Re: [Efficientnd-dt] Food for thought - router-controlled RS refresh
Erik Nordmark <nordmark@sonic.net> Tue, 11 November 2014 06:01 UTC
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Date: Mon, 10 Nov 2014 22:01:35 -0800
From: Erik Nordmark <nordmark@sonic.net>
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To: Lorenzo Colitti <lorenzo@google.com>, Erik Nordmark <nordmark@acm.org>
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Subject: Re: [Efficientnd-dt] Food for thought - router-controlled RS refresh
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On 11/10/14 8:09 PM, Lorenzo Colitti wrote: > On Wed, Aug 20, 2014 at 9:34 PM, Erik Nordmark <nordmark@acm.org > <mailto:nordmark@acm.org>> wrote: > > Do folks think this is a reasonable starting point for some Design > Team output when it comes to RS/RA? > If so, should we include all the RS/RA pieces in one document? > (implementation advise, raise the max advinterval, etc) > > > Finally found the time to take a look. I'm a bit concerned by the > following issues: > > 1. If sleepy nodes are free to ignore multicast RAs, that means that > it's no longer possible for the network to give hosts updated > configuration in a timely manner. This is a regression in > functionality that we should consider carefully. To my mind, if a host > is available to receive unicast packets, then it should also listen to > multicast RAs. I forgot the terms we used to distinguish between hosts that wake up based on packets and those that wake up based on their timer. But the latter would receive neither unicast and multicast when asleep. That doesn't mean that the network admin has no control. The Refresh Time in the RTO places an upper bound on the time it takes to push out new information. Example - At time=0 a RA with RTO=60 minutes is sent out - might be unicast in response to a RS from a sleepy node. - At time=1 minute something changes and the router multicasts an RA with some changes - but sleepy node is not awake (Presumably this RA retransmitted a few times per RFC 4861 to make non-sleepy nodes more likely to receive it) - Suppose sleepy node wakes up at time=40 minutes, then it will not send a RS refresh (it has 20 minutes left). But before t=60 minutes it will send a RS refresh and receive the changed information. - Suppose the node wakes up at time=70 minutes, then it will immediately send a RS refresh. Thus in the worst case the RTO refresh time is an upper bound on the time it takes to push out new information. But if the RTO refresh time is less than the sleep time for the sleepy nodes, then the sleepy nodes would always refresh on wakeup. > > 2. If periodic RAs are turned off, then "legacy" hosts will lose > connectivity. That seems bad. The current spec allows a maximum router > lifetime of 9000 seconds, right? If so, then operators today can > already set the RA period to something like 4450 seconds, which allows > the hosts to miss one RA without losing connectivity. Is one packet > every 75 minutes that bad? The issue for hosts that sleep on a schedule is that they don't want to have an active receiver hence they can't receive a packet sent at some unknown point in time; requires having the receiver turned on all the time, or having some router/AP which queues packets reliably until they wake up. Another concern was around the paging cost in cellular networks that is triggered by sending periodic packets to all hosts (we discussed a draft about this in Toronto). If instead the host wakes up and send a packet (an RS) it means that the network state has been established to know the hosts current base station etc. Those are two different cases where the router initiated RA doesn't work well. Erik > > Cheers, > Lorenzo
- [Efficientnd-dt] Food for thought - router-contro… Erik Nordmark
- Re: [Efficientnd-dt] Food for thought - router-co… Erik Kline
- Re: [Efficientnd-dt] Food for thought - router-co… Erik Nordmark
- [Efficientnd-dt] Food for thought - router-contro… Erik Nordmark
- [Efficientnd-dt] today's call Jouni
- Re: [Efficientnd-dt] Food for thought - router-co… Samita Chakrabarti
- Re: [Efficientnd-dt] Food for thought - router-co… Andrew Yourtchenko
- Re: [Efficientnd-dt] Food for thought - router-co… Erik Nordmark
- Re: [Efficientnd-dt] Food for thought - router-co… Erik Nordmark
- Re: [Efficientnd-dt] Food for thought - router-co… Lorenzo Colitti
- Re: [Efficientnd-dt] Food for thought - router-co… Erik Nordmark