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

From: Dan Frost <[email-masked]>
Date: Wed, 19 Aug 2015 17:49:52 +0100

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

---

From: Nobo Akiya <[email-masked]>
Date: Sun, 30 Aug 2015 17:19:34 +0900

Hi Dan,

Thanks for reviewing this document!

Please see replies in-line with [NOBO].

> as stated at the beginning of Section 3, so this sentence needs

[NOBO] Thanks for catching that ... left over from previous proposal. I
have updated to:

      This document updates the "Reply via Specified Path (5)" Reply Mode
      to easily indicate the reverse the reverse LSP, and adds one optional
      TLV to describe an ordered list of reply modes.

> associated LSPs, e.g. RFC 5960 for MPLS-TP.

[NOBO] Yes that will be helpful to readers, added.

> "old" and "new" LSRs.  This looks like something that should be
[NOBO] Good point. I have added a new sub-section to clarify this.

4.1.  Backwards Compatibility with Reply via Specified Path (5) Reply
      Mode

   [RFC7110] has introduced the "Reply via Specified path (5)" Reply
   Mode, and defined that usage of the "Reply via Specified path (5)"
   Reply Mode without also including the "Reply Path TLV" to be invalid.
   This document relaxes this semantic by defining the use of the "Reply
   via Specified path (5)" Reply Mode without the "Reply via Specified
   path (5)" to indicate the reverse LSP.  In other words, what was
   considered invalid is now valid.  If the initiator LSR, which sent an
   MPLS echo request message with the "Reply via Specified path (5)"
   Reply Mode but without including the "Reply Path TLV", receives back
   an MPLS echo reply message with the return code being "Malformed echo
   request received", then the initiator LSR SHOULD assume that the
   responder LSR does not support the mechanism defined in this document.

> packets per RFCs 4379 and 7110, it should just be deleted.
[NOBO] I believe this text was suggested by someone to be added, but since
this is already described in RFC 7110, I will delete it as suggested.

> paths.  If they are different, what is their preference ordering and

[NOBO] That should have been clarified in the RFC 7110, but unfortunately
not. Folks, including myself, assumed that selection is done via walking
the Sub-TLVs from "top to bottom". Do you suggest that we attempt to
clarify this in this document?

> given the operational difficulties that led to this document in the

[NOBO] Good point. I have a Manageability Considerations section.

   Section 2 described the problems which increases the complexity with
   respect to operations and implementations.  In order to to simplify
   operations and to allow for the LSP Ping/Traceroute to function
   efficiently whilst preserving the code simplicity, it is RECOMMENDED
   that implementations allow devices to have configuration options to
   set operator preferred Reply Modes.  For example:

   o  For those operators who are more interested in MPLS echo reply
      packets reaching back to the initiator LSR:

      1.  Reply via an IPv4/IPv6 UDP packet (2)

      2.  Reply via application level control channel (4)

      3.  Reply via Specified Path (5)

   o  For those operators who are more interested in MPLS echo reply
      packets testing the paths related to the forward LSP:

      1.  Reply via Specified Path (5)

      2.  Reply via application level control channel (4)

      3.  Reply via an IPv4/IPv6 UDP packet (2)

> much as possible before the RFC Editor stage.

[NOBO] I will have one of the native English speaker do a cleanup.

Again, thanks for reviewing the document Dan. Please let me know what you
would like for the Sub-TLV preference within the Reply Path TLV ... which
is really an issue with RFC 7110.

Regards,
Nobo

>
> Cheers,
> -d
>
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