Re: Specifying names for tap interfaces

[Mouse <mouse%Rodents-Montreal.ORG@localhost>]

>> Since MACs are UUIDs-
> No they are not.

Agreed.  They aren't even the same size - MACs are 48 bits while UUIDs
are 128 bits.

> When you work with VMs the MAC is very, very often randomly
> generated, because you do not have a centralized entity (the NIC's
> manufacturer) that assigns a unique MAC address to the card.  [...]
> It is the half-bogus way of ensuring you do not end up having
> multiple VMs with the same MAC address somewhere on your LAN.

That's what the `locally administered' bit in MACs is for.  In theory,
you should do your own MAC allocation and assignment, making sure to
set the lcoally-administered bit in each resulting MAC.

In practice, because there are 46 bits available to be randomized (MACs
are 48 bits, but two bits have semantic meaning and are not available
for randomization), you have to have many thousands of hosts in the
same MAC domain before the chance of collision between randomly
generated MACs becomes significant - assuming decent randomness, which
admittedly is not always a safe assumption, especially for numbers
generated early at boot.

> Annoying, even more so when you are a VPS provider with thousands of
> thousands of VMs based on the same skeleton.

Don't forget, MACs need to be unique only within each MAC domain (which
mostly means broadcast domain, unless you have very broken switches).

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