[Gllug] Public IPs - When are they appropriate

[David Damerell]

On Wednesday, 14 Nov 2001, Paul Brazier wrote:
>>Even if we assume that the last 6 octets of the IPv6 address will be
>>the MAC address - so the unicast addresses effectively only offer
>>2^(125-48) addresses - 2^77 - that's still 1.5x10^23, or 5x 10^8 per
>>square meter of the Earth's surface.
>So does this mean that if you change your ethernet card you'll have to
>change your IPv6 address?

Yes and no. In practice, I imagine most user-level tools will obscure
this from you; you'll enter at most the other octets, and it'll change
magically.

>>[There's an obvious fallacy there in that not all those 2^77 devices
>>can have one of the 2^48 MAC addresses - but even if all devices have
>>a MAC address, 2^48 MAC addresses is 2.8 x 10^14. Which is probably
>>where this 'one per square meter' confusion comes from.]
>Maybe one MAC address would have several IPv6 addresses mapped to it?

It's possible - and note also the existence of IPv6 addresses that
refer to 'any interface of such-and-such a machine', rather than
specific interfaces.

[Also, of course, there's nothing magic about Ethernet.]

You might want to read the relevant RFC (2376?), since it knows more
than my rather casual acquaintance with the facts.

-- 
David Damerell <damerell at chiark.greenend.org.uk> flcl?

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