Re: [6lowpan] FW: TID in ARO [was: "Advertize on Behalf" flag in ARO]
Erik Nordmark <nordmark@acm.org> Thu, 21 April 2011 21:39 UTC
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Date: Thu, 21 Apr 2011 14:40:18 -0700
From: Erik Nordmark <nordmark@acm.org>
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Subject: Re: [6lowpan] FW: TID in ARO [was: "Advertize on Behalf" flag in ARO]
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On 4/21/11 7:30 AM, nicolas.riou@schneider-electric.com wrote: > > Hi Erik, > > Comments in line... > > > From: Erik Nordmark [mailto:nordmark@acm.org] > > Sent: Thursday, April 21, 2011 1:25 AM > > To: nicolas.riou@schneider-electric.com > > Cc: Pascal Thubert (pthubert); 6lowpan@ietf.org; Dijk, Esko > > Subject: Re: [6lowpan] FW: TID in ARO [was: "Advertize on Behalf" flag in > > ARO] > > > > On 4/20/11 1:21 AM, nicolas.riou@schneider-electric.com wrote: > > > > > > Dear Pascal and al, > > > > > > I support the idea of reviving the TID in ARO and DAR/DAC. Supporting > > > a TID directly in the node initiating the initial NS appears much > > > simpler than time stamping in the parent router. > > > > How would you make this work if the protocol between the routers is not > > RPLv1, but some future version of RPL or a completely different routing > > protocol? > > As Pascal answered in his post, the TID is not particularly coupled with > RPLv1. The TID is just an extra information provided by the node during > ND registration which dramatically simplifies node localization but also > enable DAD across a backbone of Edge Routers advertizing the same prefix. > Which alternative solution would you suggest for DAD? DAD works fine with what we have in ARO. If the same EUI-64 (re)registers the same IPv6 address, then it is not a duplicate. If a different EUI-64 tries to registers an IPv6 address (already registered with some other EUI-64), then it is a duplicate. That is independent whether the check is done in a 6LR or 6LBR. What do you see as the problem with DAD? Can you provide an example of what doesn't work with 6lowpan-nd? > The TID can fit in "reserved" field of ARO/DAR/DAC and thus can come > at no cost. FWIW Complexity is the true cost, because unneeded complexity leads to non-interoperability for no benefit. > Thanks to the lollipop mechanism defined in 6lowpan-nd-07 the TID can be > implemented even in the most constrained devices which might not be able > to consistently increment the TID. The lollipop stuff is not proven technology. It existed in an early draft of OSPF, and was replaced. I assume it was replaced for a reason. Any proven TID scheme would require stable storage on the device, so that the device doesn't accidentally reuse old TIDs too soon. I don't think we want to require that capability on all 6lowpan hosts, just because it is perceived too hard to have RPL keep track of things. Erik > Regards, > Nicolas > > > > The decoupling of the host-router interaction from router-router > interaction > > has served us well in the history of the Internet. > > > > Erik > > > > > A simple and efficient method to detect mobility of hosts along a > > > backbone of Edge Routers is an important feature to deploy backbones > > > of Edge Routers in Buildings and should be clarified before closing > > > 6LoWPAN WG. > > > > > > Cheers, > > > Nicolas > > > > > > > > > > > > > > > > > > > > > *"Pascal Thubert (pthubert)" <pthubert@cisco.com>* Envoyé par : > > > 6lowpan-bounces@ietf.org > > > > > > 18/04/2011 10:37 > > > > > > > > > A > > > "Dijk, Esko" <esko.dijk@philips.com>, "Erik Nordmark" > > > <nordmark@acm.org> cc > > > 6lowpan@ietf.org > > > Objet > > > Re: [6lowpan] FW: TID in ARO [was: "Advertize on Behalf" flag in > > ARO] > > > > > > > > > > > > > > > > > > > > > > > > > > > Hi Esko, Erik > > > > > > The discussion on RPL and hosts should happen on the RPL list under a > > > different topic. The point being discussed here is this: > > > > > > The reality is also that those (LLN) networks will need to scale to > > > large subnets in plants, building, etc... (see the requirement drafts > > > in ROLL). Registering to all LBRS is totally impractical. 6LoWPAN ND > > > requires a coordination between LBRs but does not say how it happens. > > > This problem was discussed in 6LoWPAN; the answer was in ND-01to07; > > > and it requires a TID, for the same reason as RPL. Removing the > > > backbone operation and the TID from the draft is ostrich policy. > > > > > > BTW 6LoWPAN ND needs a TID to correlate the NS and the NA as all other > > > registrations do when strict ordering is not guaranteed (MIP being an > > > example). Say that due to some config, a node registers a lifetime of > > > X, then deregisters (lifetime 0), then reregisters (lifetime X) in a > > > rapid sequence, but does not get an answer yet. Then it finally gets 2 > > > AROs back, lifetime X and 0. What's the final state in the router? > > > > > > I'd like to hear what others think. > > > > > > Pascal > > > http://www.xtranormal.com/watch/7011357/ > > > > > > > > > > -----Original Message----- > > > > From: Dijk, Esko [mailto:esko.dijk@philips.com] > Sent: Monday, > > > April 18, 2011 10:19 AM > To: Erik Nordmark; Pascal Thubert > > > (pthubert) > Cc: 6lowpan@ietf.org > Subject: RE: [6lowpan] FW: TID > > > in ARO [was: "Advertize on Behalf" flag in > ARO] > > Hello Erik, > > > > > taking the definition you quoted: > > > > 'host' refers to an LLN device that can generate but does not > > > forward > RPL traffic > > the question may arise what is "RPL > > > traffic"? It is not defined in the RPL draft > it seems. Pascal > > > clarified to me it is traffic associated to a RPL instance, not > > > > necessarily RPL protocol messages. This means that a host could > > > generate > RPL traffic without being aware of the existence of RPL at > > > all. So, _not_ all > hosts have to speak RPL? > > > > The RPL draft does not explicitly state if "hosts" in a RPL network > > > always > speak RPL, never speak RPL, or can be mixed RPL/non-RPL > > > speakers. > > > > > > > > Taking the definition of 'node' in the RPL draft: > > > > 'node' refers to any RPL device, either a host or a router > > > > > rules out (?) the option that all "hosts" are non-RPL speakers, since > > > there > may be a "RPL device" (i.e. RPL-speaking device, I assume) > > > that is also a host. > > > > > > > > I communicated these perceived unclarities to Pascal and the RFC > > > editor 2 > weeks ago. Once this is clear I think the present > > > discussion can continue. > > > > And then there is the related discussion of ND support for sleepy > > > devices, > the original topic of Anders ;) > > best regards, > > > > > Esko > > > > -----Original Message----- > From: > > > 6lowpan-bounces@ietf.org [mailto:6lowpan-bounces@ietf.org] On > > > > Behalf Of Erik Nordmark > Sent: Friday 15 April 2011 18:39 > To: > > > Pascal Thubert (pthubert) > Cc: 6lowpan@ietf.org > Subject: Re: > > > [6lowpan] FW: TID in ARO [was: "Advertize on Behalf" flag in > ARO] > > > > > On 4/14/11 11:43 PM, Pascal Thubert (pthubert) wrote: > > > > > > > > > RPL can do what all classical IGPs can do WRT hosts. That is as > > > long > > as the host address belongs to the router's prefix and stays > > > attached > > to that router. > > > > > > > > I just realized that we might be talking about a different > > > definition of "host". > > > > What I mean by "host" is a node which does not participate in a > > > routing > protocol, and does not forward packets (except packets > > > explicitly addressed > to itself using e.g., a routing header). > > > > > > > > However, RPL has a different definition: > > > > 'host' refers to an LLN device that can generate but does not > > > forward > RPL traffic > > Basically per the RPL definition there is > > > no such thing as a node which does > not participate in the RPL > > > protocol. > > > > IMHO what is in RPL should have been defined as a non-forwarding > > > node, so > that we can have a sane discussion without getting > > > entangled in terminology > issues. > > > > > > > > Which definition of "host" are you using above? > > > > > > > > Per the RPL definition there is no need for 6lowpan-nd, since all > > > nodes will > speak RPL. This is rather confusing, don't you think? > > > > > > > > Erik > > > > > > > > > When the topology becomes multilink subnet and mobility is > > > required > > then it is a new problem entirely, and NO, 4861 is not a > > > suitable > > interaction with the router to allow the router to > > > redistribute a host route. > > > > > Because the neighbor cache that 4861 builds is not a of the same > > > > > nature as the binding table that 6LoWPAN ND builds. Another thing > > > that > > 6LoWPAN ND fails to express correctly. I proposed text to > > > explain that > > (attached) but it was not considered, contributing > > > to the illusion > > that a cache is a table. > > > > > > > > > > The reality is also that those networks will need to scale to > > > large > > subnets in plants, building, etc... (see the requirement > > > drafts in > > ROLL). Registering to all LBRS is totally impractical. > > > 6LoWPAN ND > > requires a coordination between LBRs but does not say > > > how it happens. > > > > > This problem was discussed in 6LoWPAN; the answer was in > > > ND-01to07; > > and it requires a TID, for the same reason as RPL. > > > Removing the > > backbone operation and the TID from the draft is > ostrich > > policy. > > > > > > > > > > RPL already adapted to the new reality of large multilink subnet > > > with > > inner mobility. Placing the blame on RPL is another > > > illusionist trick. > > > > > And this is not RPL last call. > > > > > > > > > > BTW 6LoWPAN ND needs a TID to correlate the NS and the NA as all > > > other > > registrations do when strict ordering is not guaranteed > > > (MIP being an > > example). Say that due to some config, a node > > > registers a lifetime of > > X, then deregisters (lifetime 0), then > > > reregisters (lifetime X) in a > > rapid sequence, but does not get an > > > answer yet. Then it finally gets > > > 2 > > > > > AROs back, lifetime X and 0. What's the final state in the router? > > > > > > > > > > It seems we can never agree on any of this. I'd like to hear what > > > > > others think. > > > > > > > > > > Pascal > > > > > http://www.xtranormal.com/watch/7011357/ > > > > > > > > > > > > > > >> -----Original Message----- > > > > >> From: 6lowpan-bounces@ietf.org [mailto:6lowpan- > > bounces@ietf.org] > > > On > >> Behalf Of Erik Nordmark > >> Sent: Friday, April 15, 2011 > > > 1:30 AM > >> To: 6lo>> '6lowpan' > > > > >> Subject: Re: [6lowpan] Fwd: Re: "Advertize on Behalf" flag in > > > ARO > >> > >> > >> On 4/13/11 12:53 AM, Pascal Thubert (pthubert) > > > wrote: > > > > >>> Hi Erik: > > > > >>> > > > > >>> The RPL (DAO) sequence number allows the node to increment > > > rapidly > >>> in case of rapid changes and then lazily when the > > > situation is > >>> stable and DAO are scarce. The increase is > > > strictly monotonous which > > > >>> is critical to us. > > > > >>> > > > > >>> A time stamp imposes a synchronization between the routers. We > > > do > >>> not have such mechanism in RPL. A time unit (a granularity) > > > must be > >>> agreed upon. Within that unit, movements go undetected > > > so the time > >>> unit must be thin grained to cover rapid changes. > > > Yet, depending on > >>> the medium, the time unit, and the size of > > > the network, it is not > >>> necessarily easy/possible to guarantee a > > > strictly monotonous value > >>> with a thin grained time unit. And we > > > have limited space (2 > > > octets) > > > > >>> and have to deal with wrap around, which divides the space by > > > at > > least 3. > > > > >>> > > > > >>> So RPL went for a sequence number. > > > > >> > > > > >> But the unstated assumption that RPL made is that all > > > host-to-router > >> protocols have to now be RPL aware. That doesn't > > > sound like good > > design. > > > > >> A host isn't aware of whether the routers speak IS-IS or OSPF, > > > so why > >> do the hosts need to be aware of RPL by passing some TID > > > around? > > > > >> > > > > >>> I think ND has the same need as MIP for a TID == Sequence # . > > > We > >>> know of MIP; We know of RPL. We know of the backbone router > > > > >>> operation. We know we'll need the TID and we know exactly why. I > > > > >>> think we should have it in the 6LowPAN ND spec right away to > > > avoid > >>> interop issues when we add RPL and BR operations. > > > > >> > > > > >> I don't see a need in 6lowpan-nd for a TID; the protocol works > > > fine > > without it. > > > > >> I think RPL needs to be improved to deal with reality. Isn't > > > there a > >> desire for RPL to handle 4861 hosts? Those would never > > > know about a > > TID. > > > > >> > > > > >> Erik > > > > >> > > > > >> _______________________________________________ > > > > >> 6lowpan mailing list > > > > >> 6lowpan@ietf.org > > > > >> https://www.ietf.org/mailman/listinfo/6lowpan > > > > > _______________________________________________ > > > > > 6lowpan mailing list > > > > > 6lowpan@ietf.org > > > > > https://www.ietf.org/mailman/listinfo/6lowpan > > > > > > > > > > > > > _______________________________________________ > > > > 6lowpan mailing list > > > > 6lowpan@ietf.org > > > > https://www.ietf.org/mailman/listinfo/6lowpan > > > > > > > > The information contained in this message may be confidential and > > > legally > protected under applicable law. The message is intended > > > solely for the > addressee(s). If you are not the intended recipient, > > > you are hereby notified > that any use, forwarding, dissemination, or > > > reproduction of this message is > strictly prohibited and may be > > > unlawful. If you are not the intended recipient, > please contact the > > > sender by return e-mail and destroy all copies of the > original > > > message. > > > > > > _______________________________________________ > > > 6lowpan mailing list > > > 6lowpan@ietf.org > > > https://www.ietf.org/mailman/listinfo/6lowpan > > > > > > > > __________________________________________________________ > > ____________ > > > This email has been scanned by the MessageLabs Email Security System. > > > > > __________________________________________________________ > > ____________ > > > > > > > > >
- [6lowpan] FW: TID in ARO [was: "Advertize on Beha… Pascal Thubert (pthubert)
- Re: [6lowpan] FW: TID in ARO [was: "Advertize on … Erik Nordmark
- Re: [6lowpan] FW: TID in ARO [was: "Advertize on … Pascal Thubert (pthubert)
- Re: [6lowpan] FW: TID in ARO [was: "Advertize on … Erik Nordmark
- Re: [6lowpan] FW: TID in ARO [was: "Advertize on … Erik Nordmark
- Re: [6lowpan] FW: TID in ARO [was: "Advertize on … Pascal Thubert (pthubert)
- Re: [6lowpan] FW: TID in ARO [was: "Advertize on … Pascal Thubert (pthubert)
- Re: [6lowpan] FW: TID in ARO [was: "Advertize on … nicolas.riou
- Re: [6lowpan] FW: TID in ARO [was: "Advertize on … Geoff Mulligan
- Re: [6lowpan] FW: TID in ARO [was: "Advertize on … Pascal Thubert (pthubert)
- Re: [6lowpan] FW: TID in ARO [was: "Advertize on … Geoff Mulligan
- Re: [6lowpan] FW: TID in ARO [was: "Advertize on … Erik Nordmark
- Re: [6lowpan] FW: TID in ARO [was: "Advertize on … Pascal Thubert (pthubert)
- Re: [6lowpan] FW: TID in ARO [was: "Advertize on … Pascal Thubert (pthubert)
- Re: [6lowpan] FW: TID in ARO [was: "Advertize on … Pascal Thubert (pthubert)
- Re: [6lowpan] FW: TID in ARO [was: "Advertize on … Erik Nordmark
- Re: [6lowpan] FW: TID in ARO [was: "Advertize on … Erik Nordmark
- Re: [6lowpan] FW: TID in ARO [was: "Advertize on … Wassim Haddad
- Re: [6lowpan] FW: TID in ARO [was: "Advertize on … Pete St. Pierre
- Re: [6lowpan] FW: TID in ARO [was: "Advertize on … Basavaraj.Patil
- Re: [6lowpan] FW: TID in ARO [was: "Advertize on … Behcet Sarikaya