host-identifier with IPv6

[Simon Hobson]

Ted Lemon wrote:

>Actually, I did cover that.   If you are tracking the Mac address, 
>and the DUID contains the Mac address, then you need one exception 
>policy.   If you are getting the Mac address directly, you need a 
>different exception policy.   But in either case, you need an 
>exception policy.



>Your life is, however, definitely easier if you track the DUID than 
>if you track the Mac address.

That is what people on the ground are disputing !

You have a blank box, it has no DUID - none currently exists for the 
device (unless it's using DUID-EE). So you have to track it by 
something that DOES exist and at the moment the ONLY identify that 
every (ethernet) device carries is one (or more) MAC address.

When a device appears with an unknown GUID you then have to extract 
the MAC, match the MAC to a (hopefully) known device, and then add 
the tracking for the GUID to the tracking system.

When a device boots a different OS - PXE, Windows, Linux, Something 
else - then it appears with a different GUID and the process has to 
be repeated.


It would appear to be even messier if an interface is moved between 
machines. Not only do you have to manually update the MAC-Device 
mapping database, you have to make sure that under no circumstances 
will your systems ever use the MAC derived from a GUID other than for 
the initial matching of an unknown GUID.

And here is a corner case for you - what about a device configured 
and generating a GUID using a MAC it no longer carries (eg the USB 
ethernet adapter previously mentioned) AND which you haven't seen on 
your network before ? The MAC address either isn't in your database, 
or even worse may be in the database assigned to another device. When 
you try and match the GUID to the device, it will match the wrong 
device and potentially get configured with the wrong setup.



So :
MAC address - static, known, globally unique*, limited number of 
values (one per NIC)
DUID - changeable (every time an OS gets re-installed), unknown, 
globally unique**, unlimited number of values per device


* OK, so some people have messed up - that affects much more than DHCP !
** You rely on 'time' to make DUID-LLT unique if NICs get moved.
-- 
Simon Hobson

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