Re: Updated IID length text

Fernando Gont <fgont@si6networks.com> Thu, 19 January 2017 06:01 UTC

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Subject: Re: Updated IID length text
To: Lorenzo Colitti <lorenzo@google.com>
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From: Fernando Gont <fgont@si6networks.com>
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Date: Thu, 19 Jan 2017 02:38:36 -0300
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On 01/19/2017 01:25 AM, Lorenzo Colitti wrote:
> On Thu, Jan 19, 2017 at 1:20 PM, Fernando Gont <fgont@si6networks.com
> <mailto:fgont@si6networks.com>> wrote:
> 
>     > It does make sense. /48 does impact things substantially. However, on
>     > like like wifi, the MAC address is the endpoint identifier, so if
>     > there's a duplicate MAC you can't get on the network.
> 
>     Could you please explain how you do the math such that in these two
>     scenarios:
> 
>     #1: SLAAC with 48-bit IIDs, where the IID is a random string of bits
>         (e.g. as resulting from RFC7217)
> 
>     #2: Traditional SLAAC with 64-bit IIDs, where the IID is generated from
>         a randomized MAC address (and in which, based on how MOdified EUI64
>         IIDs are generated, you have to embed the fixed 16-bit word 0xfffe
>         in the IID)
> 
> You forgot the "where layer 2 ensures that there are no duplicate MAC
> addresses on the network" part of this scenario.

1) AP != Network -- you might be assuming the network is simpler than it
really is

2) How many nodes do you need in a 48-bit space for the probability of
collisions to become a concern?

3) If you are concerned about collisions in 48 bits as a result of
random numbers, I'm curious why layer-3 concerns you more --
particularly when, in layer-3 you do have a mechanism for detecting
them, and one for recovering from them (whereas in layer-2, you don't).

Thanks,
-- 
Fernando Gont
SI6 Networks
e-mail: fgont@si6networks.com
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