[RTG-DIR] RtgDir review: draft-ietf-mpls-spring-entropy-label

[Daniele Ceccarelli <[e-mail]>]

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-mpls-spring-entropy-label

Reviewer: Daniele Ceccarelli

Review Date: 2018/02/20

IETF LC End Date: date-if-known

Intended Status: Informational



Summary:

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

Comments:



The document is well written and I really appreciated the detailed examples and the analysis of the options described in section 10. My only concern, in addition the minor issues listed below, is the scope of the document. It is an informational document and the abstract says it examines and describes how Els are applicable to segment routing. Reading the text it seems it is much more. There are requirements and procedures describer in the document as well as requirements and RFC2119 language is often used. Maybe it’s worth considering a better scoping of the document?



Major Issues:

None



Minor Issues:

  *   Introduction: “Entropy label (EL) [RFC6790] is a technique used in the MPLS data plane to provide entropy for load-balancing.” Providing an intro on what an EL is can be very useful, but a bit more or explanation is needed, just a couple of sentences.
  *   Section 1.1 – Is this needed? The abstract says “This document examines and describes how ELs are to be applied to Segment Routing” and the status is informational. I’m not sure RFC2119 language is needed. E.g. in section 4 “A router capable of reading N labels but not using an EL located within those N labels MUST consider its ERLD to be 0”.  Further reading the document I see constraint against e.g. the ERLD are defined. Maybe it is more appropriate to say that the document also describes the requirements for the usage of EL in SPRING MPLS ? Moreover in section 6 it seems to describe procedures, so it’s even more than applicability and requirements.
  *   Section 3: I don’t understand what this sentence means. Can you rephrase? “As each MPLS node may have limitations in the number of labels it can push when it is ingress or inspect when doing load-balancing, an entropy label insertion strategy becomes important to keep the benefit of the load-balancing.



Nits:

- Abstract: suggest avoid repetition of “applied” as well as examines and describes. What about: “This document describes how Els can be  applied to Segment Routing with an MPLS data plane.

- Section 6: “In term of packet forwarding, by learning the mapping-server advertisement from PE5,”…it should be P5 not PE5.

- Section 6: “   To accomodate the mix of signalling protocols involved during the

   stitching, the entropy label capability SHOULD be propagated between the signalling protocols.” Not clear what this means, maybe it should be propagated between the two domains, not the signaling protocols?



Thanks,

Daniele