Reviewer: Mališa Vučinić
Review result: Ready with Issues
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.
<Ines> In section 3 times the normative vocabulary is used not specially oriented to the use cases but to the general behavior. :
-”The DODAG root MUST force it to zero when passing the packet out to the Internet. The Internet will therefore not see any SenderRank information”
-”an intermediate router that needs to add an extension header (e.g. RH3 or RPL Option) MUST still encapsulate the packet in an (additional) outer IP header”
-“The RPI MUST be present in every single RPL data packet.”: in order to avoid e.g loops
In section 7 where the use cases are explained, we have not used normative language, since they are basically examples.
What do you think?
</Ines>
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.
<Ines>
We specify the use of IP6-IP6 in section 2: “Note: Due to lack of space in some figures (tables) we refer to IPv6-in-IPv6 as IP6-IP6.”
</Ines>
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.
<Ines> New text:
Most of the use cases described therein require the use of IPv6-in-IPv6 packet encapsulation.
When encapsulating and decapsulating packets, RFC 6040 [RFC6040] MUST be applied to map the setting of the explicit congestion notification (ECN) field between inner and outer headers.
The normative is used in order to highlight support of ECN for any tunnelling solutions.
What do you think?
</Ines>
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.
<Ines>
In order to be able to decompress, the node should support RFC8138.
The DODAG configuration Option indicates the setting 0x63 or 0x23.
Note that nodes are not part of the RPL instance indicated in the RPI and should not generate or forward packets for that instance before they receive the first DIO.
In the case of reboot, the node (6LN or 6LR) does not remember the RPI Option Type (i.e., whether or not the flag is set), so the node will not trigger DIO messages until a DIO message is received indicating the RPI value to be used. The node will use the value 0x23 if the network supports this feature.
</Ines>
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?
<Ines> the use of the MUST is to enforce the explanation of the use case when the RPI is present . It tends to add clarification to the reader
As Pascal pointed - RFC 6553 states: “ Datagrams sent between RPL routers MUST include a RPL Option or RPL Source Route Header ([RFC6554]) and MAY include both.“ RFC 8138 requires it at all times for compression. Now we MUST the RPI in all cases, it is simpler.
</Ines>
> 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.
<Ines> Added: “Having the RAL information about the RPL domain, it may encapsulate to the root when the destination is not in the RPL domain of the RAL.”
</Ines>
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.
<Ines> As the RUL parent adds RPL headers in the RUL packet, the first 6LR (6LR_1) will add an RPI inside a new IPv6-in-IPv6 header.
What do you think?
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
<Ines> done </Ines>
> 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
Changes are displayed in https://github.com/roll-wg/useofrplinfo/blob/master/draft-ietf-roll-useofrplinfo-41.txt
Thank you very much again for your useful comments,
Ines.
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