to the
> draft-ietf-spring-segment-routing-policy section or a segment type, etc.)
> There is no need to repeat a detailed description for each field IMO.
>
>
>
>
> Also, some fields are provided with a structure but the text says also that
> these are reserved (e.g., 2.4.2 says “TC, S and TTL (Total of 12 bits) are
> RESERVED”).
>
>
>
> KT> This is the MPLS label field. I am not sure that I follow your concern
> here.
>
>
>
>
> I wonder whether you can add a statement to say that multiple flags can be
> set
> simultaneously unless this is precluded by future flag assignments.
>
>
>
> KT> Not sure that is necessary. In most cases, the bits/flags are
> independent. Where they are not, there is generally text explaining their
> relationship or dependency.
>
>
>
>
> Last, the document does not include the expected behavior of intermediate
> routers (e.g., whether it is allowed or not to alter some fields). I guess,
> they must not touch the content of the attributes but it is better if this
> is
> explicitly mentioned in the text.
>
>
>
> KT> Yes, the contents must not be altered. Will clarify in sec 4.2.4.
>
>
>
>
> ## Reserved vs. Unassigned
>
> Almost all the “reserved” bits in the spec can be assigned in the future. I
> would use “Unassigned” as per RFC8126.
>
>
>
> KT> Ack. Will change in a few places where this has been missed.
>
>
>
>
> FWIW, 8126 says the following:
>
>       Unassigned:  Not currently assigned, and available for assignment
>             via documented procedures.
>
>       Reserved:  Not assigned and not available for assignment.
>             Reserved values are held for special uses, such as to extend
>             the namespace when it becomes exhausted.
>
> ## Deprecated values
>
> The document includes notes about some “deprecated” codepoints. I’m not
> sure
> there is a value in having such notes in the final RFC.
>
>
>
> KT> Yes, there is a need. One is to avoid them being used for any other
> sub-TLV in the future. Two is that there are early implementations out
> there that have some degree of support - even if they are just doing some
> parsing/showing.
>
>
>
>
> ## IANA considerations
>
> ### The document uses a mix of TBD statements (e.g., Section 2.4.3) and
> hard-coded values (early assignments). Not sure what’s was the rationale
> especially that code 20 was assigned but not listed as such.
>
>
>
> KT> Fixed.
>
>
>
>
> ### The IANA actions should be more explicit and ask IANA to update
> existing
> entries. For example, the current registry for code 73 points to
> [draft-previdi-idr-segment-routing-te-policy]. Need to update that entry
> and
> similar ones.
>
>
>
> KT> Have fixed the text. IANA will update "This document" to the RFC
> number before publication. There is no need to keep changing the draft name
> through its lifecycle.
>
>
>
>
> ### The document lists (under IANA section) some values that are
> deprecated.
> The document should be clear whether these codes are available for future
> assignment or not.
>
>
>
> KT> Deprecated means they are not available for assignment by IANA unless
> the IETF changes that via an RFC.
>
>
>
>
> ### Many sub-TLVs have flag bits but not all of them have a registry to
> track
> future flag bit assignments.
>
>
>
> KT> The registries would be added by future documents that start using
> those flags.
>
>
>
>
> ## Manageability considerations
>
> No such considerations are included in the document.
>
>
>
> KT> Will add.
>
>
>
>
> # Detailed review
>
> FWIW, you can find my full review at:
>
> * pdf:
>
> https://github.com/boucadair/IETF-Drafts-Reviews/raw/master/draft-ietf-idr-segment-routing-te-policy-18-rev%20Med.pdf
> * doc:
>
> https://github.com/boucadair/IETF-Drafts-Reviews/raw/master/draft-ietf-idr-segment-routing-te-policy-18-rev%20Med.doc
>
>
>
> KT> This was helpful and have incorporated most of those suggestions.
>
>
>
> Thanks,
>
> Ketan
>
>
>
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