Re: [mpls] MPLS-RT experts review for draft-gandhi-mpls-rfc6374-sr

Greg Mirsky <> Sat, 13 June 2020 02:07 UTC

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From: Greg Mirsky <>
Date: Fri, 12 Jun 2020 19:06:20 -0700
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To: Huaimo Chen <>
Cc: Tarek Saad <>, "" <>, "" <>, "" <>
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Subject: Re: [mpls] MPLS-RT experts review for draft-gandhi-mpls-rfc6374-sr
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Hi Huaimo,
thank you for your comments. Though I am not a co-author of the draft, I am
very interested in the topic. I have a question related to your comments
and conclusions below:

   - you've noted "It seems that the Performance Measurement for a SR P2MP
   Path (or policy) is limited to one way and out-of-band. Should the document
   add some texts talking about these limitations?" If that truly is the case,
   i.e., the proposed OAM mechanism can only work as out-of-band, what is the
   value of the measurement results using the synthetic method of measurement?
   If, as you have noted, a test packet does not follow the monitored data
   flow, how trustworthy and useful the loss and delay measurement are
   achieved? I think that I cannot agree with your conclusion that the prosed
   PM OAM mechanism can only work as out-of-band tool, i.e., support direct
   measurement statistics by collecting counters. The fact that a test packet,
   as described in the draft, uses the precisely same policies as a data
   packet, in my view, ensures that it is in-band and shares the fate with the
   data flow, which is essential to obtaining useful performance measurements.

I much appreciate your consideration of my question.


On Mon, Jun 8, 2020 at 8:52 PM Huaimo Chen <>

> Hi All,
>     I have reviewed the document and have the following comments.
>     1.  The document is useful and technically sound. It can be considered
> for WG adoption.
>     2.  The document seems talking about the Loss Measurement Message
> and Delay Measurement Message. Should it have some texts for Combined
> Loss/Delay Measurement Message?
>     3.  There are a couple of IETF drafts about SR P2MP Path.. The
> document just mentions one of them and the Performance Measurement for a SR
> P2MP Path (or policy) is based on this one draft. Should the Performance
> Measurement for a SR P2MP Path (or policy) be general enough for all?
>     4.  It seems that the Performance Measurement for a SR P2MP Path (or
> policy) is limited to one way and out-of-band. Should the document add some
> texts talking about these limitations?
>     5.  The registry for the newly defined Return Path TLV Type and Block
> Number TLV Type is missing in the document. Is it the "MPLS Loss/Delay
> Measurement TLV Object" registry?
>     6.  It seems that a new registry should be defined for the Sub-TLV
> types under the Return Path TLV in the document.
>     7.  In section 5.1. and section 6.1., Should "For both SR Links and
> end-to-end measurement for SR-MPLS Policies" be changed to something like
> "For both SR Links and end-to-end SR-MPLS Policies measurements"?
>     8.  In section 6.2., should something like a user case be added into
> the sentence "The Block Number TLV is Mandatory when used.."?
> Best Regards,
> Huaimo
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