Re: Specifying names for tap interfaces

[Scott Solmonson <scosol%scosol.org@localhost>]

Inlined-

On Sun, Jun 24, 2012 at 5:07 PM, Jean-Yves Migeon
<jeanyves.migeon%free.fr@localhost> wrote:
> On 25.06.2012 00:33, Scott Solmonson wrote:
>> This has been a pain point for me before-
>>
>> Since MACs are UUIDs-
>
> No they are not. You can use MACs to generate UUIDs (the RFC says so),
> but it does not turn it into an UUID per-see.

Perhaps I did conceptually misspeak, you can call it a UID if you
want; the concept is the same, an identifier that is entirely unlikely
to be represented in the same machine, exceedingly unlikely to be
replicated across the same broadcast domain, and if "proper" behaviors
are followed, unlikely to be replicated anywhere on the planet... thus
it's entirely suitable for the single-box-unique-identifier-problem
scenario provided.

> 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. Well, the guy running VMs
> should play that role anyway, but in the real world nobody does nor
> cares. 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.

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

> 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 based
> on 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.
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.

-SS

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