[148117] in North American Network Operators' Group
Re: subnet prefix length > 64 breaks IPv6?
daemon@ATHENA.MIT.EDU (Owen DeLong)
Tue Jan 3 17:49:21 2012
From: Owen DeLong <owen@delong.com>
In-Reply-To: <CAPLq3UPzQaYmJX7ZBBySzSSdySdu1+75Rcb41JJoWuPLGniZwA@mail.gmail.com>
Date: Tue, 3 Jan 2012 14:36:54 -0800
To: Glen Kent <glen.kent@gmail.com>
Cc: nanog@nanog.org
Errors-To: nanog-bounces+nanog.discuss=bloom-picayune.mit.edu@nanog.org
On Dec 24, 2011, at 6:48 AM, Glen Kent wrote:
>>
>> SLAAC only works with /64 - yes - but only if it runs on Ethernet-like
>> Interface ID's of 64bit length (RFC2464).
>
> Ok, the last 64 bits of the 128 bit address identifies an Interface ID
> which is uniquely derived from the 48bit MAC address (which exists
> only in ethernet).
>
Not exactly. Most media have some form of link-layer addressing. For
Firewire, it's native EUI-64. For Ethernet, it's EUI-48 MAC addresses.
For token ring, I believe there are also EUI-48 addresses. For FDDI
(Remember FDDI?) I believe it was EUI-48 addresses. ATM and Frame
Relay also have EUI addresses built in to their interfaces (though I don't
remember the exact format and am too lazy to look it up at the moment).
>> SLAAC could work ok with /65 on non-Ethernet media, like a
>> point-to-point link whose Interface ID's length be negotiated during the
>> setup phase.
>
> If we can do this for a p2p link, then why cant the same be done for
> an ethernet link?
>
I'm not so sure the statement above is actually true.
Owen
> Glen
>
>>
>> Other non-64 Interface IDs could be constructed for 802.15.4 links, for
>> example a 16bit MAC address could be converted into a 32bit Interface
>> ID. SLAAC would thus use a /96 prefix in the RA and a 32bit IID.
>>
>> IP-over-USB misses an Interface ID altogether, so one is free to define
>> its length.
>>
>> Alex
>>
>>>
>>> Regards, K.
>>>
>>
>>
