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Re: 6MAN Adoption call on raft-chakrabarti-nordmark-6man-efficient-nd-04

Lorenzo Colitti <lorenzo@google.com> Thu, 09 January 2014 09:58 UTC

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From: Lorenzo Colitti <lorenzo@google.com>
Date: Thu, 09 Jan 2014 18:57:56 +0900
Message-ID: <CAKD1Yr03ZD3dDUpTWXUL_OiE_NYasUmpd9m1Ss6XoU0Qq_NCog@mail.gmail.com>
Subject: Re: 6MAN Adoption call on raft-chakrabarti-nordmark-6man-efficient-nd-04
To: Mikael Abrahamsson <swmike@swm.pp.se>
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On Thu, Jan 9, 2014 at 4:57 PM, Mikael Abrahamsson <swmike@swm.pp.se> wrote:

>
>  Why not? What's the downside of sending out an NS for an address that's
>> not there? You consume an ND cache slot for the incomplete entry, but if
>> you use the optimizations you'll always have enough space to avoid a DoS
>> scenario.
>>
>
> Because potentially this would cause hundreds or thousands of NS multicast
> packets on the LAN per second in a ddos scenario?
>

They would be rate-limited, just like any other ND packets on any
implementation worth its salt. I think an NS is 72 bytes including ICMPv6
header; if so, then even if you send out 500 of them per second, that's 36
kB/s. What sort of link has a problem carrying 36 kB/s? How many NSes per
second can routers send out anyway?


> If we can avoid the router having to learn anything by means of external
> packet triggers, I think it would be a big win.


Maybe in terms of bandwidth, but that's not free - you're trading off
bandwidth with state. The state has to be maintained, recovered on reboot,
synchronized between multiple routers, etc. etc., and that is brittle.

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