[Xen-devel] MAC address uniqueness

["James Harper" <JamesH@xxxxxxxxxxxxxxxx>]

FWIW, I assign my MAC addresses as "FE:FD:XX:00:YY:ZZ"

Where:
XX = what xen does to MAC addresses (00 in xen0, 01 in xenU)
YY = vmid (unique across all physical servers)
ZZ = interface number in xenU (00 = eth0, 01 = eth1)

Works for me!

Someone asked about trying to find a duplicate MAC address on a network
- it's pretty hard to do as the whole idea is that MAC addresses are
always assumed to me unique. Really really strange things happen if
they're not. The only real way to do it is if you have managed switches
and can check the MAC tables on each of the ports. The same MAC on more
than one port would indicate a dupe, except that you'd have to take a
series of snapshots as I think the switch would delete it from one port
of it saw it on another - it would tend to bounce around and that's what
you'd have to watch for.

I've just thought of another way, pinging an ip address with the
suspected duplicate mac should get you two responses (even if one of
them isn't an 'icmp echo response')

James


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