[Roll] John Scudder's Discuss on draft-ietf-roll-aodv-rpl-10: (with DISCUSS and COMMENT)
John Scudder via Datatracker <noreply@ietf.org> Mon, 19 April 2021 20:31 UTC
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Date: Mon, 19 Apr 2021 13:31:58 -0700
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Subject: [Roll] John Scudder's Discuss on draft-ietf-roll-aodv-rpl-10: (with DISCUSS and COMMENT)
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John Scudder has entered the following ballot position for draft-ietf-roll-aodv-rpl-10: Discuss When responding, please keep the subject line intact and reply to all email addresses included in the To and CC lines. (Feel free to cut this introductory paragraph, however.) Please refer to https://www.ietf.org/iesg/statement/discuss-criteria.html for more information about DISCUSS and COMMENT positions. The document, along with other ballot positions, can be found here: https://datatracker.ietf.org/doc/draft-ietf-roll-aodv-rpl/ ---------------------------------------------------------------------- DISCUSS: ---------------------------------------------------------------------- A lot of effort has clearly gone into this work, thank you. I do have one topic I want to DISCUSS, as it seriously impacted the readability of the document from my point of view. I don’t anticipate that it will be very difficult to resolve this DISCUSS as it relates to clarity and not to anything fundamental. My chief difficulty with the document is placing it in context. No hints are given to the reader as to what the expected network environment is. I think it would be almost sufficient to say, for example “the network environment is assumed to be the same as described in RFC 6550, Section 1” for example, but without that hint and without a strong background in ROLL, I found myself struggling. Figures 4 and 5 in particular lead me to believe the expected environment looks similar to a classic ISP network — a collection of nodes connected by point-to-point links. If this isn’t correct (and I bet it’s not) that may have led me into incorrect assumptions, which may be reflected in my other comments below. Further, it’s not stated anywhere whether AODV-RPL is intended to stand alone as its own routing protocol, or to be viewed as an extension of RPL. In the former case, it seems the document is lacking details that are present in RFC 6550. I’m assuming the latter is the case, but a clear statement to that effect seems indicated. ---------------------------------------------------------------------- COMMENT: ---------------------------------------------------------------------- 1. Section 1: Reply. AODV-RPL currently omits some features compared to AODV -- in particular, flagging Route Errors, blacklisting unidirectional links, multihoming, and handling unnumbered interfaces. Your use of language is entirely up to you, but I feel obliged to point out that there’s been a lot of discussion in the IETF community recently about use of language that raises sensitive points, and about the term “blacklisting” in particular. I understand that this is the only place in the document the term appears, and since it refers to AODV you can’t just use another term, but placing it in quotation marks might make it clear that it’s referring verbatim to the language of RFC 3561. 2. Section 1: support for storing and non-storing modes. AODV adds basic messages RREQ and RREP as part of RPL DIO (DODAG Information Object) control Did you mean “AODV-RPL adds”? 3. Section 2: Symmetric route The upstream and downstream routes traverse the same routers. Same routers? Or same links? (Or both, if multi-access links are part of the mix, as I imagine they may be?) 4. Section 4.1: OrigNode sets its IPv6 address in the DODAGID field of the RREQ-DIO message. A RREQ-DIO message MUST carry exactly one RREQ option, Should that say “one of its IPv6 addresses"? Is it even necessary to restate this? RFC 6550 §6.3.1 already has a clearer requirement: DODAGID: 128-bit IPv6 address set by a DODAG root that uniquely identifies a DODAG. The DODAGID MUST be a routable IPv6 address belonging to the DODAG root. 5. Section S4.1: TargNode can join the RREQ instance at a Rank whose integer portion is equal to the MaxRank. Not less than or equal, right? Strict equality to MaxRank is required? 6. Section 4.2: TargNode sets its IPv6 address in the DODAGID field of the RREP-DIO message. A RREP-DIO message MUST carry exactly one RREP option, Same as #4. 7. Section 4.2: Address Vector Only present when the H bit is set to 0. For an asymmetric route, the Address Vector represents the IPv6 addresses of the route that the RREP-DIO has passed. The first time I read through this, I didn’t understand it at all. On re-reading, I think you’re using the word “route” in two different ways in the same sentence, the first time to mean “route” in the sense of an object in the protocol, the second time in the more casual sense of “a path through the network”. If that’s right, I suggest rewriting the second instance, as in “… represents the IPv6 addresses of the path through the network the RREP-DIO has traversed.” Also, as in point #4, is it right to say *the* IPv6 addresses? Couldn’t any given node have various IPv6 addresses? So maybe just lose the definite article, as in “… represents IPv6 addresses of the path…”? 8. Section 4.3: r A one-bit reserved field. This field MUST be initialized to zero by the sender and MUST be ignored by the receiver. The figure doesn’t show an “r” field. I assume the field labeled “X” should be relabeled as “r”? 9. Section 5: Figure 4. If an intermediate router sends out RREQ-DIO with the S bit set to 1, then all the one-hop links on the route from the OrigNode O to this router meet the requirements of route discovery, On first reading I didn’t understand this. Having read the whole document, I now get it (I think!). Possibly changing “meet” to “have met” would have been enough to get me past my initial befuddlement. 10. Section 5: The criteria used to determine whether or not each link is symmetric is beyond the scope of the document. For instance, intermediate Should be “criterion … is beyond", or "criteria … are beyond", depending on whether you want singular or plural. 11. Section 5: routers can use local information (e.g., bit rate, bandwidth, number of cells used in 6tisch) I wouldn’t have minded a reference for 6tisch. 12. Section 5: Upon receiving a RREQ-DIO with the S bit set to 1, a node determines whether this one-hop link can be used symmetrically, i.e., both the two directions meet the requirements of data transmission. If the RREQ-DIO arrives over an interface that is not known to be symmetric, or is known to be asymmetric, the S bit is set to 0. If the S bit arrives already set to be '0', it is set to be '0' on retransmission The term “retransmission” seems misused here. I guess you mean something like “when the RREQ-DIO is propagated”. 13. Section 5: Appendix A describes an example method using the upstream Expected Number of Transmissions" (ETX) and downstream Received Signal Strength Indicator (RSSI) to estimate whether the link is symmetric in terms of link quality is given in using an averaging technique. This sentence needs a rewrite to make it grammatical. It works up until "is given in using an averaging technique”. 14. Section 6.2.1: If the S bit in the received RREQ-DIO is set to 1, the router MUST determine whether each direction of the link (by which the RREQ- DIO is received) satisfies the Objective Function. In case that the downward (i.e. towards the TargNode) direction of the link does not satisfy the Objective Function, the link can't be used symmetrically, thus the S bit of the RREQ-DIO to be sent out MUST be set as 0. If the S bit in the received RREQ-DIO is set to 0, the router MUST determine into the upward direction (towards the OrigNode) of the link. The last sentence doesn’t make sense. 15. Section 6.2.1: If the router is an intermediate router, then it transmits a RREQ- DIO via link-local multicast; On what interface? Routers generally can have multiple interfaces. Again, this is a place a clear description of the network environment might have helped. 16. Section 6.2.2: If the OrigNode tries to reach multiple TargNodes in a single RREQ- Instance, one of the TargNodes can be an intermediate router to the others, therefore it MUST continue sending RREQ-DIO to reach other targets. In this case, before rebroadcasting the RREQ-DIO The use of the term “broadcast” here confuses me. Is this “broadcast” in the RF sense? Again, this is a place a clear description of the network environment might have helped. 17. Section 6.2.2: send out any RREQ-DIO. For the purposes of determining the intersection with previous incoming RREQ-DIOs, the intermediate router maintains a record of the targets that have been requested associated with the RREQ-Instance. Any RREQ-DIO message with different ART Options coming from a router with higher Rank is ignored. It’s not clear to me if the last sentence goes with the previous and if so, how. Does it even relate to multiple targets? Also, different from what? If it has the same ART Options (same as what?) is it *not* ignored? 18. Section 6.3.1: implementation-specific and out of scope. If the implementation selects the symmetric route, and the L bit is not 0, the TargNode MAY delay transmitting the RREP-DIO for duration RREP_WAIT_TIME to await a symmetric route with a lower Rank. The value of RREP_WAIT_TIME is set by default to 1/4 of the time duration determined by the L bit. It’s not an L bit though, it’s an L field. 19. Section 6.3.2: multicast until the OrigNode is reached or MaxRank is exceeded. The TargNode MAY delay transmitting the RREP-DIO for duration RREP_WAIT_TIME to await a route with a lower Rank. The value of RREP_WAIT_TIME is set by default to 1/4 of the time duration determined by the L bit. Again, it’s an L field. Also, what if L is zero? Is RREP_WAIT_TIME set to infinity, as the text implies? Please do a global search for “L bit”, as there are additional instances I haven’t called out. 20. Section 6.4: Step 4: If the receiver is the OrigNode, it can start transmitting the application data to TargNode along the path as provided in RREP- Instance, and processing for the RREP-DIO is complete. Otherwise, in case of an asymmetric route, the intermediate router MUST include the address of the interface receiving the RREP-DIO into the address vector, and then transmit the RREP-DIO via link-local multicast. In case of a symmetric route, the RREP-DIO message is As with #15: on what interface(s)? 21. Section 10: fake AODV-RPL route discoveries. In this type of scenario, RPL's preinstalled mode of operation, where the key to use for a P2P-RPL route discovery is preinstalled, SHOULD be used. What type of scenario is that? 22. Appendix A: s/pakcet/packet/ 23. General remark: Although “acknowledgements” isn’t a required section I was a little surprised not to encounter it, as it’s usually present. Your call of course.
- [Roll] John Scudder's Discuss on draft-ietf-roll-… John Scudder via Datatracker
- Re: [Roll] John Scudder's Discuss on draft-ietf-r… Alvaro Retana
- Re: [Roll] John Scudder's Discuss on draft-ietf-r… John Scudder
- Re: [Roll] John Scudder's Discuss on draft-ietf-r… Alvaro Retana
- Re: [Roll] John Scudder's Discuss on draft-ietf-r… John Scudder
- Re: [Roll] John Scudder's Discuss on draft-ietf-r… Charlie Perkins
- Re: [Roll] John Scudder's Discuss on draft-ietf-r… John Scudder
- Re: [Roll] John Scudder's Discuss on draft-ietf-r… Charlie Perkins
- Re: [Roll] John Scudder's Discuss on draft-ietf-r… Ines Robles
- Re: [Roll] John Scudder's Discuss on draft-ietf-r… Ines Robles
- Re: [Roll] John Scudder's Discuss on draft-ietf-r… John Scudder