Re: subnet prefix length > 64 breaks IPv6?

[Alexandru Petrescu <alexandru.petrescu () gmail com>]

Le 03/01/2012 23:36, Owen DeLong a écrit :
> 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.

I think that's right, sorry.  I mean - a reread of the PPPv6 RFC tells
that the Interface ID negotiated by PPP is stricly 64bit length.

(although it does refer to rfc4941 which specifically acks that "note
that an IPv6 identifier does not necessarily have to be 64 bits in length").

It's a mess :-)

Alex

> 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.