can you use a random alternate mac address

It's critical to understand that if you happen to generate the same version 4 UUID as I do, in most cases, it doesn't matter. Unless you're accepting IDs on, say, an Internet-wide scale, or with an untrusted environment where malicious individuals might be able to do something bad in the case of an ID collision, it's just not something you should worry about. Realistically, none of these events occur by accident within a single application's ID space. Collisions should not occur unless one of the following happens: The MAC address is spoofed One machine running two different UUID generating applications produces UUIDs at the exact same moment Two machines without a network card or without user level access to the MAC address are given the same random node sequence, and generate UUIDs at the exact same moment We run out of bytes to represent the timestamp and rollover back to zero. If two UUIDs are generated in sequence fast enough that the timestamp matches the previous UUID, the timestamp is incremented by 1. In the case of a machine that doesn't have a MAC address, the 6 node bytes are generated with a cryptographically secure random number generator. They use the network card's MAC address (which unless spoofed, should be unique), plus a timestamp, plus the usual bit-twiddling to generate the UUID. Collisions here are only possible if the underlying hash function also has a collision. This will, for example, allow you to produce a UUID from a URL.

Version 5 and Version 3 UUIDs use the SHA1 and MD5 hash functions respectively, to combine a namespace with a piece of already unique data to generate a UUID. These are extremely unlikely to collide, but it could happen if a PRNG is used or if you just happen to have really, really, really, really, really bad luck. Version 4 UUIDs are essentially just 16 bytes of randomness pulled from a cryptographically secure random number generator, with some bit-twiddling to identify the UUID version and variant. I wrote the UUID generator/parser for Ruby, so I consider myself to be reasonably well-informed on the subject.

Can you use a random alternate mac address