[Lsr] Rtgdir last call review of draft-ietf-ospf-mpls-elc-13

Dhruv Dhody via Datatracker <noreply@ietf.org> Tue, 05 May 2020 09:44 UTC

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Subject: [Lsr] Rtgdir last call review of draft-ietf-ospf-mpls-elc-13
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Reviewer: Dhruv Dhody
Review result: Has Issues

Hello,

I have been selected as the Routing Directorate reviewer for this draft. The
Routing Directorate seeks to review all routing or routing-related drafts as
they pass through IETF last call and IESG review, and sometimes on special
request. The purpose of the review is to provide assistance to the Routing ADs.
For more information about the Routing Directorate, please see
​http://trac.tools.ietf.org/area/rtg/trac/wiki/RtgDir

Although these comments are primarily for the use of the Routing ADs, it would
be helpful if you could consider them along with any other IETF Last Call
comments that you receive, and strive to resolve them through discussion or by
updating the draft.

Document: draft-ietf-ospf-mpls-elc-13
Reviewer: Dhruv Dhody
Review Date: 2020-05-05
IETF LC End Date: 2020-05-05
Intended Status: Proposed Standard

Summary:
I have some minor concerns about this document that I think should be resolved
before publication.

Comments:

Disclaimer: I reviewed an earlier version (-09) as part of the early
directorate review, which could be located at -
https://datatracker.ietf.org/doc/review-ietf-ospf-mpls-elc-09-rtgdir-early-dhody-2019-09-12/

I have reviewed this and the IS-IS I-D together and you will find similar
comments for both I-Ds. You could discuss them in one place.

Major Issues:
None

Minor Issues:
(1) Introduction

   Recently, mechanisms have been defined to signal labels via link-
   state Interior Gateway Protocols (IGP) such as OSPFv2 [RFC8665] and
   OSPFv3 [RFC8666].

   Is there a better way to introduce OSPF extension for SR (than saying that
   it is just an example to signal labels)?

(2) Section 3

    Query: The text says that the ABR "MUST" preserve the ELC setting where as
    the ASBR "SHOULD" preserve it. What is the reason for using SHOULD in case
    of ASBR? Maybe we can spell out in which case ASBR might not preserve the
    ELC setting.

(3) Section 4

   The absence of ERLD-MSD advertisements indicates only that the
   advertising node does not support advertisement of this capability.

   Do you mean to differentiate between support for the capability itself v/s
   support for 'advertisement' only. But RFC 8662 says that ERLD value is
   advertised only when following conditions are met:

   *  MUST be entropy label capable and, as a consequence, MUST apply
      the data-plane procedures defined in [RFC6790].

   *  MUST be able to read an ELI/EL, which is located within its ERLD
      value.

   *  MUST take into account an EL within the first ERLD labels in its
      load-balancing function.

   Thus, I am not sure about this sentence. Maybe you mean to say that the
   absence only indicates that the ERLD-MSD value of the node is unknown (and
   it might still be capable of handling ELI/EL)?

(4) Section 4

    What would be the behavior if an OSPF router receives a ERLD of the node
    but no ELC set for the corresponding prefix? That would be an error as per
    RFC 8662, we should specify how one handles it within OSPF. If it is to
    just ignore the ERLD, we should explicitly say that.

Nits:
(1) Change OSPF Working group to LSR Working group in the metadata (first line
of the I-D)

(2) Abstract - use term LSP instead of tunnel for consistency

   OLD:
   An ingress Label
   Switching Router (LSR) cannot insert ELs for packets going into a
   given Label Switched Path (LSP) unless an egress LSR has indicated
   via signaling that it has the capability to process ELs, referred to
   as the Entropy Label Capability (ELC), on that tunnel.
   NEW:
   An ingress Label
   Switching Router (LSR) cannot insert ELs for packets going into a
   given Label Switched Path (LSP) unless an egress LSR has indicated
   via signaling that it has the capability to process ELs, referred to
   as the Entropy Label Capability (ELC), on that LSP.
   END

(3) Section 4 s/Node MSD sub-TLV/Node MSD TLV/

(4) Expand BGP-LS on first use.

Thanks!
Dhruv