[mpls] RtgDir review: draft-ietf-mpls-lsp-ping-reply-mode-simple-03.txt

[Dan Frost <[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-lsp-ping-reply-mode-simple-03.txt
Reviewer: Dan Frost
Review Date: 19 Aug 2015
Intended Status: Standards Track

Summary:

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

This document addresses an important practical limitation affecting the
use of LSP Ping in deployed networks today.  It is for the most part
clearly written and complete, and contains helpful examples.

Major Issues:

No major issues found.

Minor Issues:

- Section 2, last paragraph: "This document adds one Reply Mode value to
describe the reverse LSP, ...".

This document does not appear to add a Reply Mode value, but rather to
modify the semantics of the "Reply via Specified Path (5)" Reply Mode,
as stated at the beginning of Section 3, so this sentence needs
changing.

- Section 3.1, first paragraph: Suggest adding RFC references for
associated LSPs, e.g. RFC 5960 for MPLS-TP.

- Section 3, general comment: This document is changing the semantics of
Reply Mode 5, and in particular changing the case of Mode 5 without a
Reply Path TLV from invalid to valid.  However, the document does not
appear to discuss interoperability issues in networks with a mix of
"old" and "new" LSRs.  This looks like something that should be
addressed explicitly.

- Section 3.1, last paragraph: This paragraph is very confusing and
either needs to be deleted or completely rewritten.  If, as it appears,
it is not changing existing requirements for IP addressing of LSP Ping
packets per RFCs 4379 and 7110, it should just be deleted.

- Section 4.1, preference ordering of reply options: The document
specifies that reply paths are to be preferred according to the order in
which they appear in the Reply Mode Order TLV.  However, it's not clear
from this document and RFC 7110 what the order semantics are of
including a Reply Path TLV with multiple sub-TLVs.  For instance, in
Section 4.1.1's example, FEC X and FEC Y are listed as different return
paths.  If they are different, what is their preference ordering and
where is this defined?

- General comment: It may be valuable for the authors to include a
Manageability Considerations or similar section to provide guidance to
implementors on configuration options, defaults, etc., particularly
given the operational difficulties that led to this document in the
first place.

Nits:

There are a lot (too many to list here) of minor English grammar
problems, such as missing articles, throughout the text.  I would
suggest the editors do a grammatical review pass to clean these up as
much as possible before the RFC Editor stage.

Cheers,
-d