: >> Or just make one up.... : >
: > It's a disaster waiting to happen. IMHO, this : > is not an option. : >
: > Besides, the invented address must conform to the : > Ethernet addressing rules, so hi-jacking is by far : > the easiest way, given the price of abandoned NICs.
: Ethernet reserves the least significant bit in the first byte for multicast : addresses (01-00-00-00-00-00). There are no other Ethernet addressing : restrictions.
The second least sig bit of the first byte is also reserved for indicating administratively set MAC addresses. All allocated mac ranges have that bit set to 0. Those with long memories and networks running decnet will remember the administratively set "AA........" mac addresses decnet created.
If you invent a MAC address - set this bit.
: Given that MAC addresses are 48 bits long and only 1 bit is reserved for : multicast addresses, there are total of 2^47-1 possible unicast addresses. : Subnets normally consist of 253 or less computers, so there is an extremely : good probability that a random unicast address will not conflict with : already existant or future equipment. Those are good enough odds that I : would bet my life on it for a one-off project.
: If one really wanted to increase the odds of being unique, I'd suggest : downloading the list of registered OUI's [ :
] and look for a company that : has gone bankrupt and disappeared. A non-existant company is not likely to : sue you if one of their (non-existant) users' equipment breaks because : you've used their addressing space.