This is a well written document with a technical point that needs addressing and a couple of small nits, other than that it is ready to go.

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Early deployments may support a so called
   "Entropy label" for this purpose.  State of the art deployments base
   their choice of an ECMP member based on the IP addresses (see
   Section 2.4 of [RFC7325]).  

The entropy label is a relatively modern concept and I am not sure how widely it is deployed. Older routers used either a hash on the labels as far down the stack as they could reach (the goal was to include the BoS label this was a VPN or a PW), or (more commonly) reached over the label stack (sometimes incorrectly) and hash on the five tuple of the payload.

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This procedure requires to compute quartile values "on the fly" using
the algorithm presented in [P2].

Minor English issue - missing text after requires
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For reasons pointed out by one of the other reviewers, it is a pity that Class C is used, but it seems to be well embedded in the technology and would be difficult to change.
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Nits says that there is a requirements language problem. I think that may be that it is simply in the wrong place. It would be good if it were fixed to prevent other reviewers also needing to deal with this point