Re: [mpls] 2nd WG LC on draft-ietf-mpls-bfd-directed

"Carlos Pignataro (cpignata)" <> Sat, 20 August 2016 05:22 UTC

Return-Path: <>
Received: from localhost (localhost []) by (Postfix) with ESMTP id ABF0D12D1C8; Fri, 19 Aug 2016 22:22:11 -0700 (PDT)
X-Virus-Scanned: amavisd-new at
X-Spam-Flag: NO
X-Spam-Score: -15.767
X-Spam-Status: No, score=-15.767 tagged_above=-999 required=5 tests=[BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, HTML_MESSAGE=0.001, RCVD_IN_DNSWL_HI=-5, RCVD_IN_MSPIKE_H3=-0.01, RCVD_IN_MSPIKE_WL=-0.01, RP_MATCHES_RCVD=-1.247, SPF_PASS=-0.001, USER_IN_DEF_DKIM_WL=-7.5] autolearn=ham autolearn_force=no
Authentication-Results: (amavisd-new); dkim=pass (1024-bit key)
Received: from ([]) by localhost ( []) (amavisd-new, port 10024) with ESMTP id fWK2E-7b-97m; Fri, 19 Aug 2016 22:22:07 -0700 (PDT)
Received: from ( []) (using TLSv1.2 with cipher DHE-RSA-SEED-SHA (128/128 bits)) (No client certificate requested) by (Postfix) with ESMTPS id 8F23812B034; Fri, 19 Aug 2016 22:22:06 -0700 (PDT)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple;;; l=217446; q=dns/txt; s=iport; t=1471670526; x=1472880126; h=from:to:cc:subject:date:message-id:references: in-reply-to:mime-version; bh=qvDo8B/EndD/aLu1AuJPmYzXTDIaRlkA45JMpDjfXzk=; b=MK0k2KCpfDGqZ0p4iAUFFVmbyvAPpeUO8tZ1weHFATy4uUBTixleVmqZ VA95e+1Nzr2rlAMQ4HIVIquw43GE7/weV/8Q1WinqDjTGKldg1s9DEO4d dDfN6ye5qfOfWgiKUCBKkMA2mgcgRyeu5wMpSkXGEcKYql0xvqfDu+cT1 E=;
X-IronPort-Anti-Spam-Filtered: true
X-IronPort-Anti-Spam-Result: =?us-ascii?q?A0B6AgDQ6LdX/5hdJa1egnZOVnwHgnq0c?= =?us-ascii?q?oF9JoRngRACHIFKOBQCAQEBAQEBAV4nhF4BAQUBAQoOAQgERwsQAgEGAhEEAQE?= =?us-ascii?q?hAQYDAgICJQsUCQgCBA4FG4gWDgONZZ0ij3QBAQEBAQEBAQEBAQEBAQEBAQEBA?= =?us-ascii?q?QEXBYYrgXgIgUqBA4QSCgEFAgEyH4JLK4IvBYgfi2KFRwGGH4h/gW2EXIMzhVS?= =?us-ascii?q?GaRqFPIN3AR42ghIcgUxwAYVoAQEkBAMZfwEBAQ?=
X-IronPort-AV: E=Sophos;i="5.28,548,1464652800"; d="scan'208,217";a="313203222"
Received: from ([]) by with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 20 Aug 2016 05:21:56 +0000
Received: from ( []) by (8.14.5/8.14.5) with ESMTP id u7K5Luje025003 (version=TLSv1/SSLv3 cipher=AES256-SHA bits=256 verify=FAIL); Sat, 20 Aug 2016 05:21:56 GMT
Received: from ( by ( with Microsoft SMTP Server (TLS) id 15.0.1210.3; Sat, 20 Aug 2016 01:21:55 -0400
Received: from ([]) by ([]) with mapi id 15.00.1210.000; Sat, 20 Aug 2016 01:21:55 -0400
From: "Carlos Pignataro (cpignata)" <>
To: Eric Gray <>
Thread-Topic: [mpls] 2nd WG LC on draft-ietf-mpls-bfd-directed
Date: Sat, 20 Aug 2016 05:21:55 +0000
Message-ID: <>
References: <> <> <> <> <> <> <> <> <> <07f401d1f938$a13eb060$e3bc1120$> <>
In-Reply-To: <>
Accept-Language: en-US
Content-Language: en-US
x-ms-exchange-messagesentrepresentingtype: 1
x-ms-exchange-transport-fromentityheader: Hosted
x-originating-ip: []
Content-Type: multipart/alternative; boundary="_000_DB818082086540648BAF340070B44E8Aciscocom_"
MIME-Version: 1.0
Archived-At: <>
Cc: "" <>, "" <>, mpls <>
Subject: Re: [mpls] 2nd WG LC on draft-ietf-mpls-bfd-directed
X-Mailman-Version: 2.1.17
Precedence: list
List-Id: Multi-Protocol Label Switching WG <>
List-Unsubscribe: <>, <>
List-Archive: <>
List-Post: <>
List-Help: <>
List-Subscribe: <>, <>
X-List-Received-Date: Sat, 20 Aug 2016 05:22:11 -0000


On Aug 19, 2016, at 3:02 PM, Eric Gray <<>> wrote:

Hi Adrian,

                Correct me if I am wrong, but aren’t you fudging the distinction between WG Adoption and WG Last Call just a bit?

                My understanding is that WG adoption is intended to determine if the WG supports developing a specific proposed solution, and WG Last Call is more about whether or not the WG  believes the solution is complete and not in conflict with other work in the WG.

                Usually, we should expect that the direction a draft is supposed to be headed is determined well before last call, hence it is reasonable to suppose that a minority arguing to take a different approach are somewhat out of line.

                Agreed, if the WG has – for whatever reason – substantially changed its collective opinion since adoption and feels the solution is no longer supportable, then WG Last Call is pretty much the last available time to establish this.  But I suspect the bar for establishing that this is the current WG rough consensus needs to be pretty high (more than a relatively small number of dissenters) or we will be setting ourselves up for doing even more work that somehow never leads to any sort of satisfactory conclusion.

                Do you think this is the point we are at?

                On the quasi-technical issue you’re making (or supporting), I think there is some confusion.  RFC 7710 is probably not the RFC you meant to refer to; RFC 7710 is “Captive-Portal Identification Using DHCP or Router Advertisements (RAs)” and does not mention BFD at all.

                Possibly you meant to refer instead to RFC 7110, as this draft does?

                In any case, there are a few language issues in this discussion.  There is a difference between “BFD is also expected to monitor unidirectional paths” (which MAY be true) and “BFD MAY also be used to monitor unidirectional paths” (which ISmostly true).  And I think people should take some minor exception to your wording that “BFD is designed to monitor unidirectional and bidirectional paths” since the “B” has a pretty much unambiguous meaning.  It is clear that BFD may be capable of monitoring a unidirectional path – assuming that some sort of reverse path exist and may practically be used for this purpose (which – in spite of the fact that this is the most common case – is not necessarily true).

                Specifically, though I would not expect a revision just to address this, I find the current wording (based on your comments below) a little misleading, because now it says “Bidirectional Forwarding Detection (BFD) is expected to monitor any kind of paths between systems.”  This is pretty much what your comment implies, but is clearly not true (from an English language perspective) because any such expectation clearly will not scale (there are a great many systems with a great many more paths between them, hence expecting BFD to monitor any kind of path between systems is setting our expectations a little high).  This is the difference between expecting <protocol X> to do <Y> and expecting <protocol X> to be able to do <Y>.

You seem to take exception with the language “any kind of paths between systems” (based on the added emphasis).

When a document is talking about a previously specified protocol, I always find the safest path to go and look up and read the actual specification of said protocol. In this case we are talking about BFD.
“   BFD can provide failure detection on any kind of path between
“   The Bidirectional Forwarding Detection (BFD) protocol [BFD] defines a
   method for liveness detection of arbitrary paths between systems."

A citation is worth many paragraphs :-)


— Carlos.

                In addition to not scaling, because there are scenarios in which a practical usable reverse path may not exist, this statement is not actually true even if re-phrased as “BFD may be used to monitor any kind of path between systems.”  As an example of a case where this is clearly not true in any practical sense, it would – from a practical and feasibility perspective – probably be a poor idea to monitor Satellite Television reception (for the path from satellite to however many Television receivers) using BFD.


From: mpls [] On Behalf Of Adrian Farrel
Sent: Thursday, August 18, 2016 6:10 AM
To: Gregory Mirsky <<>>; 'Carlos Pignataro (cpignata)' <<>>
Cc: 'mpls' <<>>;<>;<>
Subject: Re: [mpls] 2nd WG LC on draft-ietf-mpls-bfd-directed


I'm disappointed by the last sentence of your email. This a WG last call: its purpose is to determine whether the WG supports the proposed solution. IIRC the reason for this second WG last call is that the WG chairs were unable to determine consensus from the first call.

I'm sure it isn't your intention, but your email appears to read, "Let's not debate the problem and direction of the solution because they are not up for discussion."

Obviously you and Carlos have a disagreement about the need for this work and the way the requirements are expressed. Personally, I've got lost in the details of your discussion (not helped by the way the HTML mail presents, below). I suspect that a lot of the problem is around scoping of the problem because RFC 7710 was generally welcomed by the WG, and the fundamentals are surely not so different (although maybe I'm wrong since the IPR disclosures are different).

I also suspect that there are some linguistic confusions between the two of you. Sometimes this can be mitigated by rephrasing and using more words. As a case in point, Carlos originally objected to "Bidirectional Forwarding Detection (BFD) is expected to monitor bi-directional paths," noting that, "BFD also is expected to monitor unidirectional paths." The two statements are not actually contradictory and one could say (without damaging the value of the document), "BFD is designed to monitor unidirectional and bidirectional paths."

In fact, as we discovered while working on RFC 7710, the false negative may result precisely from using the reverse (co-routed or not) path. So the value of controlling the return path is to help diagnose whether the fault is on the outbound path or the return path, and this applies equally to unidirectional paths and bidirectional paths.


From: mpls [] On Behalf Of Gregory Mirsky
Sent: 17 August 2016 23:19
To: Carlos Pignataro (cpignata)
Cc:<>; mpls;<>
Subject: Re: [mpls] 2nd WG LC on draft-ietf-mpls-bfd-directed

Hi Carlos,
I believe that new version of the draft addresses all technical comments and now are discussing what each of us believes and how we interpret this or that IETF document. While this is very enlightening and I enjoy this discussion very much I don’t see that I can change how you see the problem this proposal addresses. The MPLS WG had agreed that the problem is real and the proposed solution, within the scope defined, is technically sound.


From: Carlos Pignataro (cpignata) []
Sent: Tuesday, August 16, 2016 10:02 AM
To: Gregory Mirsky <<>>
Cc: Martin Vigoureux <<>>; mpls <<>>;<>;<>
Subject: Re: [mpls] 2nd WG LC on draft-ietf-mpls-bfd-directed

Hi, Greg,

I think we got to the source of the technical disagreement. Please find some closing comments inline.

On Aug 16, 2016, at 12:22 PM, Gregory Mirsky <<>> wrote:

Hi Carlos,
thank you for clarification of your concerns. Please find my notes in-line and tagged GIM3>>.


From: Carlos Pignataro (cpignata) []
Sent: Tuesday, August 16, 2016 6:14 AM
To: Gregory Mirsky <<>>
Cc: Martin Vigoureux <<>>; mpls <<>>;<>;<>
Subject: Re: [mpls] 2nd WG LC on draft-ietf-mpls-bfd-directed

Hi, Greg,

Thank you for the follow-ups. Let me explain a couple of the key concerns top-posting, with more responses inline.

One of the main technical concerns that I have is that segment routing being a loosely source-routed paradigm, there may not even be a bidirectional co-routed path.
GIM3>> I don’t think that your characterization of the Segment Routing as mandating use only loosely source-routed paths is entirely accurate. As in RSVP-TE, source-routed paths may be loosely or strictly source-routed. Excluding option to construct strictly source-routed paths, in my opinion, would significantly limit scope of the Source Routing technology.

Take the extreme case of a stack in the forward direction with a single Node SID, PE to PE, and shortest path in-between. Or the case of Parallel Link SIDs with varied weights in different links. How are you providing a return path?
GIM3>> Authors do not claim that the proposed solution applies to all scenarios there could be in source routing. I think that has been already clarified in the text and in our discussion.

Conversely, this potentially seems to apply to a grossly small and limited set of scenarios, if any, yet those scenarios are not discussed in the document, and are not defined to my knowledge in any SPRING document — other than a mention in RFC 7855 of:

   It is obvious that, in the case of long, strict source-routed paths,
   the deployment is possible if the head-end of the explicit path
   supports the instantiation of long explicit paths.

which seems to refer to Node strictness and not necessarily Link strictness, and there is nothing in draft-ietf-spring-segment-routing-09.

Can you please point to a definition of a co-routed path for Segment Routing from the segment routing architectural documents?
GIM3>> The proposal does not use bi-directional co-routed Segment Routed tunnels as such construct doesn’t yet exists (though in earlier discussions there was some interest in investigating use case for it). On the other hand, definition of co-routedness can be found in MPLS-TP as “co-routed, meaning both directions follow the same path, i.e. traversing the same set of nodes and links”.

There’s no mention of MPLS-TP or SPRING-TP in SPRING docs either that I could find.

If a SPRING stack includes a long set of Node SIDs, each one for each hop, still multiple-links between nodes are not specified and therefore it is not clear how to provide the exact return path (when the link taken is unknown). If the problem space is limited to the case in which for each hop, both Node SID and Adj SID are included, no Anycast, no Parallel Link SID, etc., then practicality seems to get in the way.

The second main concerns has to do with the proposed use of Labels (which can change) instead of FECs (like RFC 7110).
GIM3>> Authors believe that this is workable solution and the return path for the BFD session identified by BFD Discriminator TLV may be re-signaled without affecting state of the session.

There could perhaps be a use of specifying a return path in this case. However, I believe the use is not the scenario targeted, and it is not specifying data plane labels numerically.

These two seem to be major technical obstacles to the draft.

Please note there were some additional comments inline, but centered around the same set of topics.


— Carlos.

On Aug 10, 2016, at 3:34 PM, Gregory Mirsky <<>> wrote:

Hi Carlos,
thank you for your comments. I hope I understand your concerns better and am able to address them. Please find my follow up notes in-line tagged GIM2>>.


From: Carlos Pignataro (cpignata) []
Sent: Tuesday, August 09, 2016 9:14 PM
To: Gregory Mirsky <<>>
Cc: Martin Vigoureux <<>>; mpls <<>>;<>;<>
Subject: Re: [mpls] 2nd WG LC on draft-ietf-mpls-bfd-directed

Hi Greg,

Thanks for the response — please find some follow-ups inline.

On Jul 25, 2016, at 5:06 PM, Gregory Mirsky <<>> wrote:

Hi Carlos,
thank you for your comments. Please see my responses in-line and tagged GIM>>.


From: mpls [] On Behalf Of Carlos Pignataro (cpignata)
Sent: Saturday, July 16, 2016 8:35 AM
To: Martin Vigoureux <<>>
Cc: mpls <<>>;<>;<>
Subject: Re: [mpls] 2nd WG LC on draft-ietf-mpls-bfd-directed

Hi, Martin,

Admittedly, I had not read or followed this document before. However, I just scanned through it, and I Have at best some fundamental questions and likely some major issues and concerns. I wonder also if you need to Cc the BFD WG, copying the chairs on this response. Copying also SPRING chairs for awareness.

I hope these are useful to this WGLC.

Major Concerns:

As I said, I just glanced through the document, and found these issues, questions, or problems.

1. Motivation for the work.

Uni or bi-directional? The document starts with a fallacy, setting the tone for the document, on the very first sentence:


   Bidirectional Forwarding Detection (BFD) is expected to monitor bi-
   directional paths.

This is absolutely not the case, as explained in RFC 5880 Section 2, RFC 5883 Section 4.3 (, and many other places.
GIM>> I think that you refer to the following text in RFC 5880:

Not specifically, not only.

My point is that the very first sentence contradicts standards tracks BFD RFCs. BFD also is expected to monitor unidirectional paths.

GIM2>> Would the following change address your concern:
Bidirectional Forwarding Detection (BFD) is expected to monitor bi- directional paths. When a BFD session monitors an explicit routed    path there is a need to be able to direct egress BFD peer to use specific path for the reverse direction of the BFD session.
Bidirectional Forwarding Detection (BFD) is expected to monitor any kind of paths between systems. When a BFD session monitors an explicitly routed uni-directional path there may be a need to direct egress BFD peer to use specific path for the reverse direction of the BFD session.

Since segment routing uses a loose source-routing paradigm, there may not be explicitly routed or a reverse direction.

   BFD can provide failure detection on any kind of path between
   systems, including direct physical links, virtual circuits, tunnels,
   MPLS Label Switched Paths (LSPs), multihop routed paths, and
   unidirectional links (so long as there is some return path, of
And this is exactly what motivated the work we’re discussing. Consider the situation when the return path, though temporarily, is not available. Consider scenario when node A sends BFD control packets over an LSP to node B and the node B sends its BFD packets over out of band return path, e.g. IP network.  If the loss of continuity between B and A lasts long enough to will detect failure. Should such failure be interpreted as indication of the failure on the monitored LSP or not?

But this is irrespective of wether the return path is explicit or not, or even if the return path is via some out of band channel. A different way, this is also the case for BFD multihop over plain IP (on a tunnel one way, hop-by-hop routed on the return).

GIM2>> True, but we’re not solving these other scenarios, only those where monitored path is explicitly routed. We can add explicit statement listing out of the scope scenarios.

See above.

The second paragraph in the Introduction section explains the scenario when an explicitly routed LSP being monitored while the return path is over IP network that is based the shortest path paradigm.

The fact that the return path goes over the same links as the forward path does not mean that the return path is misprogrammed but the forward path is correctly programmed.
GIM2>> The purpose of making BFD session use co-routed path is not to verify how it is instantiated in LFIB on a LSR. That is the task for defect localization, not defect detection OAM. Would you agree?

I still believe that the motivation and use case is not well defined or explained.

GIM2>> I’ll keep trying.

The sentence that follows says:

   When a BFD session monitors an explicit routed
   path there is a need to be able to direct egress BFD peer to use
   specific path for the reverse direction of the BFD session.

The question is — why is there that need?
GIM>> Please see my comment above.

I still believe this is a bit of a non sequitur. Why does BFD monitoring an explicit routed path imply a need to direct the egress on a path for the reverse direction? That’s not generally a “need” in all situations.
GIM2>> Please see modified Abstract above. It uses “may be a need”

I think the passive voice hides precision needed.

The document then goes on to say:

2.  Problem Statement

   BFD is best suited to monitor bi-directional co-routed paths.

But: First, why is this the case? the BFD specifications do not say so.
GIM>> If the paths used by forward and return paths are not co-routed that may create ambiguous situation when interpreting failure detection on the node that sends BFD control packets onto the monitored path, e.g. LSP.

First, the same ambiguity exists with bi-directional co-routed paths — because links and nodes are not the only resources that need to be common. FIBs can be programmed well on one direction and wrongly on the reverse.
GIM2>> BFD, as other continuity check protocols, only performs defect detection. Defect localization and characterization usually performed with other tools. But having co-routed path for a test session reduces, not eliminates but reduces, ambiguity of defects of the reverse path.

Can you please point to a definition of a co-routed path for Segment Routing from the segment routing architectural documents?

Or are you defining that here?

Second, again, why “best suited”? If the BFD specs say that BFD can monitor unidirectional paths (including MPLS LSPs and unidirectional links), seems BFD is not necessarily “best suited to…"
GIM2>> BFD certainly can and being used to monitor uni-directional paths. And usually we don’t think of how the reverse path may affect defect detection or, in case of PM OAM, measured performance metric. Having test session on bi-directional co-routed path makes the test result interpretation more certain.

See above.

And: Second, if there is a co-routed bidirectional path, then there is no need to specify the return path! The return path is basically “back on the other way on this co-routed bidirectional path”, so there is no need for what this document specifies.
GIM>> AFAIK, only MPLS-TP defined p2p bi-directional co-routed LSP. True, co-routed bi-directional tunnel may be constructed by using combination of RSVP’s RRO and ERO as well. But other than that, AFAIK, all objects monitored by multi-hop BFD are not guaranteed to be co-routed.

If the path *is* bi-directional co-routed (by whichever method), you would not need this — the was my point, not that some cases are co-routed and others are not.
GIM>> Yes, and the scope of this proposal is not on already bi-directional co-routed paths, e.g. MPLS-TP p2p bi-directional co-routed LSP. RSVP-TE LSP may be explicitly routed but are unidirectional. And so SR tunnel.

Next sentence:

   be co-routed, thus
   fulfilling the implicit BFD requirement

But BFD never has this requirement, implicit or explicit.
GIM>> If the goal of BFD to ensure reliable detection of failures, then co-routed multi-hop path is implied.

I disagree. Even RFC 5883 says:

   The Bidirectional Forwarding Detection (BFD) protocol [BFD] defines a
   method for liveness detection of arbitrary paths between systems.


   BFD can also be useful on arbitrary paths between systems, which may
   span multiple network hops and follow unpredictable paths.


   Furthermore, a pair of systems may have multiple paths between them
   that may overlap.  This document describes methods for using BFD in
   such scenarios.

GIM2>> Will remove “… thus fulfilling the implicit BFD requirement” from the document.

I am not going to further dissect each sentence, but the point is that if there’s something co-routed, there’s no need to explicitly point to the return path. If there is not, then why?
GIM>> If there’s no co-routedness between a monitored path and the return path, then this draft provides mechanism that may be used to remove possible ambiguity in interpretation of failure of the return path.

2. Technical feasibility

The second major problem area is the actual technical feasibility. A main motivation seems to be “3.1.3.  Segment Routing: MPLS Data Plane Case”.

However, looking at an SR path, it can be constructed by Node-SIDs and Adj-SIDs. Please refer to:

First, Adj-SIDs SHOULD (not MUST) be assigned. This means there is the potential of an Adj-SID not assigned to a local Adj. There’s of course also the cases in which Adj-SIDs can be assigned to bundles, to ECMP/UCMP groups, etc.

The implication here is that there is a possibility that there is no way to exactly explicitly construct a co-routed return path. For example, if the forward path is Node A -> Link X -> Node Z, then the return path needs to go to the node Z. Then it is a loose path (i.e., NOT co-routed) to the adjacent node to A through link X, and then that node needs to have an Adj-SID on the same link, which might not.
GIM>> Appreciate your detailed analysis of the Segment Routing use case. We didn’t spell it out in such details but will be glad to add applicability clarification based on your comment.

I do not think it is about Applicability. Given the existence of Adj-SIDs, the question is about technical feasibility. What do you do in the example I detailed above? Seems like there are potential cases in which it is not possible to specify the actual return path desired.

GIM2>> There are many scenarios where it is possible and useful to specify strict explicit path for SR tunnel. To use strict or loose paths – that we leave to the operator to decide. The proposal addresses real scenario, though not all possible ones.

The document does not seem to include this applicability. Still, can you please point to a definition of a co-routed path for Segment Routing from the segment routing architectural documents?

There seems to be a difference between strict explicit routing (RSVP-TE) and this capability.

3. Actual Protocol Mechanics

Section 3.1.1.  BFD Reverse Path TLV, uses “Target FEC sub-TLV” to define the reverse path. This is consistent with the approach in RFC 7110.

In fact, Section 3.1.2 uses the RFC 7110 sub-TLVs for “Static and RSVP-TE sub-TLVs”.

However, Section 3.1.3, which seems to be a key motivation (“3.1.3.  Segment Routing: MPLS Data Plane Case”), uses “Label Entries” to specify the Path!

I believe this is a serious technical issue. Instead of using Label values, it should use Target FEC Stacks (as with the few other cases above). Labels can change. With labels there is no validation possible that what distributed by a given label distribution protocol is what is meant in the data plane.
GIM>> I don’t see need to use Target FEC Stacks as the purpose of the BFD Reverse Path TLV not to verify mapping between the control and the data planes but to provide the remote BFD peer with pre-computed for the reverse path.

It is not about verification of the control and data planes in the return path.

The reason why RFC 7110 uses FECs and not Labels is that the invariant is the FEC, while the label numerical value can change. Seems like using labels is less robust and more brittle.

GIM2>> If label value changes, i.e. label withdrawn, then BFD return path for the BFD session may be re-signaled via LSP Ping with the same BFD discriminator.

In fact, Section 5.2 is trying to assign this for the Target FEC Stack:

    | X (TBD2) | Segment Routing MPLS Tunnel sub-TLV | This document |

But that’s not a Target FEC! It’s a label value!

This should be done by also using the Target FEC Stack.

The Target FEC Stack for SR is defined at, but surprisingly, draft-ietf-mpls-spring-lsp-ping (and the SR TFC thereby defined) are not even references in this document.
GIM>> We haven’t updated the draft just because I-D.kumarkini-mpls-spring-lsp-ping got adopted by the WG. Will certainly update the reference in the next version.

Section 3.3 of this document does include an older version of that draft, before WG adoption, and is somehow trying to Update it. Instead of updating it from here, it should discuss how to updated it on itself.
GIM>> This document enhances LSP Ping for Segment Routing environment and we’ve proposed clarification to use of LSP Ping in Segment Routing when bootstrapping BFD session that, hopefully, will be discussed by MPLS WG in course of this WGLC and used in draft-ietf-mpls-spring-lsp.

As an aside, it’s not clear to me why WGLCing this document (twice) before moving forward with I-D.kumarkini-mpls-spring-lsp-ping.

draft-ietf-mpls-spring-lsp-ping-00 seems to be a dependency to advance before this.

I still do not understand the technical reason to use MPLS labels and not FECs. Further, using labels can suffer from misdirection if Label assignment changes (for a stable given FEC)
GIM2>> Return path may be re-signaled in such case.

The Section that follows is: “3.2.  Segment Routing: IPv6 Data Plane Case”, but in this case, I am mostly confused and baffled on how a set of IPv6 addresses can be an MPLS Target FEC Stack.
GIM>> Agree, IPv6 case is outside the MPLS WG and I’ll remove it for further study.


The issue about using labels (along with the other ones) still remain.

4. IPR

This document has IPR with specific licensing terms. I would like to understand what parts of the document are potentially covered and understand if there’s ways to work around that.

In summary, browsing through the document, I see high-level problem area issues, feasibility issues, technology issues, and others. Happy to be shown incorrect if I missed or confused anything.




— Carlos.


— Carlos.

On Jul 10, 2016, at 1:59 PM, Martin Vigoureux <<>> wrote:


as said by Ross [1], I have been appointed Document Shepherd for draft-ietf-mpls-bfd-directed [2]. As such I am also running the second WG LC.

So, this e-mail starts a WG LC which will end on the 31st of July.

I'd like to remind that an IPR disclosure [3] exists against this document.

So it is time to state whether or not you are in favour of progressing the document. Please also take the time to review the document and post comments on its content.

Please respond to this call.

Thank you



mpls mailing list<>