[EMAIL PROTECTED] wrote: >Not really plan9 specific, but >1. does anybody know if and how MAC addresses are allocated to network >card manufacturers? >2. do manufacturers guarantee the uniqueness of MAC addresses they build? >3. is it still true (was it ever true), that if I bought 2 NIC's, >they'll have different MAC addresses? >4. is it the responsibility of the OS to override the default MAC >address if another card with the same (possibly overriden) MAC address >was present on the LAN? > > thanks: gergo > > Well, since my company makes network cards, I can probably help you here! ;-) Each vendor registers one or more 3 octet OUIs from the IEEE, which is used as the first 3 octets of a MAC address. The remaining 3 are up to the vendor to use. Theoretically, all MAC addresses are supposed to be unique. For one vendor code you only have 16 million addresses available, so there is the possibility of wrap around with MAC addresses -- it's up to the vendor to comply. (Once you have a practical deployed base of 90%, you can request a new OUI.) For all practical purposes, you can assume that MAC addresses are unique.
For this part here is a good tutorial: http://standards.ieee.org/regauth/oui/tutorials/lanman.html As to question 4, nope. The OS has no good way of determining a new MAC address to override to (The OS doesn't have an OUI, and then how do you pick the serial number after that??), and it's not considered a real problem because of the uniqueness of MACs. Not to mention you don't even want to think about how a switch could get confused by the whole situation... :-) Mike
