Re: draft-gont-6man-managing-privacy-extensions-00.txt

On Fri, 25 Mar 2011 01:30:48 -0300
Fernando Gont <fernando@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: fernando@gont.com.ar || fgont@acm.org
> PGP Fingerprint: 7809 84F5 322E 45C7 F1C9 3945 96EE A9EF D076 FFF1
> 
> 
> 
> 
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