From ​The Xen User Guide:

"… MAC address from the range 00:16:3E:xx:xx:xx, assigned by IEEE to XenSource as an OUI (organizationally unique identifier). XenSource Inc. gives permission for anyone to use addresses randomly allocated from this range for use by their Xen domains."

mac	ip	notes
00:16:3E:00:00:01	10.50.71.10	console.vgrid1 eth0
00:16:3E:00:00:02	10.71.0.10	console.vgrid1 eth1
00:16:3E:00:00:03	10.50.72.10	console.vgrid2 eth0
00:16:3E:00:00:04	10.72.0.10	console.vgrid2 eth1
00:16:3E:00:00:05	10.50.73.10	console.vgrid3 eth0
00:16:3E:00:00:06	10.73.0.10	console.vgrid3 eth1
00:16:3E:00:00:07	10.50.74.10	console.vgrid4 eth0
00:16:3E:00:00:08	10.74.0.10	console.vgrid4 eth1
00:16:3E:00:00:09	10.0.0.17	internal7 eth0