Hi,

I have reviewed this document as part of the Operational directorate's ongoing
effort to review all IETF documents being processed by the IESG.  These
comments were written with the intent of improving the operational aspects of
the IETF drafts per guidelines in RFC5706.

Comments that are not addressed in last call may be included
in AD reviews during the IESG review.  Document editors and WG chairs should
treat these comments just like any other last call comments.

Overall Summary:

This draft is a standard track proposing a new bit in the RPL DODAG Configuration Option (defined in RFC6550) and update the compression behavior defined in RFC8130.

Overall this is a very well written document. Some ambiguities that need attention are listed below. 

More details below:

--> Section 3 assigns a bit from the Configuration Options. This flag field is instructed by RFC6550 to set to zero and should be ignored by the receiver. So I think this draft should also update RFC6550 (in addition to RFC 8138).

--> I understand that the T flag is mentioned as bit position 2 in section 6. AFAIK, bit position may start from 0 and can be LSB/MSB. To avoid confusing (and any interop issues), I think the flag can be clarified in Fig 1 (or by just defining another figure with the updated flag field).

A node SHOULD source packets in the compressed form using [RFC8138]
   if and only if the "T" flag is set.  This behaviour can be overridden
   by e.g., configuration or network management.
      
--> It appears that the above overriding exception can be interpreted as either of the below:

Opt1 - A config knob can be used to let a node source packets in [RFC8138] compressed form  even if T flag is not set.
Opt2 - A config knob can be used to let a node source packets without compression even if T flag is set.

Further section 5.2 mentions the below:

"To ensure that a packet is forwarded across the RPL DODAG in the form
   in which it was generated, it is required that all the RPL nodes
   support [RFC8138] at the time of the switch."
   
So I assume that the config exception is applicable only for Opt2?. I think it is good to clarify the same to avoid any misinterpretation.

Thanks,
Nagendra