[Dibbler] Content of duid

Simon Hobson linux at thehobsons.co.uk
Wed Jun 27 09:20:18 CEST 2012

Karl Auer wrote:

>  > real world the MAC address is no worse (and potentially better, less
>>  volatile, commonly available before a system is connected and turned
>>  on) than most DUIDs
>Less volatile in that it stays the same as long a the NIC doesn't change
>and no-one changes the MAC manually, which is entirely possible on some
>equipment. On the other hand the MAC address is more volatile in that if
>you swap the NIC out, the MAC address changes (a DUID doesn't). And with
>MAC addresses, you have to deal with multiple identities for one machine
>if the machine has multiple NICS.

My experience is that in the real world, NIC changes are fairly 
infrequent (most machines use the built-in NIC for their whole 
lifetime). On the other hand, until there is a mechanism for 
persistently storing a DUID **AND** every vendor of every OS and 
every vendor of hardware all universally support it, then the DUID is 
likely to change between OS boots (ie PXE, Windows, Linux all use 
different values) and across OS reinstalls. I can't help think that 
certain vendors won't be keen to support something like that as 
they'll have their own proprietary ideas.

At work I'd say the guys wipe and rebuild machines for customers far 
more often than they change NICs.

While it's perfectly possible to preserve a DUID across such a 
rebuild, in practice I wouldn't expect many DIYers to bother. Pros 
might if battered around enough with a clue-by-three ...

>It seems obvious to me that as IPv6 gains traction, people buying
>pre-installed operating systems will find a DUID printed on the box or
>on the underside of the machine, just as MAC addresses now commonly are.

Yes, that would work, but see above about the requirement for 
persistent machine level (not on disk) storage and support from all 
vendors. The cynic in me thinks I might make a call down below, I've 
got this idea for a skating rink !

>I'm sure none of this is new to anyone here.

It's an old argument, and so far I see it being no nearer resolution. 
But we'll see. At the moment, I see neither as perfect, but at the 
moment, the MAC address is less imperfect as an identifier.

Simon Hobson

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