subnet prefix length > 64 breaks IPv6?

Owen DeLong owen at delong.com
Tue Jan 3 22:36:54 UTC 2012


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.
>>> 
>> 
>> 





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