As part of the IoT-Directorate review process, I went through draft-ietf-roll-useofrplinfo-40. In general, I believe the document is ready to proceed once a couple of issues that I outline below are resolved. 

I have concerns whether the use of the normative language is appropriate in the use cases section. I believe all such cases are covered either in the sections updating RFC 6553, RFC 6550 and RFC 8138 or in these respective RFCs. Please consider using lowercase keywords in Section 6.

As a minor note, there also appears to be an inconsistent use of the IP6-IP6 acronym. Please use a single acronym throughout the doc, currently a mix of IPv6-in-IPv6 and IP6-IP6 is present.

My detailed comments are given below.

Section 1:

> Since some of the uses cases here described, use IPv6-in-IPv6 encapsulation.  It MUST take in consideration, when encapsulation is applied, the RFC6040 [RFC6040], which defines how the explicit congestion notification (ECN) field of the IP header should be constructed on entry to and exit from any IPV6-in-IPV6 tunnel.
- Please clarify the sentence. Consider whether it is appropriate to have a normative MUST here.

Section 4.2:
> The non-storing mode case does not require the type change from 0x63 to 0x23, as the root can always create the right packet.  The type change does not adversely affect the non-storing case.
- It is not clear what RPI option type should non-storing networks use. A pointer to the discussion in Section 4.3 would be useful.

Section 4.4:

> A node that is decompressing this header MUST decompress using the RPI Option Type that is currently active: that is, a choice between 0x23 (new) and 0x63 (old). The node will know which to use based upon the presence of the flag in the DODAG Configuration option defined in Section 4.3. E.g.  If the network is in 0x23 mode (by DIO option), then it should be decompressed to 0x23.
- If my understanding is correct, this means that in order to decompress data plane packets, a node first needs to remember the option type mode the network is operating in, advertised in DIOs. Consequently, decompression is not possible before at least one DIO is received. 

Section 6:

> The RPI MUST be present in every single RPL data packet.
- How is the normative text here appropriate at this point? Is this not redundant with RFC6553?

>  This document assumes that the LLN is using the no-drop RPI Option Type (0x23).
- This statement appears twice in the document and is as such redundant. please remove one appearance.

Section 8:

> The root always have to encapuslate on the way down
- It is not clear how come does root need to always encapsulate on the way down. In the basic case of root to RAL communication, IPv6-in-IPv6 is marked as “No”. Please clarify.

Section 8.1.3:

> When the RPI is added, the RUL, which does not understand the RPI, will ignore it (per [RFC8200]); thus, encapsulation is not necessary.
- Figure 22 states that for root to RUL communication IPv6-in-IPv6 encapsulation is mandatory which is not consistent with this text.

Section 8.2.1:

- A sentence stating how does RAL recognize that the packet is destined for the Internet would be useful.

Section 8.2.3:

> As RPL headers are added in the RUL packet, the first 6LR (6LR_1) will add an RPI inside a new IPv6-in-IPv6 header.
- this statement makes it sound as if RUL originates a packet with RPL headers. Please rephrase.

Nits:
> The ROLL WG analysized how [RFC2460] rules apply to storing and non-storing use of RPL.
- s/analysized/analyzed 

> that transports that abstract information in an IPv6 Hob-by-Hop Header.
- s/hob/hop

> consumed Routing Header and to ignore a HbH header as prescribed by
- define HbH, assuming Hop-by-Hop

> The root does not removes the RPI1
- s/removes/remove

> The 6LR_ia (ia=1) (Node E) 
- s/6LR_ia (ia=1)/6LR_1

> The root always have to encapuslate on the way down
- s/have to encapuslate/has to encapsulate

>  If the originating node does not not
- s/does not not/does not

> and add it's own
- s/it’s/its

> The migration procedure it is triggered when the DIO is sent with the flag indicating the new RPI Option Type.
- s/it is/is

> Namely, it remains at 0x63 until it is sure that the network is capable of 0x23, then it abruptly change to 0x23.
- s/change/changes