> Can one of you network gurus explain how this is legal, by > Ethernet specs? > I'm a little out of date, but MAC addresses were supposed to > be sacrosanct physical IDs that are unique for each card. Of > course this was late 70's or early 80's, and there was no > danger of running out of them! Yes, that's true, they are supposed to be unique for every card, but some manufacturers have produced so many cards that they have had to repeat addresses. However, it is sometimes useful to be able to change them. For example, if you have a redundant firewall setup using the HA stuff for linux and one firewall fails and you have to switch over to the other one, you have to change the MAC addresses also to prevent any interruption in network service, at least when using cisco routers. It's also useful for when certain vendors have a software license that looks at the MAC address in your machine to be able to run. When that vendor charges 12 times as much for their NIC's with the new software license file, and you can get by with a $50 replacement NIC and use of the "ifconfig ethX hw ether <MAC>" commmand, it comes in very useful. You cannot however have two NICs with the same MAC on the same LAN at one time. You've been able to manually change the MAC address in IBM's AS/400 stuff for many years now. Jay