Last Call Review of draft-ietf-isis-mpls-elc-12
review-ietf-isis-mpls-elc-12-rtgdir-lc-dhody-2020-05-05-00

Request Review of draft-ietf-isis-mpls-elc
Requested rev. no specific revision (document currently at 13)
Type Last Call Review
Team Routing Area Directorate (rtgdir)
Deadline 2020-05-05
Requested 2020-04-20
Requested by Alvaro Retana
Authors Xiaohu Xu, Sriganesh Kini, Peter Psenak, Clarence Filsfils, Stephane Litkowski, Matthew Bocci
Draft last updated 2020-05-05
Completed reviews Rtgdir Early review of -08 by Dhruv Dhody (diff)
Rtgdir Last Call review of -12 by Dhruv Dhody (diff)
Opsdir Last Call review of -12 by Scott Bradner (diff)
Secdir Last Call review of -12 by Rich Salz (diff)
Genart Last Call review of -11 by Mohit Sethi (diff)
Assignment Reviewer Dhruv Dhody
State Completed
Review review-ietf-isis-mpls-elc-12-rtgdir-lc-dhody-2020-05-05
Posted at https://mailarchive.ietf.org/arch/msg/rtg-dir/7v_9vrRnGng2SKHptVBhJKFlJ5M
Reviewed rev. 12 (document currently at 13)
Review result Has Issues
Review completed: 2020-05-05

Review
review-ietf-isis-mpls-elc-12-rtgdir-lc-dhody-2020-05-05

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 ‚Äčhttp://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-isis-mpls-elc-12
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 (-08) as part of the early directorate review, which could be located at - https://datatracker.ietf.org/doc/review-ietf-isis-mpls-elc-08-rtgdir-early-dhody-2019-09-12/

I have reviewed this and the OSPF 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 IS-IS [RFC8667]. 

   Is there a better way to introduce IS-IS 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)? 

   I see similar language in RFC8491 but I think we could be clearer in this I-D for ERLD.

(4) Section 4 

    What would be the behavior if an IS-IS router receives an 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 IS-IS. If it is to just ignore the ERLD, we should explicitly say that.  

(5) Section 4

    We need to clearly state that this new MSD Type is carried in Node MSD sub-TLV as described in [RFC8491]. And then I guess we don't really need figure 2? The format is as per RFC 8491!      

Nits:

(1) 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

(2) Expand BGP-LS on first use! 

Thanks! 
Dhruv