On Fri, 25 Mar 2011 01:30:48 -0300
Fernando Gont <ferna...@gont.com.ar> wrote:
> On 16/03/2011 01:51 p.m., Brian Haley wrote:
>
> > I have an almost off-topic comment, but since I've seen no mention of it
> > in any of these privacy threads...
> >
> > You have to assume in a large data center that almost every MAC address you
> > encounter is going to be randomly generated.
>
> Are they actually random? i.e., I'm curious about the algorithm used for
> generating the Interface IDs.
>
Here's the routine typically used under Linux to generate these types
of addresses -
include/linux/etherdevice.h
/**
* random_ether_addr - Generate software assigned random Ethernet
address
* @addr: Pointer to a six-byte array containing the Ethernet address
*
* Generate a random Ethernet address (MAC) that is not multicast
* and has the local assigned bit set.
*/
static inline void random_ether_addr(u8 *addr)
{
get_random_bytes (addr, ETH_ALEN);
addr [0] &= 0xfe; /* clear multicast bit */
addr [0] |= 0x02; /* set local assignment bit (IEEE802) */
}
>
> > This is because there are
> > *lots* of virtual machines out there, and the density of them is increasing
> > exponentially. Their MACs could change daily as they are deployed and
> > decommissioned, but from their perspective their MAC is hardware-based.
> > I know you have this as a "SHOULD" requirement, but figured I should mention
> > it since it's one of those places where this bit will be completely ignored.
>
> From the point of view of the VMs, they would still be using Modified
> EUI-64 Interface Identifiers. This is not that different from the case
> in which the admin sets the MAC address of an interface to some value
> that he wants (other than the *real* address of the interface). IMHO,
> this is out-of-scope for this document.
>
> Thanks!
>
> Best regards,
> --
> Fernando Gont
> e-mail: ferna...@gont.com.ar || fg...@acm.org
> PGP Fingerprint: 7809 84F5 322E 45C7 F1C9 3945 96EE A9EF D076 FFF1
>
>
>
>
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