Hey Lennart, On Tue, May 03, 2022 at 09:42:40AM +0200, Lennart Poettering wrote: > For this MAC address usecase it's entirely sufficient to be able to > distinguish if the system was closed at all, i.e. if the counter is > zero or is non-zero. Because that would already be great for a policy > of "hash it in a stable way from /etc/machine-id, if counter == 0" + > "use random MAC once counter > 0". Hm, are you sure that's actually what you want? It turns out this vmgenid notification from the hypervisor might not be sufficiently granular for this use case: - vmgenid changes when you fork a new snapshot, so now you have two VMs - vmgenid also changes when you rewind to 2 minutes ago The first is what I assume you care about for this networkd business. The second is probably not what any networkd user expects. [Aside: I hope there are few networkd users; having seen what Yu did with wireguard and how fast and recklessly that went, I can't recommend that part of systemd to anyone.] >From the perspective of randomness, both of these events imply the same thing. The situation is BAD; reseed immediately. From the perspective of MAC addresses, though, these events would imply different behavior, right? So it seems like vmgenid might need an additional field for this use case. Relatedly, VMware has that prompt where you select about your VM whether, "I moved it" or "I copied it." Presumably something like that would play a part in what is decided as part of this hypothetical second field. Let me know if this seems right to you, or if actually you had in mind changing MAC addresses in both cases instead. Jason
