Re: [Lsr] IGP TE Metric Extensions

"Les Ginsberg (ginsberg)" <> Wed, 06 June 2018 05:42 UTC

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From: "Les Ginsberg (ginsberg)" <>
To: Muthu Arul Mozhi Perumal <>, Robert Raszuk <>
CC: "" <>, Jeff Tantsura <>, "Stefano Previdi (IETF)" <>
Thread-Topic: [Lsr] IGP TE Metric Extensions
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Date: Wed, 6 Jun 2018 05:42:51 +0000
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Subject: Re: [Lsr] IGP TE Metric Extensions
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Muthu –

I agree with the comments from all of the folks who have responded to you thus far.
The RFC is specifying what the externally visible behavior needs to be in order for the feature to be safely and usefully deployed – it is not specifying HOW to implement that behavior.

But, let’s assume for the moment that you are “right” and that the draft wording is suggesting that configuration knobs for the thresholds/filters should be owned by the IGP.
If, despite this “suggestion”, you were to decide to implement the knobs elsewhere (e.g., under the interface) – would it affect interoperability? Would it be detectable from the vantage point of another router?

I don’t agree with your interpretation –and I don’t feel that any change in the text is needed.
But I do defend your right to implement the knobs wherever you like.

However, before making your decision you might want to consider - which is relevant from a manageability perspective. Your choice of where to put the knobs might indeed matter (though not to the IGP externally visible behavior).


From: Lsr <> On Behalf Of Muthu Arul Mozhi Perumal
Sent: Tuesday, June 05, 2018 6:26 PM
To: Robert Raszuk <>
Cc:; Jeff Tantsura <>om>; Stefano Previdi (IETF) <>
Subject: Re: [Lsr] IGP TE Metric Extensions


On Tue, Jun 5, 2018 at 9:28 PM, Robert Raszuk <<>> wrote:

​How is the measurement interval and filter coefficients described in the draft related to dissemination?​

​It is directly related. If you see the title of the section is: "Announcement Thresholds and Filters"​

So measurement interval does not intend to describe how often you actually measure ... it describes a time window where you report the value (which could consist of many measurements actually taken).

​Are you saying measurement interval is a misnomer? The draft clearly distinguishes measurement interval from announcement interval:

​   Additionally, the default measurement interval for all sub-TLVs
   SHOULD be 30 seconds.

   Announcements MUST also be able to be throttled using configurable
   inter-update throttle timers.  The minimum announcement periodicity
   is 1 announcement per second.  The default value SHOULD be set to 120

Yet, it claims measurements are outside its scope..

We intentionally left out this part that does not belong to the igp protocol machinery.

​Which of the functionalities described in sections 5, 6, 7 of the draft belong to the IGP protocol machinery?

​What draft are you talking about ? I was under impression that we are discussing RFCs here.

​Well, both -:) I am referring to draft-ginsberg-lsr-isis-rfc7810bis and I believe there is a chance to improve some text in RFC7810..


​All functionality from sections 5-7 aim to provide machinery to control stability of protocol operation. It is one how you measure and this is not part of the RFCs. and completely different what and how you advertised derived values from those gathered by your measurements. Now keeping in mind that you do not advertise when you measure but only when you are allowed by protocol rules it should be easy to see the point which Stefano made above.