Obtaining valid MAC addresses

[JBM]

I'm currently in development of a TCP/IP controlled device which may well go "to market". ( It's using an ENC28J60 and a PIC18F6720 if anyone's interested ). My concern is that of having a valid MAC address for each unit.

I know that for the small fee of 1650US$ I could register my company with the IEE (i thi) and then have an awful lot of MAC addresses, though I can't see my rather niche application warranting such an outlay!

So: has anyone any experience in purchasing small numbers of MAC addresses? I don't mean "eeproms with MAC addresses stored on them" (which I have seen) - I mean just the numbers!
Thanks
-JBM

[PCM programmer]

You can get a block of 4096 for $550(US):
http://standards.ieee.org/regauth/oui/pilot-ind.html

[Darren Rook]

Or just fill it with random numbers. The odds of another NIC being on the same network with the same MAC address would be extremely low.

That's probably not legal though - but who enforces such things?

[Darren Rook]

Or just fill it with random numbers. The odds of another NIC being on the same network with the same MAC address would be extremely low.

That's probably not legal though - but who enforces such things?

[asmallri]

Here are a few other options:

1. Go to the local flea market and buy old ISA adapters - they can be had for $0.50 each or less.

2. From memory (I may be wrong) the OUI 10 00 00 is public - does not belong to anyone. Therefore you can use MAC addresses in the range of 100000000000 to 100000ffffff

3. Look at the OUI list for a company that no longer exists

4. Pick an OUI from step 2 or 3 and construct the reamined of you MAC address from a hash with you IP address. Then if there is ever a problem changing you IP address will automatically give you a different MAC address.

In the days before networking converged on IP, MAC addresses had to be globally unique. These days they only have to be unique within a single broadcast domain (within a bridged domain aka layer 2 switched network). This generally means that bridging (layer 2 switching) is limited to a single subnet. Subnets of larger that 256 nodes are rare (and indicatative very very poor network design - there is no excuse). This means if you were to pick a valid MAC address the probability of there being a duplicate in the same subnet is is 1 in 1099511627776
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Regards, Andrew

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