Re: IPv6 /64 links (was Re: ipv6 book recommendations?)

[Owen DeLong <owen () delong com>]

On Jun 19, 2012, at 8:44 AM, Alexandru Petrescu wrote:

> I think, the length of Interface ID be 64 is so mostly because IEEE
> works now with 64bit EUI identifiers (instead of older 48bit MAC
> addresses).  I.e. compatibility between IEEE and IETF IPv6 would be the
> main reason for this Interface ID to be 64.
>
> And this is so, even though there are IEEE links for which the MAC
> address is even shorter than 64bit, like 802.15.4 short addresses being
> on 16bit.  For those, an IPv6 prefix length of 112bit would even make
> sense.  But it's not done, because same IEEE which says the 15.4 MAC
> address is 16bit says that its EUI is 64bit. (what 'default' fill that
> with is what gets into an IPv6 address as well).

It's easy to put a 16 bit value into a 64 bit bucket.

It's very hard to put a 64 bit value into a 16 bit bucket.

Just saying.

> The good thing isthere is nothing in the RFC IPv6 Addressing
> Architecture that makes the Interface ID to be MUST 64bit.  It just says
> 'n'.
>
> What there _is_, is that when using RFC stateless addess
> autoconfiguration (not DHCP) and on Ethernet and its keen (WiFi,
> Bluetooth, ZigBee, more; but not USB nor LTE for example) then one must
> use Interface ID of 64bit; and consequently network prefix length of
> 64bit no more.

Well, there's another issue... On such a network, how would you go about
doing ND? How do you construct a solicited node multicast address
for such a node if it has, say, a /108 prefix?

Owen