Re: [6lo] Benjamin Kaduk's Discuss on draft-ietf-6lo-blemesh-09: (with DISCUSS and COMMENT)
Benjamin Kaduk <kaduk@mit.edu> Wed, 09 June 2021 20:08 UTC
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Date: Wed, 09 Jun 2021 13:07:55 -0700
From: Benjamin Kaduk <kaduk@mit.edu>
To: Carles Gomez Montenegro <carlesgo@entel.upc.edu>
Cc: The IESG <iesg@ietf.org>, rahul.ietf@gmail.com, 6lo-chairs@ietf.org, draft-ietf-6lo-blemesh@ietf.org, 6lo@ietf.org
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Subject: Re: [6lo] Benjamin Kaduk's Discuss on draft-ietf-6lo-blemesh-09: (with DISCUSS and COMMENT)
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Hi Carles, My apologies -- I seem to have missed this when it first arrived. Thanks for the updates in the -10 and the discussion below -- it all looks good and I've cleared my discuss! Unfortunately, that still leaves it in a state where it "needs 2 more YES or NO OBJECTION positions to pass", so Erik will need to wrangle a couple more ADs to take a look. Thanks again, Ben On Thu, Apr 22, 2021 at 12:39:37PM +0200, Carles Gomez Montenegro wrote: > Hi Benjamin, > > Thank you very much for your feedback, and apologies for the late response. > > We just published an updated version of the draft (revision -10). > > Please find below our inline responses to your comments: > > > > Benjamin Kaduk has entered the following ballot position for > > draft-ietf-6lo-blemesh-09: 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 IESG DISCUSS and COMMENT positions. > > > > > > The document, along with other ballot positions, can be found here: > > https://datatracker.ietf.org/doc/draft-ietf-6lo-blemesh/ > > > > > > > > ---------------------------------------------------------------------- > > DISCUSS: > > ---------------------------------------------------------------------- > > > > I may well just be confused about this, but let's discuss and find out. > > Section 3.3.2 says "[a]s per RFC 8505, a 6LN MUST NOT register its > > link-local address." Which part of RFC 8505 says this? Section 5.6 > > thereof seems to enumerate some cases where link-local addresses MUST > > (not MUST NOT) be registered, and there's not much other discussion of > > link-local addresses that I saw. > > Thanks for noticing this. The sentence did not explicitly indicate that we > referred to registration with the 6LBR. > > In -10 we have replaced the former sentence by the next new paragraph: > > NEW: > As per RFC 8505, a 6LN link-local address does not need to be unique > in the multilink subnet. A link-local address only needs to be > unique from the perspective of the two nodes that use it to > communicate (e.g., the 6LN and the 6LR in an NS/NA exchange). > Therefore, the exchange of EDAR and EDAC messages between the 6LR and > a 6LBR, which ensures that an address is unique across the domain > covered by the 6LBR, does not need to take place for link-local > addresses. > > > ---------------------------------------------------------------------- > > COMMENT: > > ---------------------------------------------------------------------- > > > > I support Martin (D)'s Discuss (though I think maybe the use-case that > > is in question is the non-homogeneous-MTU case). At a minimum the > > security considerations should be discussing this scenario as a risk, > > but ideally it could be avoided altogether. > > "As per the present specification, the MTU size for IPv6 mesh over BLE > links is 1280 octets." > > (Initially we thought that it might be a good idea to keep the flexibility > offered by the IPSP in this regard, but we finally realized that it was > not such a good idea.) > > > (I also agree with Martin (V)'s comment.) > > We have updated the draft accordingly, thanks to both. > > (Note: we did not receive an email message from Martin Vigoureux, but we > were able to see his feedback on Datatracker.) > > > Section 3.1 > > > > Similarly to RFC 7668, fragmentation functionality from 6LoWPAN > > standards is not used for IPv6 mesh over Bluetooth LE links. > > Bluetooth LE's fragmentation support provided by L2CAP is used when > > necessary. > > > > I don't really understand why it's necessary to say "when necessary". > > If IPv6 requires an MTU of 1280 octets but the BLE link is doing 247 or > > less, doesn't the L2CAP fragmentation always need to be enabled for the > > IPv6 mesh? > > Yes. To avoid confusion, we have removed "when necessary". > > > Section 3.2 > > > > Is it worth reiterating that with the multi-link subnet model, the > > routers have to take on responsibility for tracking multicast state and > > forwarding multicast/broadcast in a loop-free manner? I think we do > > talk about most of that elsewhere, but it could be useful to tie that in > > with the tradeoffs that went into this decision. > > We added the following before the last sentence of the first paragraph (in > section 3.2): > > NEW: > "With the multilink subnet model, the routers have to take on > responsibility for tracking multicast state and forwarding multicast in > a loop-free manner." > > > (Does the "loop-free" part place any constraints on the IPv6 routing > > protocol(s) that can be used with IPv6 mesh over BLE?) > > Implicitly, yes. One comment here is that wireless multihop networks are > typically very dynamic (even if nodes are actually static), and therefore > it would not be unusual that even a routing protocol that is "loop-free" > may lead to temporary loops, the main point being that such loops (if any) > are expected to be just temporary. > > > Section 3.3.2 > > > > 1. A Bluetooth LE 6LN SHOULD register its non-link-local addresses > > with its routers by sending a Neighbor Solicitation (NS) message with > > the Extended Address Registration Option (EARO) and process the > > Neighbor Advertisement (NA) accordingly. Note that in some cases > > (e.g., very short-lived connections) it may not be worthwhile for a > > 6LN to send an NS with EARO for registering its address. However, > > the consequences of not registering the address (including non- > > reachability of the 6LN, and absence of DAD) need to be carefully > > considered. [...] > > > > Where can an exhaustive list of the consequences of not registering be > > found? > > It might also be helpful to give an example of something that a 6LN > > might do on such a very-short-lived connection where the non-link-local > > address is not registered (since, obviously, only link-local traffic > > would be possible). > > We discussed this comment with the WG. The outcome of the discussion was > using 'MUST' instead of 'SHOULD' in this paragraph, in order to avoid any > potential issues. > > > Section 3.3.3 > > > > To enable efficient header compression, when the 6LBR sends a Router > > Advertisement it MAY include a 6LoWPAN Context Option (6CO) [RFC6775] > > matching each address prefix advertised via a Prefix Information > > Option (PIO) [RFC4861] for use in stateless address > > autoconfiguration. Note that 6CO is not needed for context-based > > compression when context is pre-provisioned or provided by out-of- > > band means. > > > > I see that in RFC 7668 sending 6CO in this situation was MUST-level > > required. Is the reasoning behind the weakening of the requirement just > > the stated scenarios where pre-provisioned context renders the in-band > > context indication superfluous? If so, it might be possible to reword > > to be more clear about expectations. If not, some additional discussion > > of the reasoning might be helpful. > > Yes, the reasoning behind the weakening of the requirement is that > pre-provisioned or out-of-band-provided context renders the in-band > context indication superfluous. > > We added the following text to make the above more explicit: > > NEW: > Note that 6CO is not needed for context-based compression when context is > pre-provisioned or provided by out-of-band means, as in these cases the > in-band indication (6CO) becomes superfluous. > > > Section 8 > > > > connection with each 6LR (Step 3). After establishment of those link > > layer connections (and after reception of Router Advertisements from > > the 6LBR), Step 4, the 6LRs start operating as routers, and also > > initiate the IPSP Router role (note: whether the IPSP Node role is > > kept running simultaneously is an implementation decision). Then, > > > > (nit/editorial) The theme seems to be that "step N" is in parentheses > > after the description of the step, done everywhere except for step 4. > > So maybe " the 6LRs start operating as routers, and also initiate the > > IPSP Router role (Step 4) (note: whether the IPSP Node role is kept > > running simultaneously is an implementation decision)"? > > Agreed, and done in -10. > > Should you have any further comments, please let us know. > > Thanks, > > Carles (on behalf of the authors) > > > > > > _______________________________________________ > > 6lo mailing list > > 6lo@ietf.org > > https://www.ietf.org/mailman/listinfo/6lo > > > >
- [6lo] Benjamin Kaduk's Discuss on draft-ietf-6lo-… Benjamin Kaduk via Datatracker
- Re: [6lo] Benjamin Kaduk's Discuss on draft-ietf-… Carles Gomez Montenegro
- Re: [6lo] Benjamin Kaduk's Discuss on draft-ietf-… Benjamin Kaduk
- Re: [6lo] Benjamin Kaduk's Discuss on draft-ietf-… Carles Gomez Montenegro