IPv6 /64 links (was Re: ipv6 book recommendations?)
Owen DeLong
owen at delong.com
Tue Jun 19 22:58:36 UTC 2012
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
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