Re: IPv6 prefixes longer then /64: are they possible in DOCSIS networks?

[Bill Stewart <nonobvious () gmail com>]

On Wed, Nov 30, 2011 at 1:18 PM, Mark Blackman <mark () exonetric com> wrote:
> ... and I'm not sure why SLAAC wanted more than 48 bits.

One reason IPv6 addresses are 128 bits long instead of 40, 48, 64 or
80 is because converting from IPv4 to IPv6 is really painful and we
don't want to ever have to do it again in the future.

Eventually we will run out of 48-bit MAC addresses, because we'll run
out of 24-bit manufacturer ID parts, and we'll transition to EUI-64 or
something like it.  It will be ugly and painful, and it will break
many things, and if we used 48-bit MAC addresses for SLAAC, it would
break IPv6 as well.  Using EUI-64 instead of MAC means that all the
breakage will live at Layer 2.

It does break some things in IPv6 - we've spent a couple of years
arguing about whether ISPs should give customers /48, /56, /60, or
/64, instead of having the nice clean "64 bits for the network
provider, 16 bits for subnet, 48 for MAC" that the earlier proposals
adapted from Netware IPX, but that would probably have gotten us in
trouble also.

I can't explain why EUI-64 picked its particular ugly way to convert
48-bit MACs to 64-bit, but I won't rant about that here.


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             Thanks;     Bill

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