Re: [mpls] Review of draft-ietf-mpls-residence-time-12

John E Drake <> Thu, 19 January 2017 21:19 UTC

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From: John E Drake <>
To: "Les Ginsberg (ginsberg)" <>, "Acee Lindem (acee)" <>, Alexander Vainshtein <>, Greg Mirsky <>
Thread-Topic: [mpls] Review of draft-ietf-mpls-residence-time-12
Date: Thu, 19 Jan 2017 21:19:17 +0000
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Cc: "Abhay Roy \(akr\)" <>, "" <>, "" <>, "" <>, "" <>, Robert Sparks <>, "" <>
Subject: Re: [mpls] Review of draft-ietf-mpls-residence-time-12
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I understand and I have made the same argument in other contexts and with similar results ("... and your point is?").

However, as I indicated in my previous email, RTM would be used as part of the network infrastructure as a way to provide time synchronization between the nodes in the network, so I would consider it similar to the S-BFDs that Uma and you were discussing.

Yours Irrespectively,


From: Les Ginsberg (ginsberg) []
Sent: Thursday, January 19, 2017 4:09 PM
To: John E Drake <>et>; Acee Lindem (acee) <>om>; Alexander Vainshtein <>om>; Greg Mirsky <>
Cc: Robert Sparks <>om>;;;;;; Abhay Roy (akr) <>
Subject: RE: [mpls] Review of draft-ietf-mpls-residence-time-12

John -

The text you have excerpted below was trying to say two things:

1)If you want to advertise this in the IGPs the OSPF style proposal is much better from an implementation standpoint than the IS-IS GENAPP proposal

2)There is a larger question as to whether we should be using the IGPs for this at all

Statement #1 should not be interpreted to imply that I am advocating using the IGPs. :)

That said, we "ALWAYS" end up choosing using the IGPs to do this sort of thing - not because it is the "RIGHT" thing to do architecturally - but because it is so convenient.

I am just asking for folks to pause and think about this a bit more from an architectural perspective.


From: John E Drake []
Sent: Thursday, January 19, 2017 12:20 PM
To: Les Ginsberg (ginsberg); Acee Lindem (acee); Alexander Vainshtein; Greg Mirsky
Cc: Robert Sparks;<>;<>;<>;<>;<>; Abhay Roy (akr)
Subject: RE: [mpls] Review of draft-ietf-mpls-residence-time-12


Comments inline.

Yours Irrespectively,


From: Les Ginsberg (ginsberg) []
Sent: Thursday, January 19, 2017 12:25 PM
To: John E Drake <<>>; Acee Lindem (acee) <<>>; Alexander Vainshtein <<>>; Greg Mirsky <<>>
Cc: Robert Sparks <<>>;<>;<>;<>;<>;<>; Abhay Roy (akr) <<>>
Subject: RE: [mpls] Review of draft-ietf-mpls-residence-time-12

John -

For me, this raises the age-old question of when it is/is not appropriate to use IGPs for flooding information.

This is clearly not TE information - you just happen to be using this in conjunction with MPLS - but it is a generic capability. I do not see the IGPs as the appropriate mechanism to flood generic interface capabilities. It also, as Acee has pointed out, results in flooding information to all nodes in the domain when only a few care about it.

[JD]  RTM support as defined in the draft would be used to provide extremely accurate time synchronization in an MPLS network so I would suggest that all nodes in such a network would be using it and hence that it does belong in the IGP.  As an aside, advertising it in the IGP facilitates incremental or partial deployment.  Your yesterday's email supports this:

"It would seem more appropriate to treat RTM information either as:

   o an extension to link attribute information already advertised by the IGPs (as has been suggested for OSPF) - which would suggest in IS-IS a sub-TLV of TLV 22(et al)


*        As an interface attribute independent of routing protocols which could be retrieved utilizing network management tools"


From: John E Drake []
Sent: Thursday, January 19, 2017 8:54 AM
To: Acee Lindem (acee); Alexander Vainshtein; Greg Mirsky; Les Ginsberg (ginsberg)
Cc: Robert Sparks;<>;<>;<>;<>;<>; Abhay Roy (akr)
Subject: RE: [mpls] Review of draft-ietf-mpls-residence-time-12


Relying on an omniscient controller is a non-starter in general and in particular because the protocol by which it would learn each node's RTM capabilities and distribute them to the other nodes is undefined.  Further, one of the ways by which an omniscient controller learns a node's capabilities is by snooping the link/state database.

Yours Irrespectively,


From: Acee Lindem (acee) []
Sent: Thursday, January 19, 2017 11:47 AM
To: John E Drake <<>>; Alexander Vainshtein <<>>; Greg Mirsky <<>>; Les Ginsberg (ginsberg) <<>>
Cc: Robert Sparks <<>>;<>;<>;<>;<>;<>; Abhay Roy (akr) <<>>
Subject: Re: [mpls] Review of draft-ietf-mpls-residence-time-12

Hi John,

From: John E Drake <<>>
Date: Thursday, January 19, 2017 at 10:43 AM
To: Acee Lindem <<>>, Alexander Vainshtein <<>>, Greg Mirsky <<>>, "Les Ginsberg (ginsberg)" <<>>
Cc: Robert Sparks <<>>, "<>" <<>>, "<>" <<>>, "<>" <<>>, "<>" <<>>, "<>" <<>>, "Abhay Roy (akr)" <<>>
Subject: RE: [mpls] Review of draft-ietf-mpls-residence-time-12


We discussed all of this with you over a year ago and used your guidance in adding the indication of RTM capability to OSPF.

I'm sorry but I focused mainly on the OSPF protocol aspects then and didn't question the use case. This question came up in the IS-IS WG discussions.


Yours Irrespectively,


From: Acee Lindem (acee) []
Sent: Thursday, January 19, 2017 11:38 AM
To: Alexander Vainshtein <<>>; Greg Mirsky <<>>; Les Ginsberg (ginsberg) <<>>
Cc: Robert Sparks <<>>;<>;<>;<>;<>;<>; Abhay Roy (akr) <<>>
Subject: Re: [mpls] Review of draft-ietf-mpls-residence-time-12

I guess what we were trying to envision the use case and whether it makes sense for all the nodes in the IGP routing domain to have this information. Would the LSP ingress LSR only need to if the egress LSR supports RTM and it is best effort recording for transit LSRs in the path?

Additionally, if it is needed in the IGPs, should there also be a BGP-LS Link Attribute TLV proposed?


From: Alexander Vainshtein <<>>
Date: Thursday, January 19, 2017 at 10:15 AM
To: Greg Mirsky <<>>, "Les Ginsberg (ginsberg)" <<>>
Cc: Acee Lindem <<>>, Robert Sparks <<>>, "<>" <<>>, "<>" <<>>, "<>" <<>>, "<>" <<>>, "<>" <<>>, "Abhay Roy (akr)" <<>>
Subject: RE: [mpls] Review of draft-ietf-mpls-residence-time-12

Hi all,
I concur with Greg: from my POV an interoperable solution should not depend on an omniscient NMS client distributing information about capabilities of each node to each other node.


Office: +972-39266302
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From: Greg Mirsky []
Sent: Thursday, January 19, 2017 6:01 PM
To: Les Ginsberg (ginsberg) <<>>
Cc: Acee Lindem (acee) <<>>; Robert Sparks <<>>;<>;<>;<>;<>;<>; Abhay Roy (akr) <<>>
Subject: Re: [mpls] Review of draft-ietf-mpls-residence-time-12

Hi Les,
I believe that IGP extensions to advertise RTM capability are required.


On Thu, Jan 19, 2017 at 7:57 AM, Les Ginsberg (ginsberg) <<>> wrote:
Greg -

I am having trouble understanding your response.
The question we are raising is whether we should extend the IGPs to support advertising RTM capability - an alternative being to retrieve the capability via network management.

Saying that the IGP functionality is optional and/or wouldn't always be advertised doesn't really answer the question of whether we should or should not define the IGP extensions.

Could you respond more directly to this point?


From: Greg Mirsky [<>]
Sent: Thursday, January 19, 2017 7:44 AM
To: Acee Lindem (acee)
Cc: Robert Sparks;<>;<>;<>;<>; Les Ginsberg (ginsberg);<>; Abhay Roy (akr)

Subject: Re: [mpls] Review of draft-ietf-mpls-residence-time-12

Hi Acee,
the draft defines optional functionality. If an operator has no use neither for PTP's Transparent Clock, nor RTM itself as performance metric, then RTM sub-TLV would not be included and thus it would not be flooded. Of course, it be right to reflect RTM capability through YANG data model, thus allowing SDN scenario you've described.


On Wed, Jan 18, 2017 at 2:51 PM, Acee Lindem (acee) <<>> wrote:
Hi Greg,

Although it is a bit late, we've had some discussions amongst the IS-IS and OSPF chairs and are wondering whether the interface capability belongs in the IGPs. This will be flooded throughout the entire routing domain - is it really needed on every node or will it the RTM testing be initiated from an omniscient NMS client that would know the capabilities of each node or easily query them using YANG?


From: mpls <<>> on behalf of Greg Mirsky <<>>
Date: Wednesday, January 18, 2017 at 1:25 PM
To: Robert Sparks <<>>
Cc: "<>" <<>>, "<>" <<>>, "<>" <<>>, "<>" <<>>
Subject: Re: [mpls] Review of draft-ietf-mpls-residence-time-12

Hi Robert,
thank you for the most expedient review and comments. I'll make changes in Section 2 per your suggestion.


On Wed, Jan 18, 2017 at 10:34 AM, Robert Sparks <<>> wrote:

The changes all look good.

I still think you should say something in the document about what "the time of packet arrival" and "transmission" means, and call out the point you made about being careful to not introduce apparent jitter by not making those measurements consistently. (The definitions you point to in your earlier mail from G.8013 don't really help - they just say "time of packet arrival". Again, the first and last bit are likely to be several nanoseconds apart so I think it matters. Perhaps you're saying it doesn't matter as long as each node is consistent (there will be error in the residence time measurement, but it will be constant at each node, so the sum of errors will be constant, and the clocks will be ok?)

Please look at the new first paragraph of section 2 - there's a mix of "as case" and "in case" that should be made consistent. I suspect it would be easiest to simply say "referred to as using a one-step clock" and "referred to as using a two-step clock" or similar.


On 1/18/17 12:03 PM, Greg Mirsky wrote:
Hi Robert,
Sasha Vainshtein came with elegant idea to address disconnection between discussion of one-step and two-step modes that you've pointed out. We've moved Section 7 as sub-section into Section 2 now. Attached are updated diff and the proposed new version -13.


On Wed, Jan 18, 2017 at 8:13 AM, Greg Mirsky <<>> wrote:
Hi Robert,
once again, thank you for your thorough review and the most detailed comments. I've prepared updated version and would greatly appreciate if you review the changes and let us know whether your comments been addressed. Attached are diff and the new version.


On Wed, Jan 11, 2017 at 7:48 AM, Robert Sparks <<>> wrote:
Reviewer: Robert Sparks
Review result: Ready with Nits

I am the assigned Gen-ART reviewer for this draft. The General Area
Review Team (Gen-ART) reviews all IETF documents being processed
by the IESG for the IETF Chair.  Please treat these comments just
like any other last call comments.

For more information, please see the FAQ at

Document: draft-ietf-mpls-residence-time-12
Reviewer: Robert Sparks
Review Date: 2017-01-10
IETF LC End Date: 2017-01-17
IESG Telechat date: 2017-02-02

Summary: Ready (with nits) for publication as a Proposed Standard

I have two primary comments. I expect both are rooted in the authors
and working group knowing what the document means instead of seeing
it says or doesn't say:

1) The document is loose with its use of 'packet', and where TTLs
appear when
they are discussed. It might be helpful to rephrase the text that
of RTM packets in terms of RTM messages that are encoded as G-ACh
messages and
not refer to packets unless you mean the whole encapsulated packet
with MPLS
header, ACH, and G-ACh message.

2) Since this new mechanic speaks in terms of fractional nanoseconds,
discussion of what trigger-point you intend people to use for taking
precise time of a packet's arrival or departure seems warranted. (The
first and
last bit of the whole encapsulated packet above are going to appear at
physical layer many nanoseconds apart at OC192 speeds if I've done the
right). It may be obvious to the folks discussing this, but it's not
from the document.  If it's _not_ obvious and variation in technique
expected, then some discussion about issues that might arise from
implementation choices would be welcome.

The rest of these are editorial nits:

It would help to pull an overview description of the difference
one-step and two-step much earlier in the document. I suggest in the
in section 2. Otherwise, the reader really has to jump forward and
read section
7 before section 3's 5th bullet makes any sense.

In section 3, "IANA will be asked" should be made active. Say "This
asks IANA to" and point to the IANA consideration section. Apply
treatment to the other places where you talk about future IANA

There are several places where there are missing words (typically
articles or
prepositions). You're less likely to end up with misinterpretations
during the
RFC Editor phase if you provide them before the document gets that far
in the
process. The spots I found most disruptive were these (this is not
intended to
be exhaustive):

  Section 3: "set 1 according" -> "set to 1 according"
  Section 3: "the Table 19 [IEEE..." -> "Table 19 of [IEEE..."
  Section 4.2: "Detailed discussion of ... modes in Section 7."
                        -> "Detailed discussion of ... modes appears
in Section 7."
  Section 10: "most of" -> "most of all"

In Setion 3.1 at "identity of the source port", please point into the
that defines this identity and its representation. I suspect this is a
into a specific section in IEEE.1588.2008].