Le 25/06/2012 01:43, Scott Solmonson a écrit :
Perhaps I did conceptually misspeak, you can call it a UID if youwant; the concept is the same, an identifier that is entirely unlikelyto be represented in the same machine, exceedingly unlikely to bereplicated across the same broadcast domain, and if "proper" behaviors are followed, unlikely to be replicated anywhere on the planet... thusit's entirely suitable for the single-box-unique-identifier-problem scenario provided.
Sure it is, but what about virtual interfaces like tap(4)? We are not talking about hardware NIC, but virtual ones.
Virtualization-platform-providers are given the same individual MAC prefixes as anyone else building network interfaces. (the NIC manufacturers you speak of) For example, VMWare's OUI is 00:50:56 - For reference: http://pubs.vmware.com/vsphere-esxi-4-1-installable/wwhelp/wwhimpl/js/html/wwhelp.htm#context=server_config&file=c_mac_addresses_generation.html
Which lets 3 bytes of randmoness for the suffix. Not a whole lot if you want to avoid collisions given the birthday paradox.
If the name assignment was not (partially) automated, you would have to rewrite your firewall/network config files each time your system boots, because the one-time mapping is not valid anymore. Annoying, even more so when you are a VPS provider with thousands of thousands of VMs basedon the same skeleton.I'm not sure which VM platforms you're working with, but this is not the behavior of anything I've touched.
Xen and KVM/Qemu. None provided a way to serialize VM configuration for a complete VM lifecycle (like VMWare's datastores), it only exists while the VM runs.
BTW that was one of the selling point of KVM: "hassle-free config files, just like Qemu."
MAC addresses for the virtual interfaces are randomly determined at "VM Create" time, according to the assigned vendor-specific prefix as described above, and (again only in the platforms I've worked with) they surely don't re-generate on every reboot.
For those given above, unless you set it by hand, it is randomly generated each time the VM is created.
-- Jean-Yves Migeon