Even at 10% fill, that is 4k devices per person alive. In the short term, 281 trillion addresses, even with a low fill rate, are a lot to work with. New applications that don't need backwards compatibility are strongly advised to use EUI-64 instead.'MAC address exhaustion is unlikely to ever be a problem.

The IEEE has some concerns about the possibility of MAC address exhaustion, mainly driven by applications that assign large numbers of MAC adddresses to the same device. Smaller blocks are now available but only in a very limited range of sizes, so there is still a lot of wastage.

Most vendors will never use that many leading to lots of wasted addresses.

MAC addresses were traditionally allocated to a vendor in blocks of 2 24.

Two bits are special, one indicates whether an address is 'local' or 'global', the other indicates whether it is unicast or multicast.

So that gives 2^48 addresses, however not all of them are usable for a few reasons. It means that there are nk combinations.Ī MAC address is a 48 bit binary number, conventionally written as six hexadecimal numbers each with two digits. And it chooses from 36 chars (A-Z,0-9) - n. Most VM software and at least one hardware vendor assign addresses randomly from within a vendor ID (which may or may not actually belong to the vendor in question) and just work on the assumption that the number of devices on a network will be small enough that MAC collisions are unlikely.

In practice some vendors are sloppier about this than others.

This was acheived through splitting the address into a vendor part and then a part that could be assigned by the vendor. The way this was supposed to be ensured was by making the default MAC address of devices globally unique. Strictly speaking it only has to be unique on the local network. I know that MAC address has to be unique.

Mac address vendor codes.