Re: [Roll] enrollment priority
Michael Richardson <mcr+ietf@sandelman.ca> Wed, 29 April 2020 12:40 UTC
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From: Michael Richardson <mcr+ietf@sandelman.ca>
To: Routing Over Low power and Lossy networks <roll@ietf.org>
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Date: Wed, 29 Apr 2020 08:40:45 -0400
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Subject: Re: [Roll] enrollment priority
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{sorry, this email sat unsent for too long} Rahul Jadhav <nyrahul@outlook.com> wrote: >> Consider the following scenario (the attached image will help explain): >> Node C's preferred parent is node B and alt parent is node A. What >> happens if the min-priority of node B changes to 127 after the node C >> has joined the network with B as a preferred parent? I am assuming >> that the min-priority impacts only the newly joining nodes i.e., once >> node B changes the priority to 127 then node C also changes the >> priority to 127 and thus no new nodes join. However, the change in >> node B's min-priority may not impact node C's decision to continue >> using node B as the preferred parent (?). What happens when node C has >> alternate parent node A whose priority is lesser than 127. Should node >> C switch to node A so as to allow new downstream nodes to join the >> network? mcr> First, I think that if node C had a MP of 127, then it would *NOT* advertise mcr> itself as a Join Proxy. RJ> Consider non-6tisch case, where the 6LR's resources are full and does RJ> not want any new nodes to connect to it. In this case, it still needs RJ> to advertise its DIO for all the existing nodes which have already RJ> joined through it. The new nodes will see MP=127 and hence won't RJ> join. But the gist is, Node C has to keep advertising for all its RJ> existing nodes. It cannot stop sending DIOs. Okay, so I think that we have further confusion of Join (DODAG thing) vs Enroll (onboarding thing) :-) I have taken another pass through the document to make sure that all uses of join, other than "Join Proxy" now say Enroll. mcr> So if it was sending Enhanced Beacons, then it mcr> would: mcr> a) set proxy prio to 0x7f. mcr> b) maybe even stop sending EBs [have to think about this] RJ> Not sure in case of 6tisch too if it can stop sending EBs? Since it RJ> may be needed for existing nodes who have already joined. Yes, it probably needs to continue sending EBs. mcr> If node C *does* change to node A, then it would change it's priority. mcr> But it has to do that, and maybe there are reasons why A won't accept it. RJ> Sure node A might have its own reasons to not accept it, but the MP RJ> suggests that it is willing to accept node C. The problem is when RJ> node C switches to Node A, the whole sub-DODAG rooted at C switches RJ> and this may result in node A's MP to reach 127. Since node B is now RJ> free, it's MP value will decrease. This can result in oscillations in RJ> the network. Agreed. The fundamental problem is that the sub-DODAG needs to be split. I don't think that we can do that in this option or in EBs. It has to be done in DIOs and DAO-ACKs and... I think that we have had proposals to deal with this before (what happened to them?) > 6LRs that support this option, but whose parent does not send it SHOULD > assume a value of 0x40 as their base value. > The nodes adjust this base value based upon their observed congestion, > emitting their adjusted DIO value to their children. > (0x40 is my wet-finger-in-the-air, seat-of-the-pants guess) RJ> Consider that a 6LR who does not support MP gets a DIO with RJ> MP=127. The 6LR will ignore the MP field and sends it DIO without MP RJ> and the downstream nodes will assume an MP of 0x40! This may be a RJ> problem. I added some analysis to my slides today to deal with this. I am open to other values, but I think we need to pick some value. Maybe 0, but I think not. Maybe rank * VALUE. >> We tried working on a problem-statement in the past in LWIG [1] which >> talked about how to handle the case where some upstream nodes cache >> (routing/neighbor) is full and how would it stop the new downstream >> nodes to attach in that path. Enrollment priority was referenced as a >> possible solution. > Good. Would more informative cross-references help? > Do you want to co-author? RJ> Yes, I would love to work on this problem statement. https://github.com/roll-wg/draft-ietf-roll-enrollment-priority I will unicast to get permissions right. -- Michael Richardson <mcr+IETF@sandelman.ca>, Sandelman Software Works -= IPv6 IoT consulting =-
- [Roll] enrollment priority Rahul Jadhav
- Re: [Roll] enrollment priority Michael Richardson
- Re: [Roll] enrollment priority Rahul Jadhav
- Re: [Roll] enrollment priority Michael Richardson
- Re: [Roll] enrollment priority Michael Richardson