Re: [irtf-discuss] Why do we need to go with 128 bits address space ?

[Fernando Gont <[e-mail]>]

On 16/8/19 09:02, Roland Bless wrote:
> Hi Fernando,
> 
> see below.
> 
> On 15.08.19 at 20:13 Fernando Gont wrote:
>> On 15/8/19 12:27, Roland Bless wrote:
>> [....]
>>> c) given the increasing number of virtual machines and IoT devices 64
>>> bit isn't sufficient, see also the discussion of new MAC address lengths
>> [...]
>>
>> The MAC addresses should have never been embedded in the IID. In fact,
>> that's no longer the recommended way to generate IPv6 IIDs. See RFC8064.
> 
> I guess you misinterpreted my statement, since I
> was not referring to modified EUI64s or IIDs at all and I'm fully aware
> of the RFC.

Sorry for that!


> This was just to point to IEEE work on extending the MAC address space,
> showing the need for larger addresses and that 64-bit aren't obviously
> sufficient, see e.g.,
> https://www.ietf.org/proceedings/96/slides/slides-96-edu-ieee802work-0.pdf

My friend John would say that MAC addresses are not addresses: They
essentially are numeric IDs that are not topologically dependent (hence,
not addresses), and that are required to be globally unique (most of the
time, since you also have the U/L bit). The later can be convenient,
also it is not really a requirement per-se.

Assuming you could select a MAC address (well, "MAC ID") and detect
collisions, you probably wouldn't need much more than, say 16-bit MAC
addresses (unless you are really considering putting 65K devices on the
same broadcast segment).

>From that perspective, you might argue that we could have done with
96-bit addresses (not to say 80-bit addresses, or less) -- alignment
being a different business, of course. :-)  Or one could do
variable-length addresses

The specific 128-bit value seems to be a compromise between two
proposals
(https://www.lacnic.net/innovaportal/file/2578/1/ipv6-latnic2018-hinden-01.pdf)...
but I won't speak for Bob. ;-)

P.S.: Of course the ship has already sailed. So other than for the sake
of Internet history or the sake of discussion :-), there's no much of a
point in debating about the best address size, because we are not goin
to change it.
-- 
Fernando Gont
SI6 Networks
e-mail: [e-mail]
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