Re: [v6ops] new draft: draft-yc-v6ops-solicited-ra-unicast

Erik Nordmark <nordmark@acm.org> Thu, 23 July 2015 16:26 UTC

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To: Owen DeLong <owen@delong.com>, Erik Nordmark <nordmark@acm.org>
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From: Erik Nordmark <nordmark@acm.org>
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Date: Thu, 23 Jul 2015 18:25:45 +0200
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Subject: Re: [v6ops] new draft: draft-yc-v6ops-solicited-ra-unicast
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On 7/23/15 1:14 AM, Owen DeLong wrote:
>
> Ole,
>
> Even on a flat wired L2 network I don't think it is harmful to default to unicast solicited RAs.
>
> If we take a worst case of 10000 hosts on the L2 network all rebooting/initializing at the same time, we will see:
> - 10000 DAD probes for link-local address
> - 10000 MLD joins for the solicited node MC for their link-locals
> As was pointed out earlier, we shouldn’t see MLD joins for LL solicited nodes or any other LinkScoped group, unless I am badly misunderstanding things.
Owen,
The RFC says to send them for everything but ff02::1 (all-nodes).
>
>> - 10000 RS messages(*)
>> - 1/10000 RA messages
> I think you mean 1 to 10000 because I don’t think fractional messages are possible.

Sorry for not explaining my notation. I meant 1 vs. 10000 depending on 
whether multicast or unicast RA is used.
Point is that the saving isn't that large given the other required 
packets during host interface initialization.

    Erik

>
>> - 10000 DAD probes for global addresses (N x 10000 if N prefixes on-link)
>> - N x 10000 mDNS etc type packets
>>
>> (*) RFC 4861 suggests receiving an RA before an RS is sent, thus under some timing conditions some RS messages might be avoided.
>>
>> But at best we seem to be talking about saving 20% of the packet during the boot of the 10000 hosts.
> True… However, even if this is an actual concern, we could consider a threshold in PPS where we send an RA Mcast response.
>
> e.g. if more than 10 RS received in 1 second, send a multicast RA.
>
> In fact, we could probably get away with delaying an RA response to RS for 250ms. If another RS arrives during that delay, respond multicast, else unicast.
>
> That probably still eliminates most of the RA traffic, may eliminate many of those 10000 RS messages, and could provide kind of the best of both worlds.
> I’m not sure how hard it would be to implement in silicon, however.
>
> Owen
>
>