On Apr 5, 2010, at 5:08 PM, Valdis.Kletnieks@vt.edu wrote:
On Mon, 05 Apr 2010 16:36:26 EDT, Jon Lewis said:
Since they only really need to be unique per broadcast domain, it doesn't really matter. You can I could use the same MAC addresses on all our home gear, and never know it. For manufacturers, it's probably reasonably safe to reuse MAC addresses they put on 10mbit ISA ethernet cards...if they were a manufacturer back then.
Until you buy 25 cards with the same MAC address and deploy them all across your enterprise
I don't think that's possible given that Jon was suggesting. I'm 3COM, I made ISA 10Base2 / 10Base5 cards in the 90s. I run out of MAC addresses. Instead of going to get more - if I even can! - I recycle those MAC addresses, figuring the 10GE PCI-X cards I'm making now have 0.000% chance of being on the same b-cast domain as one of those old ISA cards. Even if I am wrong, the max collision possibility is 2, not 25. Seems reasonable. If I am wrong, I'll apologize profusely, refund the price of the 10G card I gave the customer, ship him a new one free, so he gets two he can use (assuming he has more than one b-cast domain), which would probably make the customer happy. Wanna bet how many times 3COM would have to ship free 10GE cards? -- TTFN, patrick
- the problem can go un-noticed for *weeks* as long as two boxes aren't squawking on the same subnet at the same time(*). Of course, you never stop to actually *check* that two cards in different machines have the same address, because That Never Happens, and you spin your wheels trying to figure out why your switching gear is confused about the MAC addresses it's seeing (and it always takes 3 or 4 tickets before one actually includes the message "Duplicate MAC address detected" in the problem report..)
(*) And as Murphy predicts, whenever it happens, one of the two offenders will give up in disgust, power off the machine, and go on coffee break so the arp cache has timed out by the time you start trying to work the trouble ticket. ;)
(Yes, we're mostly older and wiser now, and more willing to include "the damned hardware is posessed by an Imp of Perversity" in our troubleshooting analysis. Had an SL8500 tape library last week that reported 'Drive State: Unpowered' and 'Drive Status: Not Communicating' and still reported 'Drive Health: Good'.