[Gllug] Public IPs - When are they appropriate

[Richard Cottrill]

I have some bad news for you here. You may be talking rubbish ;)

To the best of my knowledge IPv6 has always been intended as a 'drop-in'
replacement for IPv4, so all of the things that you can do to/with IPv4
should be possible in v6. Included in the list of things to do are multiple
IP addresses per MAC address (per computer).

The problem with having more MAC than IP addresses isn't that you can't have
multiple IP addresses per NIC, it's more that you might have multiple NICs
per MAC address. This is only a problem on subnets - and even then I don't
think it's catastrophic, the OS should just have to discard packets that
have the wrong IP address. Switches would have to be programmed with the
expectation that MAC addresses aren't unique, etc. Not the end of the world,
but much less efficient in the highly unlikely case that two irreplaceable
NICs (a contradiction in terms for mine) have the same MAC address on the
same indivisible subnet (another contradiction).

As an example of 1:M MAC to IP addresses on a network: the multicast spec
includes a range of MAC addresses to be used for multicast packets. The
mapping of multicast groups to the range of MAC addresses they have isn't
1:1 but it does form an effective low level filter for the vast majority of
traffic.

Potentially there could be a similar situation even for point-to-point comms
without the Earth swallowing up civilisation as we know it...

Richard
(corrections appreciated)

> -----Original Message-----
> From: gllug-admin at linux.co.uk [mailto:gllug-admin at linux.co.uk]On Behalf
> Of Paul Brazier
> Sent: Wednesday, November 14, 2001 1:49 PM
> To: gllug at linux.co.uk
> Subject: RE: [Gllug] Public IPs - When are they appropriate

<snip>

> Maybe one MAC address would have several IPv6 addresses mapped to it?
> Like if you have a single machine using IP virtual hosting. I think the
> popularity of name-based virtual hosting came about because of the
> shortage of IP addresses?
>
> (Forgive me if I'm taking rubbish again ;))


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