Virtual MAC/ IP Address calculation

Hi,

we are setting up a virtual server farm using xen virtualization.

Each instance needs to have an own ethernet and ip address. We'd like to use
the reserved range ACE:48 for the mac addresses.

I'm looking for a way to calculate the IP address from the mac address and
vice versa. For the ethernet address there are 3 bytes remaining but an
IP-address is 4 bytes long. Is there any compression algorithm or something
out there that can be used to solve this?

TIA -- Peter

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Peter Weiss wrote:

> Hi,
>
> we are setting up a virtual server farm using xen virtualization.
>
> Each instance needs to have an own ethernet and ip address. We'd like to
> use the reserved range ACE:48 for the mac addresses.
>
> I'm looking for a way to calculate the IP address from the mac address and
> vice versa. For the ethernet address there are 3 bytes remaining but an
> IP-address is 4 bytes long. Is there any compression algorithm or
> something out there that can be used to solve this?
>

If you're configuring your MAC addresses, why not just incorporate the last
three bytes of IP address as the last three bytes of the MAC? The first
byte of the IP address should be the same for your entire network, no
matter what IP address range you use, unless you've got more than 16
million "computers".

As for your question about an algorithm, it's impossible for 32 arbitrary
bits to be reduced to 24 bit numbers and be guaranteed that they're all
unique.

On Fri, 25 Nov 2005, in the Usenet newsgroup comp.os.linux.networking, in
article <(E-Mail Removed)>, Peter Weiss wrote:

>Each instance needs to have an own ethernet and ip address. We'd like to
>use the reserved range ACE:48 for the mac addresses.

[compton ~]$ etherwhois ACE:48
AC-DE-48 (hex) PRIVATE
ACDE48 (base 16)
[compton ~]$ zgrep -c ' PRIVATE$' MACaddresses.gz
79
[compton ~]$

It's not really "reserved" so much as assigned to an entity that has
requested IEEE not to publish their name and address. ('etherwhois' is a
local script that queries a copy of MACaddresses.gz obtained from IEEE
early in October.))

>I'm looking for a way to calculate the IP address from the mac address
>and vice versa. For the ethernet address there are 3 bytes remaining but
>an IP-address is 4 bytes long.

Grab a text book on how 'Multicast' works - the relationship between the
low 23 bits of 224.0.0.0/4 and 01:00:5e:

But why do you care? You're not going to be putting packets out onto
the Internet (because IANA hasn't assigned 0.0.0.0/0 to you), _AND_
that MAC addresses are "local" to the collision domain - once you hit
a router, they're meaningless. For that matter:

[compton ~]$ zgrep -c '^ACDE' MACaddresses.gz
1
[compton ~]$

>Is there any compression algorithm or something out there that can be
>used to solve this?

You wanna think about that for a minute? You have 4294967296 people you
want to give an individual number out of a pool of 16777216 Looks to
me that each number must be shared by 256 people. Ain't gonna work.

Old guy