Re: [Teas] RtgDir review: draft-ietf-teas-p2mp-loose-path-reopt-07.txt

"Joel M. Halpern" <> Fri, 09 December 2016 02:02 UTC

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To: "Rakesh Gandhi (rgandhi)" <>, "" <>
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From: "Joel M. Halpern" <>
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Date: Thu, 8 Dec 2016 21:02:01 -0500
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Subject: Re: [Teas] RtgDir review: draft-ietf-teas-p2mp-loose-path-reopt-07.txt
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Those changes address my concerns.  The RFC Production Center Editors 
may choose to discuss the abstract further (it is still a bit longer 
than they usually like), but they may not.  I can live with it as you 

Thank you,

On 12/8/16 8:57 PM, Rakesh Gandhi (rgandhi) wrote:
> Hi Joel,
> Thank you for the detailed review of the document. Please see inline <RG> for replies..
> On 2016-11-23, 4:10 PM, "Joel M. Halpern" <> wrote:
>> 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
>> ​
>> 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-teas-p2mp-loose-path-reopt-07.txt
>> Reviewer: Joel M. Halpern
>> Review Date: 23-November-2016
>> IETF LC End Date: N/A
>> Intended Status: Standards Track
>> Summary: I have some moderate concerns about this document that I think
>> should be resolved before publication is approved.
>> Comments:
>> Major:
>>     The use of SHOULD and MAY in section 4.1 seems to lead to a device
>> which ostensibly supports this document, but does the wrong things.
>>     First, with regard to the SHOULDs, in the absence of any indication
>> as to why it would not do this, it appears that the SHOULD is really
>> "MUST if the device supports this document" which is what MUST in a
>> document actually means.
>>     Section 4.2 first bullet says that a mid-point LSR "SHOULD" check
>> for a preferable P2MP-TE LSP Tree.  But if it doesn't, it is not
>> supporting this document.  As written, it could decide to ignore the
>> message, even though it claims to support this RFC.
>>     Looking at the handling when a preferable P2MP-TE LSP tree is
>> found, according to the document, the LSR MAY send the PathErr response.
>>  My assumption is that if it does not send the PathErr, it MUST
>> propagate the request.  If it does not do either one, the protocol does
>> not function.  It seems likely that if this is really intended to be
>> optional (MAY), the document would be improved my giving implementors
>> some hint as to when it is desirable or undesirable to send the message.
>>     Then in the third bullet, it is only a SHOULD to pass on the
>> request.  Thus, a device which supports this mechanism, but chooses not
>> to pass on the request, is compliant to this document while preventing
>> other devices from properly supporting the mechanism.
> <RG> Ok, how about following text in Section 4.1?
> -----------
> A mid-point LSR that expands loose next-hop(s) for one or more S2L
>    sub-LSP path(s) does the following upon receiving a Path message with
>    the "P2MP-TE Tree Re-evaluation Request" flag set:
>    o  The mid-point LSR MUST check for a preferable P2MP-TE LSP tree by
>       re-evaluating all S2L sub-LSP(s) that are expanded paths of the
>       loose next-hops of the P2MP-TE LSP.
>    o  If a preferable P2MP-TE LSP tree is found, the mid-point LSR MUST
>       send an RSVP PathErr with the Notify error code 25 defined in
>       [RFC3209] and sub-code "Preferable P2MP-TE Tree Exists (value
>       TBA2)" defined in this document to the ingress node.  The mid-
>       point LSR, in turn, SHOULD NOT propagate the "P2MP-TE Tree Re-
>       evaluation Request" flag in the subsequent RSVP Path messages sent
>       downstream for the re-evaluated P2MP-TE LSP.
>    o  If no preferable tree for P2MP-TE LSP can be found, the mid-point
>       LSR that expands loose next-hop(s) for one or more S2L sub-LSP
>       path(s) MUST propagate the request downstream by setting the
>       "P2MP-TE Tree Re-evaluation Request" flag in the LSP_ATTRIBUTES
>       Object of the RSVP Path message.
>    The sending of an RSVP PathErr with the Notify error code and
>    "Preferable P2MP-TE Tree Exists" sub-code to the ingress node
>    notifies the ingress node of the existence of a preferable P2MP-TE
>    LSP tree and upon receiving this PathErr, the ingress node MUST
>    trigger re-optimization of the LSP using the MBB method with a
> different LSP-ID.
> ---------------
>> Minor:
>>     The abstract is much too long.  Much of the content of the abstract
>> belongs in the introduction.  Even teh second paragraph has too much
>> detail for an abstract.
>> Editorial:
>>     In the last paragraph of the introduction, it says that this
>> document "proposes" solutions.  Given we are now in the position of
>> evaluating publication as a Proposed Standard, I would say that this
>> document "defines" solutions.
> <RG> Ok, how about following Abstract?
> ----------
> Re-optimization of a Point-to-Multipoint (P2MP) Traffic Engineered
>    (TE) Label Switched Path (LSP) may be triggered based on the need to
>    re-optimize an individual source-to-leaf (S2L) sub-LSP or a set of
>    S2L sub-LSPs, both using Sub-Group-Based Re-optimization method, or
>    the entire P2MP-TE LSP tree using the Make-Before-Break (MBB) method.
>     This document discusses the application of the existing mechanisms
>    for path re-optimization of loosely routed Point-to-Point (P2P) TE
>    LSPs to the P2MP-TE LSPs, identifies issues in doing so and defines
>    procedures to address them.  When re-optimizing a large number of S2L
>    sub-LSPs in a tree using the Sub-Group-Based Re-optimization method,
>    the S2L sub-LSP descriptor list may need to be semantically
>    fragmented.  This document defines the notion of a fragment
>    identifier to help recipient nodes unambiguously reconstruct the
>    fragmented S2L sub-LSP descriptor list.
> ----------
> Thanks,
> Rakesh (for authors and contributors)